Patent Grant
9631195
The present disclosure generally relates to methods of producing spinosyn with reduced impurities and to spinactin and its biosynthesis.
As disclosed in U.S. Pat. No. 5,362,634, fermentation product A83543 is a family of related compounds produced by Saccharopolyspora spinosa. The known members of this family have been referred to as factors or components, and each has been given an identifying letter designation. These compounds are hereinafter referred to as spinosyn A, B, etc. The spinosyn compounds are useful for the control of arachnids, nematodes and insects, in particular, Lepidoptera and Diptera species, and they are quite environmentally friendly and have an appealing toxicological profile.
The naturally produced spinosyn compounds consist of a 5,6,5-tricylic ring system, fused to a 12-membered macrocyclic lactone, a neutral sugar (rhamnose) and an amino sugar (forosamine) (see Kirst et al. (1991). If the amino sugar is not present, the compounds have been referred to as the pseudoaglycone of A, D, etc., and if the neutral sugar is not present, then the compounds have been referred to as the reverse pseudoaglycone of A, D, etc. A more preferred nomenclature is to refer to the pseudoaglycones as spinosyn A 17-Psa, spinosyn D 17-Psa, etc., and to the reverse pseudoaglycones as spinosyn A 9-Psa, spinosyn D 9-Psa, etc.
The naturally produced spinosyn compounds may be produced via fermentation from cultures NRRL 18395, 18537, 18538, 18539, 18719, 18720, 18743 and 18823. These cultures have been deposited and made part of the stock culture collection of the Midwest Area Northern Regional Research Center, Agricultural Research Service, United States Department of Agriculture, 1815 North University Street, Peoria, Ill., 61604.
U.S. Pat. No. 5,362,634 and corresponding European Patent Application No. 375316 A1 relate to spinosyns A, B, C, D, E, F, G, H, and J. These compounds are said to be produced by culturing a strain of the novel microorganism Saccharopolyspora spinosa selected from NRRL 18395, NRRL 18537, NRRL 18538, and NRRL 18539.
WO 93/09126 relates to spinosyns L, M, N, Q, R, S, and T. Also discussed therein are two spinosyn J producing strains: NRRL 18719 and NRRL 18720, and a strain that produces spinosyns Q, R, S, and T: NRRL 18823.
WO 94/20518 and U.S. Pat. No. 5,670,486 relate to spinosyns K, O, P, U, V, W, and Y, and derivatives thereof. Also discussed is spinosyn K-producing strain NRRL 18743.
A challenge in producing spinosyn compounds arises from the fact that a very large fermentation volume is required to produce a very small quantity of spinosyns. It is highly desired to increase spinosyn production efficiency and thereby increase availability of the spinosyns while reducing their cost.
Another challenge is the production of spinosyn compounds through methods that reduce or remove impurities while having no deleterious effect on spinosyn production levels.
A particular embodiment of the invention includes a method for producing a spinosyn producing strain that comprises modifying a nucleic acid molecule encoding for spinactin by introducing, mutating, deleting, replacing or inactivating a nucleic acid sequence encoding one or more activities encoded by said nucleic acid molecule. Such introduced, mutated, deleted, replaced or inactivated sequence can result in a nucleic acid molecule encoding a spinosyn that synthesizes a polyketide other than the polyketide synthesized from a native spinosyn producing strain. Another embodiment includes a host cell that includes a nucleic acid molecule encoding a modified spinosyn, wherein said molecule is obtained by the aforementioned method.
Another embodiment includes a method for producing a modified Saccharopolyspora spinosa organism. The method includes: providing a nucleic acid comprising a nucleotide sequence within the spinactin biosynthetic gene cluster of S. spinosa; mutating the nucleotide sequence; and introducing the nucleic acid comprising the mutated nucleotide sequence into a host S. spinosa organism, such that the nucleic acid is stably integrated into the genomic DNA of the host S. spinosa organism, thereby producing a modified S. spinosa organism, wherein a gene within the spinactin biosynthetic gene cluster no longer expresses a functional protein.
Certain embodiments include a method for producing a mixture of spinosyns. The method includes: providing a culture of at least one Saccharopolyspora spinosa organism comprising a means for disrupting spinactin biosynthesis; culturing at least one S. spinosa organism under fermentation conditions; and obtaining a mixture of spinosyns from the S. spinosa fermentation culture. In further embodiment, a method for producing spinosyns includes: providing a modified Saccharopolyspora spinosa organism made according to the aforementioned method; and culturing the organism under fermentation conditions, thereby producing at least one spinosyn.
Yet another embodiment is drawn to a compound having the formula (I):
or a salt or N-oxide thereof. In a particular embodiment, a method for isolating the compound of formula (I) includes: culturing Saccharopolyspora spinosa strain, NRRL 18395, under fermentation conditions; obtaining a technical material comprising secondary metabolites from the S. spinosa fermentation culture; forming a slurry of the technical material in a solution comprising methanol and water in equal amounts (1:1); and filtering the slurry, so as to form a filtrate comprising an enriched quantity of the compound; then separating compound (I) from the spinosyn factors by preparative liquid chromatography.
The foregoing and other features will become more apparent from the following detailed description of several embodiments, which proceeds with reference to the accompanying figures.
The nucleic acid sequences listed in the accompanying sequence listing are shown using standard letter abbreviations for nucleotide bases, as defined in 37 C.F.R. §1.822. Only one strand of each nucleic acid sequence is shown, but the complementary strand is understood to be included by any reference to the displayed strand. In the accompanying sequence listing:
and
Spinosyn biosynthetic genes and related ORFs were cloned and the DNA sequence of each was determined. The cloned genes and ORFs are designated hereinafter as spnA, spnB, spnC, spnD, spnE, spnF, spnG, spnH, spnl, spnJ, spnK, spnL, spnM, spnN, spnO, spnP, spnQ, spnR, spnS, ORFL15, ORFL16, ORFR1, ORFR2, S. spinosa gtt, S. spinosa gdh, S. spinosa epi, and S. spinosa kre.
Saccharopolyspora spinosa produces a mixture of nine closely related compounds collectively called “spinosyns.” Within the mixture, spinosyn A and D, known as spinosad, are the major components and have the highest activity against key insect targets. Spinosyn J and L, two of the minor components within the spinosyn mixture, are the precursors for spinetoram, the second generation spinosyn insecticide.
Spinosad is an insecticide produced by Dow AgroSciences (Indianapolis, Ind.) that is comprised mainly of approximately 85% spinosyn A and approximately 15% spinosyn D. Spinosyn A and D are natural products produced by fermentation of Saccharopolyspora spinosa, as disclosed in U.S. Pat. No. 5,362,634. Spinosad is an active ingredient of several insecticidal formulations available commercially from Dow AgroSciences, including the TRACER™, SUCCESS™, SPINTOR™, and CONSERVE™ insect control products. For example, the TRACER product is comprised of about 44% to about 48% Spinosad (w/v), or about 4 pounds of Spinosad per gallon. Spinosyn compounds in granular and liquid formulations have established utility for the control of arachnids, nematodes, and insects, in particular Lepidoptera, Thysanoptera, and Diptera species. Spinosyn A and D is also referred to herein as Spinosyn A/D.
Spinetoram is a mixture of 5,6-dihydro-3′-ethoxy spinosyn J (major component) and 3′-ethoxy spinosyn L produced by Dow AgroSciences. The mixture can be prepared by ethoxylating a mixture of spinosyn J and spinosyn L, followed by hydrogenation. The 5,6 double bond of spinosyn J and its 3′-ethoxy is hydrogenated much more readily than that of spinosyn L and its 3′-ethoxy derivative, due to steric hindrance by the methyl group at C-5 in spinosyn L and its 3′-ethoxy derivative. See, U.S. Pat. No. 6,001,981. Spinosyn J and L is also referred to herein as Spinosyn J/L.
Novel spinosyns can also be produced by mutagenesis of the cloned genes, and substitution of the mutated genes for their unmutated counterparts in a spinosyn-producing organism. Mutagenesis may involve, for example: 1) deletion or inactivation of a ketoreductase, dehydratase or enoyl reductase (KR, DH, or ER) domain so that one or more of these functions is blocked and the strain produces a spinosyn having a lactone nucleus with a double bond, a hydroxyl group, or a keto group that is not present in the nucleus of spinosyn A (see Donadio et al., 1993); 2) replacement of an AT domain so that a different carboxylic acid is incorporated in the lactone nucleus (see Ruan et al., 1997); 3) addition of a KR, DH, or ER domain to an existing PKS module so that the strain produces a spinosyn having a lactone nucleus with a saturated bond, hydroxyl group, or double bond that is not present in the nucleus of spinosyn A; or 4) addition or subtraction of a complete PKS module so that the cyclic lactone nucleus has a greater or lesser number of carbon atoms. A hybrid PKS can be created by replacing the spinosyn PKS loading domain with heterologous PKS loading. See, e.g., U.S. Pat. No. 7,626,010. It has further been noted that spinosyns via modification of the sugars that are attached to the spinosyn lactone backbone can include modifications of the rhamnose and/or forosamine moiety or attachment of different deoxy sugars. The Salas group in Spain demonstrated that novel polyketide compounds can be produced by substituting the existing sugar molecule with different sugar molecules. Rodriguez et al. J. Mol. Microbiol Biotechnol. 2000 July; 2(3):271-6. The examples that follow throughout the application help to illustrate the use of mutagenesis to produce a spinosyn with modified functionality.
The DNA from the spinosyn gene cluster region can be used as a hybridization probe to identify homologous sequences. Thus, the DNA cloned here could be used to locate additional plasmids from the Saccharopolyspora spinosa gene libraries which overlap the region described here but also contain previously uncloned DNA from adjacent regions in the genome of Saccharopolyspora spinosa. In addition, DNA from the region cloned here may be used to identify non-identical but similar sequences in other organisms. Hybridization probes are normally at least about 20 bases long and are labeled to permit detection.
According to a particular embodiment of the invention, a method for producing a spinosyn producing strain comprises modifying a nucleic acid molecule encoding for spinactin by introducing, mutating, deleting, replacing or inactivating a nucleic acid sequence encoding one or more activities encoded by said nucleic acid molecule. Such introduced, mutated, deleted, replaced or inactivated sequence can result in a nucleic acid molecule encoding a spinosyn that synthesizes a polyketide other than the polyketide synthesized from a native spinosyn producing strain. The spinosyn producing strain may produce spinosyns A and D, and in particular embodiments, may produce spinosyns J and L.
The terms “stringent conditions” or “hybridization under stringent conditions” refers to conditions under which a probe will hybridize preferentially to its target subsequence, and to a lesser extent to, or not at all to, other sequences. “Stringent hybridization” and “stringent hybridization wash conditions” in the context of nucleic acid hybridization experiments such as Southern and Northern hybridizations are sequence dependent, and are different under different environmental parameters. An extensive guide to the hybridization of nucleic acids is found in Tijssen (1993) Laboratory Techniques in Biochemistry and Molecular Biology—Hybridization with Nucleic Acid Probes part I chapter 2 Overview of principles of hybridization and the strategy of nucleic acid probe assays, Elsevier, N.Y. Generally, highly stringent hybridization and wash conditions are selected to be about 5° C. lower than the thermal melting point (Tm) for the specific sequence at a defined ionic strength and pH. The Tm, is the temperature (under defined ionic strength and pH) at which 50% of the target sequence hybridizes to a perfectly matched probe. Very stringent conditions are selected to be equal to the Tm for a particular probe.
An example of stringent hybridization conditions for hybridization of complementary nucleic acids which have more than 100 complementary residues on a filter in a Southern or Northern blot is 50% formamide with 1 mg of heparin at 42° C., with the hybridization being carried out overnight. An example of highly stringent wash conditions is 0.15 M NaCl at 72° C. for about 15 minutes. An example of stringent wash conditions is a 0.2×SSC (sodium chloride/sodium citrate buffer) wash at 65° C. for 15 minutes (see, Sambrook et al. (1989) Molecular Cloning—A Laboratory Manual (2nd ed.) Vol. 1-3, Cold Spring Harbor Laboratory, Cold Spring Harbor Press, NY, for a description of SSC buffer). Often, a high stringency wash is preceded by a low stringency wash to remove background probe signal. An example medium stringency wash for a duplex of, e.g., more than 100 nucleotides, is 1×SSC at 45° C. for 15 minutes. An example low stringency wash for a duplex of, e.g., more than 100 nucleotides, is 4-6×SSC at 40° C. for 15 minutes. In general, a signal to noise ratio of 2× (or higher) than that observed for an unrelated probe in the particular hybridization assay indicates detection of a specific hybridization. Nucleic acids which do not hybridize to each other under stringent conditions are still substantially identical if the polypeptides which they encode are substantially identical. This occurs, e.g., when a copy of a nucleic acid is created using the maximum codon degeneracy permitted by the genetic code.
The invention also relates to an isolated polynucleotide hybridizable under stringent conditions, preferably under highly stringent conditions, to a polynucleotide as of the present invention.
As used herein, the term “hybridizing” is intended to describe conditions for hybridization and washing under which nucleotide sequences at least about 50%, at least about 60%, at least about 70%, more preferably at least about 80%, even more preferably at least about 85% to 90%, most preferably at least 95% homologous to each other typically remain hybridized to each other.
In one embodiment, a nucleic acid of the invention is at least 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or more homologous to a nucleic acid sequence shown in this application or the complement thereof.
Another non-limiting example of stringent hybridization conditions is hybridization in 6×SSC at about 45° C., followed by one or more washes in 1×SSC, 0.1% SDS at 50° C., preferably at 55° C. more preferably at 60° C. and even more preferably at 65° C.
Highly stringent conditions can include incubations at 42° C. for a period of several days, such as 2-4 days, using a labeled DNA probe, such as a digoxigenin (DIG)-labeled DNA probe, followed by one or more washes in 2×SSC, 0.1% SDS at room temperature and one or more washes in 0.5×SSC, 0.1% SDS or 0.1×SSC, 0.1% SDS at 65-68° C. In particular, highly stringent conditions include, for example, 2 h to 4 days incubation at 42° C. using a DIG-labeled DNA probe (prepared by e.g. using a DIG labeling system; Roche Diagnostics GmbH, 68298 Mannheim, Germany) in a solution such as DigEasyHyb solution (Roche Diagnostics GmbH) with or without 100 μg/ml salmon sperm DNA, or a solution comprising 50% formamide, 5×SSC (150 mM NaCl, 15 mM trisodium citrate), 0.02% sodium dodecyl sulfate, 0.1% N-lauroylsarcosine, and 2% blocking reagent (Roche Diagnostics GmbH), followed by washing the filters twice for 5 to 15 minutes in 2×SSC and 0.1% SDS at room temperature and then washing twice for 15-30 minutes in 0.5×SSC and 0.1% SDS or 0.1×SSC and 0.1% SDS at 65-68° C.
In some embodiments an isolated nucleic acid molecule of the invention that hybridizes under highly stringent conditions to a nucleotide sequence of the invention can correspond to a naturally occurring nucleic acid molecule. As used herein, a “naturally occurring” nucleic acid molecule refers to an RNA or DNA molecule having a nucleotide sequence that occurs in nature (e.g., encodes a natural protein).
A skilled artisan will know which conditions to apply for stringent and highly stringent hybridization conditions. Additional guidance regarding such conditions is readily available in the art, for example, in Sambrook et al., 1989, Molecular Cloning, A Laboratory Manual, Cold Spring Harbor Press, N.Y.; and Ausubel et al. (eds.), 1995, Current Protocols in Molecular Biology, (John Wiley & Sons, N.Y.).
“Functional polymorphism” as used herein refers to a change in the base pair sequence of a gene that produces a qualitative or quantitative change in the activity of the protein encoded by that gene (e.g., a change in specificity of activity; a change in level of activity). The term “functional polymorphism” includes mutations, deletions and insertions.
In general, the step of detecting the polymorphism of interest may be carried out by collecting a biological sample containing DNA from the source, and then determining the presence or absence of DNA containing the polymorphism of interest in the biological sample.
Determining the presence or absence of DNA encoding a particular mutation may be carried out with an oligonucleotide probe labeled with a suitable detectable group, and/or by means of an amplification reaction such as a polymerase chain reaction or ligase chain reaction (the product of which amplification reaction may then be detected with a labeled oligonucleotide probe or a number of other techniques). Further, the detecting step may include the step of detecting whether the subject is heterozygous or homozygous for the particular mutation. Numerous different oligonucleotide probe assay formats are known which may be employed to carry out the present invention. See, e.g., U.S. Pat. No. 4,302,204 to Wahl et al.; U.S. Pat. No. 4,358,535 to Falkow et al.; U.S. Pat. No. 4,563,419 to Ranki et al.; and U.S. Pat. No. 4,994,373 to Stavrianopoulos et al.
Amplification of a selected, or target, nucleic acid sequence may be carried out by any suitable means. See generally, Kwoh et al., Am. Biotechnol. Lab. 8, 14-25 (1990). Examples of suitable amplification techniques include, but are not limited to, polymerase chain reaction, ligase chain reaction, strand displacement amplification (see generally G. Walker et al., Proc. Natl. Acad. Sci. USA 89, 392-396 (1992); G. Walker et al., Nucleic Acids Res. 20, 1691-1696 (1992)), transcription-based amplification (see D. Kwoh et al., Proc. Natl. Acad. Sci. USA 86, 1173-1177 (1989)), self-sustained sequence replication (or “3SR”) (see J. Guatelli et al., Proc. Natl. Acad. Sci. USA 87, 1874-1878 (1990)), the QI3 replicase system (see P. Lizardi et al., BioTechnology 6, 1197-1202 (1988)), nucleic acid sequence-based amplification (or “NASBA”) (see R. Lewis, Genetic Engineering News 12 (9), 1 (1992)), the repair chain reaction (or “RCR”) (see R. Lewis, supra), and boomerang DNA amplification (or “BDA”) (see R. Lewis, supra). Polymerase chain reaction is generally preferred.
Polymerase chain reaction (PCR) may be carried out in accordance with known techniques. See, e.g., U.S. Pat. Nos. 4,683,195; 4,683,202; 4,800,159; and 4,965,188. In general, PCR involves, first, treating a nucleic acid sample (e.g., in the presence of a heat stable DNA polymerase) with one oligonucleotide primer for each strand of the specific sequence to be detected under hybridizing conditions so that an extension product of each primer is synthesized which is complementary to each nucleic acid strand, with the primers sufficiently complementary to each strand of the specific sequence to hybridize therewith so that the extension product synthesized from each primer, when it is separated from its complement, can serve as a template for synthesis of the extension product of the other primer, and then treating the sample under denaturing conditions to separate the primer extension products from their templates if the sequence or sequences to be detected are present. These steps are cyclically repeated until the desired degree of amplification is obtained. Detection of the amplified sequence may be carried out by adding to the reaction product an oligonucleotide probe capable of hybridizing to the reaction product (e.g., an oligonucleotide probe of the present invention), the probe carrying a detectable label, and then detecting the label in accordance with known techniques, or by direct visualization on a gel. Such probes may be from 5 to 500 nucleotides in length, preferably 5 to 250, more preferably 5 to 100 or 5 to 50 nucleic acids. When PCR conditions allow for amplification of all allelic types, the types can be distinguished by hybridization with an allelic specific probe, by restriction endonuclease digestion, by electrophoresis on denaturing gradient gels, or other techniques.
Ligase chain reaction (LCR) is also carried out in accordance with known techniques. See, e.g., R. Weiss, Science 254, 1292 (1991). In general, the reaction is carried out with two pairs of oligonucleotide probes: one pair binds to one strand of the sequence to be detected; the other pair binds to the other strand of the sequence to be detected. Each pair together completely overlaps the strand to which it corresponds. The reaction is carried out by, first, denaturing (e.g., separating) the strands of the sequence to be detected, then reacting the strands with the two pairs of oligonucleotide probes in the presence of a heat stable ligase so that each pair of oligonucleotide probes is ligated together, then separating the reaction product, and then cyclically repeating the process until the sequence has been amplified to the desired degree. Detection may then be carried out in like manner as described above with respect to PCR.
The terms “homology” or “percent identity” are used interchangeably herein. For the purpose of this invention, it is defined here that in order to determine the percent identity of two amino acid sequences or of two nucleic acid sequences, the sequences are aligned for optimal comparison purposes (e.g., gaps may be introduced in the sequence of a first amino acid or nucleic acid sequence for optimal alignment with a second amino or nucleic acid sequence). The amino acid residues or nucleotides at corresponding amino acid positions or nucleotide positions are then compared. When a position in the first sequence is occupied by the same amino acid residue or nucleotide as the corresponding position in the second sequence, then the molecules are identical at that position. The percent identity between the two sequences is a function of the number of identical positions shared by the sequences (i.e., % identity=number of identical positions/total number of positions (i.e., overlapping positions×100). Preferably, the two sequences are the same length.
The skilled person will be aware of the fact that several different computer programs are available to determine the homology between two sequences. For instance, a comparison of sequences and determination of percent identity between two sequences may be accomplished using a mathematical algorithm. In a preferred embodiment, the percent identity between two amino acid sequences is determined using the Needleman and Wunsch (J. Mol. Biol. (48): 444-453 (1970)) algorithm which has been incorporated into the GAP program in the GCG software package (available on the interne at the accelrys website, more specifically at _accelrys(dot)com), using either a Blossom 62 matrix or a PAM250 matrix, and a gap weight of 16, 14, 12, 10, 8, 6 or 4 and a length weight of 1, 2, 3, 4, 5 or 6. The skilled person will appreciate that all these different parameters will yield slightly different results but that the overall percentage identity of two sequences is not significantly altered when using different algorithms.
In yet another embodiment, the percent identity between two nucleotide sequences is determined using the GAP program in the GCG software package (available on the internet at the accelrys website, more specifically at _accelrys(dot)com), using a NWSgapdna.CMP matrix and a gap weight of 40, 50, 60, 70 or 80 and a length weight of 1, 2, 3, 4, 5 or 6. In another embodiment, the percent identity between two amino acid or nucleotide sequences is determined using the algorithm of E. Meyers and W. Miller (CABIOS, 4: 11-17 (1989) which has been incorporated into the ALIGN program (version 2.0) (available on the internet at the vega website, more specifically ALIGN-IGH Montpellier, or more specifically at _vega(dot)igh(dot)cnrs(dot)fr/bin/align-guess(dot)cgi) using a PAM120 weight residue table, a gap length penalty of 12 and a gap penalty of 4.
The nucleic acid and protein sequences of the present invention may further be used as a “query sequence” to perform a search against public databases to, for example, identify other family members or related sequences. Such searches may be performed using the BLASTN and BLASTX programs (version 2.0) of Altschul, et al. (1990) J. Mol. Biol. 215:403-10. BLAST nucleotide searches may be performed with the BLASTN program, score=100, word length=12 to obtain nucleotide sequences homologous to the nucleic acid molecules of the present invention. BLAST protein searches may be performed with the BLASTX program, score=50, word length=3 to obtain amino acid sequences homologous to the protein molecules of the present invention. To obtain gapped alignments for comparison purposes, Gapped BLAST may be utilized as described in Altschul et al., (1997) Nucleic Acids Res. 25 (17): 3389-3402. When utilizing BLAST and Gapped BLAST programs, the default parameters of the respective programs (e.g., BLASTX and BLASTN) may be used. (Available on the internet at the ncbi website, more specifically at _ncbi(dot)nlm(dot)nih(dot)gov).
Another embodiment may include a host cell that comprises a nucleic acid molecule encoding a modified spinosyn, wherein said molecule is obtained by the aforementioned method. An alternative method may also produce a modified polyketide causing expression of a nucleic acid molecule in a host cell, which polyketide may also be further purified. In a particular embodiment, mutating, deleting, replacing or inactivating a sequence may comprise: providing a library of nucleic acids, which nucleic acids comprise one or more polynucleotide segments operably linked to at least one transcription regulatory sequence; introducing the library of nucleic acids into a population of recipient cells or intracellular organelles, whereby said nucleic acids disable spinactin production while maintaining spinosyn production; and identifying at least one recipient cell, intracellular organelle or organism comprising a recipient cell, with a desired phenotype, thereby controlling the spinosyn producing strain. Mutating the nucleotide sequence may include introducing a deletion, a mutation, or a stop codon. The nucleotide sequence may comprised within a gene that can be selected from the group consisting of: ABC transporter substrate-binding protein; amino acid ABC transporter permease; EmrB QacA family drug resistance transporter; monooxygenase; NRPS1; NRPS2; a gene located between NRPS1 and NRPS2 in the S. spinosa genome; thiazolinyl imide reductase; thioesterase; methyltransferase; pabAB; a transcriptional regulator; Acyl-CoA synthase; N-methyltransferase; pyridoxamine 5′-phosphate oxidase; 2,3-dihydrobenzoate-AMP ligase; and aminotransferase. The nucleotide sequence within the thiazolinyl imide reductase gene may be at least 80% identical to SEQ ID NO:3.
The modified S. spinosa organism can produce less spinactin than was produced in the host S. spinosa organism before introduction of the nucleic acid, or may produce no spinactin. In some embodiments, the modified S. spinosa organism can produce: an amount of spinosyn A that is substantially identical to the amount of spinosyn A produced in the host S. spinosa organism before introduction of the nucleic acid; an amount of spinosyn D that is substantially identical to the amount of spinosyn D produced in the host S. spinosa organism before introduction of the nucleic acid, and an amount of spinactin that is less than the amount of spinactin produced in the host S. spinosa organism before introduction of the nucleic acid.
A method for producing a mixture of spinosyns, the method comprising: providing a culture of at least one Saccharopolyspora spinosa organism comprising a means for disrupting spinactin biosynthesis; culturing at least one S. spinosa organism under fermentation conditions; and obtaining a mixture of spinosyns from the S. spinosa fermentation culture. Disrupting spinactin biosynthesis may be accomplished by inactivating a gene of the spinactin gene cluster or by mutating a gene in the spinactin gene cluster. The mixture of spinosyns obtained from the S. spinosa fermentation culture may include at least one of spinosyn A and spinosyn D. The mixture of spinosyns obtained from the S. spinosa fermentation culture may include no spinactin. In some embodiments, the gene of the spinactin gene cluster is a thiazolinyl imide reductase gene. A modified Saccharopolyspora spinosa organism may be produced by the method. The organism may include a transgene involved in spinosyn biosynthesis. The modified S. spinosa organism may include a transgene involved in spinosyn biosynthesis that is stably integrated into the genomic DNA of the organism at a site wherein the nucleic acid was stably integrated.
Another embodiment of the invention includes a modified Saccharopolyspora spinosa organism comprising a means for disrupting spinactin synthesis, wherein the organism is capable of producing spinosyn A and/or spinosyn D without producing a significant amount of spinactin.
Another embodiment includes a method for producing a modified Saccharopolyspora spinosa organism. The method includes: providing a nucleic acid comprising a nucleotide sequence within the spinactin biosynthetic gene cluster of S. spinosa; mutating the nucleotide sequence; and introducing the nucleic acid comprising the mutated nucleotide sequence into a host S. spinosa organism, such that the nucleic acid is stably integrated into the genomic DNA of the host S. spinosa organism, thereby producing a modified S. spinosa organism, wherein a gene within the spinactin biosynthetic gene cluster no longer expresses a functional protein.
In further embodiment, a method for producing spinosyns includes: providing a modified Saccharopolyspora spinosa organism made according to the aforementioned method; and culturing the organism under fermentation conditions, thereby producing at least one spinosyn.
Yet another embodiment is drawn to a compound having the formula (I):
or a salt or N-oxide thereof. In a particular embodiment, a method for isolating the compound of formula (I) includes: culturing Saccharopolyspora spinosa strain, NRRL 18395, under fermentation conditions; obtaining a technical material comprising secondary metabolites from the S. spinosa fermentation culture; forming a slurry of the technical material in a solution comprising methanol and water in equal amounts (1:1); and filtering the slurry, so as to form a filtrate comprising an enriched quantity of the compound.
The following examples are provided to illustrate certain particular features and/or embodiments. The examples should not be construed to limit the disclosure to the particular features or embodiments exemplified.
Spinactin is a sulfur-containing compound which was identified from an S. spinosa fermentation culture.
A fermentation culture of S. spinosa from strain NRRL 18395 was propagated using the fermentation protocol described in Strobel and Nakatsukasa (1993) J. Ind. Microbiol. Biotechnol. 11(2):121-7. Liquid chromatographic analysis identified the presence of a previously undetected secondary metabolite having a characteristic UV spectrum, with λmax=227 and 358 nm. The secondary metabolite was isolated using the following procedure. The technical material (3 kg) from a S. spinosa fermentation culture was slurried in methanol/water (1:1) and filtered. The filtrate was found to contain an enriched quantity of the previously undetected secondary metabolite. This secondary metabolite was separated from the remaining spinosyn material via preparative reverse phase liquid chromatography. Using this method, 6 gm of the new molecule was obtained, which accounted for about 0.02% by mass of the total technical material. The new molecule, which was named spinactin, was re-crystallized from methanol/water as a pale green solid (mp 79° C.). High resolution probe electron impact mass spectrometry (EI/MS) indicated that spinactin possessed a molecular formula of C20H28N4O3S2. Analysis of 1H, 13C and Distortionless Enhancement by Polarization Transfer (DEPT) spectra indicated the presence of a dimethylamine group, a second methylamine, and a single S-methyl group. Also apparent was a 1,2,4-trisubstituted benzene ring. The remainder of the spectrum in chloroform included complex non-first order multiplets including virtual coupling effects seen in 2-D spectra, caused by the coincident chemical shifts for 4-H and 5-H. Thus the structure was solved in methanol-d4 in which the spectrum was first-order as described below using standard 2-D NMR techniques including COSY, HSQC, and HMBC (see Table 1).
Three spin systems were readily identified in the 1H spectrum; three aromatic multiplets were detected between 7.3 and 6.7 ppm, indicating a 1,2,4-trisubstituted benzene ring containing oxygen or nitrogen substituents; another spin-system of two methylenes (one oxygen substituted, and one with nitrogen) sandwiching a methine, which also indicated nitrogen substitution; and an elongated spin-system containing three contiguous methines, with methylenes at the termini. None of the multiplets resonated at higher field than 2.5 ppm indicating a high degree of heteroatom substitution. Aside from these spin systems, there were three methyl singlets, which were shown to be a dimethyl amino group, and another N-methyl group, and a methyl thioether. The coupling constant between two of the methines was small, suggesting that the carbon atoms were not directly connected. Both of these carbon atoms had HMBC cross-peaks from the N-methyl group, indicating that they were on either side of a methylated tertiary nitrogen.
The molecule was assembled by extensive analysis of the HMBC experiments. Thus an oxazoline ring was identified with attachment to the aromatic ring at C-2. This ring was determined to have a methylene group attached to C-5, which was used as a handle to aid in the assembly of the diazabicyclooctane ring system. This methylene (resonating at 3.9 and 3.5 ppm) indicated cross-peaks to one of the methines in the extended spin system (63 ppm), and also to an amide carbonyl at 172 ppm. Further cross peaks to this carbonyl came from another methine (4.1 ppm) and one of the other methylene groups (resonating at 3.5 and 3.2 ppm) indicating a 6-membered ring containing 2 nitrogen atoms. That this methylene was bridged back into the ring, was determined by the existence of cross-peaks to both of the methines connected to the methylated nitrogen atom, the thioether deduced by chemical shift. Assembly of the rest of the molecule was readily accomplished once this ring system was determined.
1H
13C
An X-ray crystallography method was used to validate the structure of the spinactin molecule. An ORTEP (Oak Ridge Thermal Ellipsoid Program) model of the structure is shown in
Based on the structural resemblance of the 2-hydroxyphenyloxazoline moiety of spinactin as compared to the 2-hydroxyphenyloxazoline moiety of mycobactin A, it was hypothesized that both molecules are produced by similar biosynthetic pathways. The involvement of the mycobactin A biosynthetic gene cluster and the phenyloxazoline synthase mbtB gene (mbtB) in the biosynthesis of the 2-hydroxyphenyloxazoline moiety of mycobactin A was characterized in Quadri et al. (1998) 5:631-645. The amino acid sequence of phenyloxazoline synthase mbtB (Accession No: ZP_06505539) from the mycobactin gene cluster of Mycobacterium tuberculosis strain 02_1987 was used to screen, in silico, the genomic sequence obtained from the S. spinosa wild type strain (NRRL 18395). The resulting BLAST search identified the presence of a putative gene sequence from the S. spinosa genome which encoded an amino acid sequence with similarity to MbtB. The NRPS1 gene from the S. spinosa genome shared approximately 46% identity at the amino acid level with the mbtB gene from the M. tuberculosis gene cluster. The identification of this gene led to the subsequent identification of a S. spinosa gene cluster which contains additional genes that are proposed to be involved in the biosynthesis of spinactin. These gene sequences from the S. spinosa spinactin gene cluster were annotated using the computer program, FgenesB (Cambridge University, UK).
A genomic cosmid library from S. spinosa (U.S. patent application Ser. No. 13/100,202) was screened to identify cosmid clones which contained the thiazolinyl imide reductase gene. The thiazolinyl imide reductase gene is located downstream of the NRPS1 gene, and was characterized as a putative member of the spinactin gene cluster which encodes an enzyme that is non-essential for the biosynthesis of spinosyn A/D. This gene was used to identify cosmid clones that could be modified by deleting a 7.6 Kb fragment which contains the spinactin gene cluster. The resulting cosmid clones were then used to generate S. spinosa knock-out strains.
A 412 bp fragment of the thiazolinyl imide reductase gene was prepared with a PCR digoxigenin (DIG) labeling kit. The 412 bp (SEQ ID NO:3) fragment was PCR amplified using a forward primer (SEQ ID NO:4) and a reverse primer (SEQ ID NO:5). Hybridization was completed at 42° C. in commercially supplied hybridization buffer (Roche) overnight. The nylon membranes were washed under stringent conditions for 5 minutes, twice in 2×SSC, 0.1% SDS at room temperature and for 15 minutes, twice in 0.1×SSC, 0.1% SDS at 68° C. Chemiluminescent labeling and detection was carried out by using the DIG Luminescent Detection Kit™ (Roche). Three positive cosmid clones were identified (2C14, 3E11 and 4G15) and confirmed by end-sequencing of the cosmid insert using T3 and T7 sequencing primers.
The construction of an apramycin-attB cassette was completed by cloning the attB sequence into an apramycin resistance gene cassette. Synthesis of the Streptomyces lividans, actinophage φC31 attachment site sequence (attB; Accession No: X60952) was carried out by a third party service provider (Integrated DNA Technologies, Coralville, Iowa). To facilitate the cloning of the synthesized attB fragment, BamHI and NdeI sites were added to the 5′ and 3′ ends, respectively (SEQ ID NO:6). The vector which contained the synthesized attB sequence was labeled as pIDTSMART.
Template plasmid, pIJ773 (Accession No: AX657063), containing the apramycin resistance gene cassette, aac(3)-IV (Accession No: X99313), and the oriT of plasmid RP4 (Accession No: L27758), flanked by FRT sites was PCR-amplified using a forward primer2 (SEQ ID NO:7) and a reverse primer2 (SEQ ID NO:8). The PCR fragment was cloned into the pCR8/GW/TOPO™ vector (Invitrogen, Carlsbad, Calif.) as instructed by the manufacturer's protocol, and the presence and integrity of the inserted apramycin cassette was confirmed via restriction digestion and sequencing.
The attB fragment from pIDTSMART was digested with BamHI and NdeI and the resulting 300 bp DNA fragment was gel-purified using the QIAquick Gel Extraction Kit™ (Qiagen, Valencia, Calif.). The purified attB fragment was cloned into the pCR8/GW/TOPO™ vector, which contained the apramycin resistance gene cassette at the NdeI and BamHJ restriction sites, using standard molecular biological techniques. The construction of a new apramycin resistance gene cassette containing an attB attachment site was confirmed by restriction enzyme digestion and sequencing. The constructed pCR8/GW/TOPO_aac(3)-attB plasmid map and sequence are provided as
A 7.6 Kb deletion of the spinactin gene cluster was achieved by targeting the thiazolinyl imide reductase region with a apramycin-attB cassette using the Redirect Recombineering Technology™ (Gust et al. (2003) Proc. Natl. Acad. Sci. USA 100(4):1541-6). A set of primers were designed to amplify the apramycin-attB cassette using forward primer3 (SEQ ID NO:10) and reverse primer3 (SEQ ID NO:11). These primers were designed to contain 5′ sequences which shared homology to the spinactin gene cluster. The resulting PCR product was integrated into cosmid clone 4G15 by following the Redirect Recombineering protocol. A knock-out of the spinactin gene cluster within cosmid clone 4G15 resulted via a double cross over, wherein the apramycin-attB cassette replaced the native DNA sequence of cosmid clone 4G15. The resulting deletion was confirmed via DNA sequencing of the junction region. The nucleotide sequence of the junction, wherein the 7.6 Kb fragment of the spinactin gene cluster was deleted, is provided as SEQ ID NO:12.
The modified 4G15 cosmid DNA was isolated and transformed into a donor strain of E. coli, S17-1, and used in a conjugation experiment with S. spinosa strain NRRL 18538. The conjugation was completed following a protocol which had been modified to include ISP4-medium (Matsushima et al. (1994) Gene 146(1):39-45). Transconjugants were selected by flooding the conjugation media-plates with apramycin (50 μg/ml) and nalidixic acid (25 μg/ml). The transconjugants from the conjugation plates were patched onto ISP2 agar medium supplemented with 20 mM CaCl2 and apramycin (50 μg/ml) and nalidixic acid (25 μg/ml). The double cross-over knock-outs (resistant to apramycin and sensitive to kanamycin antibiotics) were selected on ISP2 agar medium containing apramycin at 50 μg/ml.
Five independent knock-out strains (labeled as 538-M2, 538-M4, 538-M6, 538-M7 and 538-M10) were selected. These knock-out strains were molecularly confirmed for the 7.6 Kb deletion of the spinactin gene cluster by PCR amplification. The PCR reactions produced a fragment of the expected size which indicated that a 7.6 Kb fragment was deleted from the genome of S. spinosa strain NRRL 18538 (See
The knock-out strains derived from S. spinosa strain NRRL 18538, which were generated to contain a partial deletion of the spinactin gene cluster, were propagated as 6-day and 10-day shake flask fermentation cultures. The knock-out strains produced levels of spinosyn A and D comparable to the control strains that contained an intact spinactin gene cluster. Moreover, undetectable or very low levels of spinactin were detected in the S. spinosa NRRL 18538 knock-out strains. These results indicate that the removal of the secondary metabolite, spinactin, does not deleteriously affect the production and biosynthesis of spinosyns A and D.
Methanol extracts of the fermentation broth from wild-type S. spinosa strain NRRL 18538 and S. spinosa strain NRRL 18538 knock-out strains were analyzed for spinactin production using a LC-UV-MS method. The methanol extraction protocol was completed wherein one part of fermentation broth and three parts of methanol were incubated overnight at room temperature. Samples of the methanol extracts were chromatographed using an Agilent Eclipse Plus C18 (100×3 mm; 1.8 μm) column at 40° C. eluted at 0.5 mL/min using a linear gradient of A:B 50:50 (0 min) to 5:95 (12 mM) where A=25 mM ammonium acetate and B=acetonitrile-methanol (80:20). Spinactin, which eluted at approximately 8.8 mM, was detected either by UV absorbance at 227 nm or by selected ion monitoring mass spectrometry (SIM-MS), monitoring the ion at m/z 437.2. Quantitation was performed using an external standard method with calibration curves established from a pure sample of spinactin. In the wild-type S. spinosa strain NRRL 18538 and S. spinosa strain NRRL 18538 knock-out strains, the UV method was used for quantitation of spinactin when present above approximately 2 mg/L, whereas the SIM-MS method was used when the compound was present in the range approximately 0.02-2 mg/L.
The resulting spinosyn A and D and spinactin titers for the fermentation broth from wild-type S. spinosa strain NRRL 18538 and S. spinosa strain NRRL 18538 knock-out strains are summarized in Table 2. These data demonstrate that a partial gene deletion within the spinactin gene cluster had no effect on the titer of spinosyn production in the S. spinosa strain NRRL 18538 knock-out strains as compared to the wild-type S. spinosa strain NRRL 18538.
An approximately 7.6 kb fragment of the spinactin biosynthetic gene cluster coding sequence including the thiazolinyl imide reductase gene was deleted, thereby abolishing spinactin production in S. spinosa strain NRRL 18538. Subsequent fermentation of the knock-out strains resulted in biosynthesis of spinosyns A and D at levels that were comparable to S. spinosa control strains. Therefore, the deletion of the 7.6 kb fragment from the spinactin biosynthetic gene cluster in S. spinosa strain NRRL 18538 resulted in the removal of the secondary metabolite, spinactin, from the felinentation culture without deleteriously effecting the production and biosynthesis of spinosyns A and D.
This application claims the benefit of U.S. Provisional Patent Application Ser. No. 61/580,947, filed Dec. 28, 2011, the disclosure of which is hereby incorporated herein in its entirety by this reference.
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| Number | Date | Country | |
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| 61580947 | Dec 2011 | US |
