Bacillus Thuringiensis Genes Encoding Nematode-Active Toxins

The soil microbe Bacillus thuringiensis (B.t.) is a Gram-positive, spore-forming bacterium characterized by parasporal crystalline protein inclusions. These inclusions often appear microscopically as distinctively shaped crystals. The proteins can be highly toxic to pests and specific in their toxic activity. Certain B.t. toxin genes have been isolated and sequenced, and recombinant DNA-based B.t. products have been produced and approved for use. In addition, with the use of genetic engineering techniques, new approaches for delivering B.t. endotoxins to agricultural environments are under development, including the use of plants genetically engineered with endotoxin genes for insect resistance and the use of stabilized intact microbial cells as B.t. endotoxin delivery vehicles (Gaertner and Kim, 1988). Thus, isolated B.t. endotoxin genes are becoming commercially valuable.

Until the last ten years, commercial use of B.t. pesticides has been largely restricted to a narrow range of lepidopteran (caterpillar) pests. Preparations of the spores and crystals of B. thuringiensis var. kurstaki have been used for many years as commercial insecticides for lepidopteran pests. For example, B. thuringiensis var. kurstaki HD-1 produces a crystal called a .delta.-endotoxin which is toxic to the larvae of a number of lepidopteran insects.

In recent years, however, investigators have discovered B.t. pesticides with specificities for a much broader range of pests. For example, other species of B.t., namely B.t. var. israelensis and B.t. var. tenebrionis (a.k.a. M-7, a.k.a. B.t. var. san diego), have been used commercially to control insects of the orders Diptera and Coleoptera, respectively (Gaertner, 1989). See also Couch, 1980 and Beegle, 1978. Krieg et al., 1983, describe Bacillus thuringiensis var. tenebrionis, which is reportedly active against two beetles in the order Coleoptera. These are the Colorado potato beetle, Leptinotarsa decemlineata, and the beetle Agelastica alni.

Recently, new subspecies of B.t. have been identified, and genes responsible for active .delta.-endotoxin proteins have been isolated (Hofte and Whiteley, 1989). Hofte and Whiteley classified B.t. crystal protein genes into 4 major classes. The classes were CryI (Lepidoptera-specific), CryII (Lepidoptera- and Diptera-specific), CryIII (Coleoptera-specific), and CryIV (Diptera-specific). Prefontaine et al., 1987, describe probes useful in classifying lepidopteran-active genes. The discovery of strains specifically toxic to other pests has been reported (Feitelson et al., 1992).

The cloning and expression of a B.t. crystal protein gene in Escherichia coli has been described in the published literature (Schnepf and Whiteley, 1981). U.S. Pat. No. 4,448,885 and U.S. Pat. No. 4,467,036 both disclose the expression of B.t. crystal proteins in E. coli. U.S. Pat. Nos. 4,797,276 and 4,853,331 disclose B. thuringiensis var. tenebrionis (a.k.a. B.t. san diego, a.k.a. M-7) which can be used to control coleopteran pests in various environments. U.S. Pat. No. 4,918,006 discloses Bacillus thuringiensis var. israelensis toxins which are active against dipteran pests. This patent reports that a protein of about 27 kD, and fragments thereof, are responsible for the dipteran activity. U.S. Pat. No. 4,849,217 discloses B.t. isolates which have activity against the alfalfa weevil. U.S. Pat. No. 5,151,363 and U.S. Pat. No. 4,948,734 disclose certain isolates of B.t. which have activity against nematodes.

The accepted methodology for control of nematodes has centered around the use of the drug benzimidazole and its congeners. The use of these drugs on a wide scale has led to many instances of resistance among nematode populations (Prichard et al., 1980; Coles, 1986). There are more than 100,000 described species of nematodes.

A small number of research articles have been published concerning the effects of .delta.-endotoxins from B. thuringiensis species on the viability of nematode eggs. Bottjer et al. (1985) have reported that B.t. kurstaki and B.t. israelensis were toxic in vitro to eggs of the nematode Trichostrongylus colubriformis. In addition, 28 other B.t. strains were tested with widely variable toxicities. The most potent had LD.sub.50 values in the nanogram range. Ignoffo and Dropkin (1977) have reported that the thermostable toxin from Bacillus thuringiensis (beta exotoxin) was active against a free-living nematode, Panagrellus redivivus (Goodey); a plant-parasitic nematode, Meloidogyne incognita (Chitwood); and a fungus-feeding nematode, Aphelenchus avena (Bastien). Beta exotoxin is a generalized cytotoxic agent with little or no specificity. Also, Ciordia and Bizzell (1961) gave a preliminary report on the effects of B. thuringiensis on some cattle nematodes.

At the present time there is a need to have more effective means to control the many nematodes that cause considerable damage to susceptible hosts. Effective means would advantageously employ biological agents, such as B.t. pesticides. As a result of extensive research and investment of resources, many other patents have issued for new B.t. isolates and new uses of B.t. isolates. However, the discovery of new B.t. isolates and new uses of known B.t. isolates remains an empirical, unpredictable art.

The subject invention concerns novel .delta.-endotoxin genes obtainable from B.t. isolates PS167P, PS80JJ1, PS158D5, PS169E, PS177F1, PS177G, PS204G4, and PS204G6, wherein the genes encode proteins which are active against nematode pests. These toxin genes can be transferred to suitable hosts as described herein.

Further aspects of the subject invention concern nematode-active toxins, and fragments thereof, encoded by the genes disclosed herein. Another embodiment of the subject invention concerns hosts transformed with the genes of the subject invention. In a preferred embodiment, the transformed hosts are plants.

FIG. 1 is a photograph of 9% SDS polyacrylamide gel electrophoresis showing alkali-soluble proteins of nematode active strains.

FIG. 1A: Lane(1) Protein standard,(2) PS17,(3) PS33F2,(4) PS52A1,(5) PS63B,(6), PS69D1,(7) PS80JJ1,(8) PS177F1,(9) PS177G,(10) PS204G6,(11) Protein standard.

FIG. 1B: Lane(1) Protein standard,(2) PS17,(3) PS33F2,(4) PS52A1,(5) PS63B,(6), PS69D1,(7) PS169E,(8) PS167P,(9) PS204G4,(10) PS158D5,(11) Protein standard.

SEQ ID NO.1 is the nucleotide sequence of a "forward" oligonucleotide primer used for PCR amplification of the 80JJ1 and 167P genes.

SEQ ID NO.2 is the nucleotide sequence of a "reverse" oligonucleotide primer used for PCR amplification of the 80JJ1 and 167P genes.

SEQ ID NO.3 is the nucleotide sequence of the 80JJ1 toxin gene.

SEQ ID NO.4 is the amino acid sequence of the 80JJ1 protein.

SEQ ID NO.5 is the nucleotide sequence of the 167P toxin gene.

SEQ ID NO.6 is the amino acid sequence of the 167P protein.

The subject invention pertains to novel genes which encode nematode-active toxins. The toxins themselves are also an important aspect of the invention. A further embodiment of the subject invention is the transformation of suitable hosts to confer upon these hosts the ability to express nematode-active toxins.

The Bacillus thuringiensis isolates from which the genes of the subject invention can be obtained have been deposited in the permanent collection of the Agricultural Research Service Patent Culture Collection (NRRL), Northern Regional Research Center, 1915 North University Street, Peoria, Ill. 61604, USA. The accession numbers are as follows:

The subject cultures have been deposited under conditions that assure that access to the cultures will be available during the pendency of this patent application to one determined by the Commissioner of Patents and Trademarks to be entitled thereto under 37 CFR 1.14 and 35 USC 122. The deposits are available as required by foreign patent laws in countries wherein counterparts of the subject application, or its progeny, are filed. However, it should be understood that the availability of the deposits does not constitute a license to practice the subject invention in derogation of patent rights granted by governmental action.

Further, the subject culture deposits will be stored and made available to the public in accord with the provisions of the Budapest Treaty for the Deposit of Microorganisms, i.e., they will be stored with all the care necessary to keep them viable and uncontaminated for a period of at least five years after the most recent request for the furnishing of a sample of a deposit, and in any case, for a period of at least 30 (thirty) years after the date of deposit or for the enforceable life of any patent which may issue disclosing the cultures. The depositor acknowledges the duty to replace the deposit(s) should the depository be unable to furnish a sample when requested, due to the condition of the deposit(s). All restrictions on the availability to the public of the subject culture deposits will be irrevocably removed upon the granting of a patent disclosing them.

Genes and toxins. The genes and toxins useful according to the subject invention include not only the full length sequences disclosed but also fragments of these sequences, variants, mutants, and fusion proteins which retain the characteristic pesticidal activity of the toxins specifically exemplified. In some instances, the fusion protein may contain, in addition to the characteristic pesticidal activity of the toxins specifically exemplified, another pesticidal activity contributed by the fusion process. As used herein, the terms "variants" or "variations" of genes refer to nucleotide sequences which encode the same toxins or which encode equivalent toxins having similar pesticidal activity. As used herein, the term "equivalent toxins" refers to toxins having the same or essentially the same biological activity against the target pests as the claimed toxins.

It should be apparent to a person skilled in this art that genes encoding nematode-active toxins can be identified and obtained through several means. The specific genes exemplified herein may be obtained from the isolates deposited at a culture depository as described above. These genes, or portions or variants thereof, may also be constructed synthetically, for example, by use of a gene synthesizer. Variations of genes may be readily constructed using standard techniques for making point mutations. Also, fragments of these genes can be made using commercially available exonucleases or endonucleases according to standard procedures. For example, enzymes such as Bal31 or site-directed mutagenesis can be used to systematically cut off nucleotides from the ends of these genes. Also, genes which encode active fragments may be obtained using a variety of restriction enzymes. Proteases may be used to directly obtain active fragments of these toxins.

Equivalent toxins and/or genes encoding these equivalent toxins can be derived from B.t. isolates and/or DNA libraries using the teachings provided herein. There are a number of methods for obtaining the pesticidal toxins of the instant invention. For example, antibodies to the pesticidal toxins disclosed and claimed herein can be used to identify and isolate other toxins from a mixture of proteins. Specifically, antibodies may be raised to the portions of the toxins which are most constant and most distinct from other B.t. toxins. These antibodies can then be used to specifically identify equivalent toxins with the characteristic activity by immunoprecipitation, enzyme linked immunosorbent assay (ELISA), or Western blotting. Antibodies to the toxins disclosed herein, or to equivalent toxins, or fragments of these toxins, can readily be prepared using standard procedures in this art. The genes which encode these toxins can then be obtained from the microorganism.

Fragments and equivalents which retain the pesticidal activity of the exemplified toxins would be within the scope of the subject invention. Also, because of the redundancy of the genetic code, a variety of different DNA sequences can encode the amino acid sequences disclosed herein. It is well within the skill of a person trained in the art to create these alternative DNA sequences encoding the same, or essentially the same, toxins. These variant DNA sequences are within the scope of the subject invention. As used herein, reference to "essentially the same" amino acid sequence refers to sequences which have amino acid substitutions, deletions, additions, or insertions which do not materially affect the pesticidal activity of the protein.

A further method for identifying the toxins and genes of the subject invention is through the use of oligonucleotide probes. These probes are nucleotide sequences having a means for detection. As is well known in the art, if the probe molecule and nucleic acid sample hybridize by forming a strong bond between the two molecules, it can be reasonably assumed that the probe and sample have substantial homology. The probe's means of detection provides a means for determining in a known manner whether hybridization has occurred. Such a probe analysis provides a rapid method for identifying toxin-encoding genes of the subject invention. The nucleotide segments which are used as probes according to the invention can be synthesized by use of DNA synthesizers using standard procedures. These nucleotide sequences can also be used as PCR primers to amplify genes of the subject invention.

Certain toxins of the subject invention have been specifically exemplified herein. Since these toxins are merely exemplary of the toxins of the subject invention, it should be readily apparent that the subject invention further comprises variant or equivalent toxins (and nucleotide sequences coding for equivalent toxins) having the same or essentially the same pesticidal activity of the exemplified toxins. These equivalent toxins can have amino acid homology with an exemplified toxin. This amino acid homology will typically be greater than 75%, preferably be greater than 90%, and most preferably be greater than 95%. The amino acid homology will be highest in certain critical regions of the toxin which account for biological activity or are involved in the determination of three-dimensional configuration which ultimately is responsible for the biological activity. In this regard, certain amino acid substitutions are acceptable and can be expected if these substitutions are in regions which are not critical to activity or are conservative amino acid substitutions which do not affect the three-dimensional configuration of the molecule. For example, amino acids may be placed in the following classes: non-polar, uncharged polar, basic, and acidic. Conservative substitutions whereby an amino acid of one class is replaced with another amino acid of the same type fall within the scope of the subject invention so long as the substitution does not materially alter the biological activity of the compound. Table 1 provides a listing of examples of amino acids belonging to each class.

In some instances, non-conservative substitutions can also be made. The critical factor is that these substitutions must not significantly detract from the biological activity of the toxin.

The toxins of the subject invention can also be characterized in terms of the shape and location of toxin inclusions.

Following is a table which provides characteristics of certain isolates useful according to the subject invention.

Recombinant hosts. The toxin-encoding genes harbored by the isolates of the subject invention can be introduced into a wide variety of microbial or plant hosts. Expression of the toxin gene results, directly or indirectly, in the intracellular production and maintenance of the pesticide. With suitable microbial hosts, e.g., Pseudomonas, the microbes can be applied to the situs of the pest, where they will proliferate and be ingested by the pest. The result is control of the pest. Alternatively, the microbe hosting the toxin gene can be treated under conditions that prolong the activity of the toxin and stabilize the cell. The treated cell, which retains the toxic activity, then can be applied to the environment of the target pest.

Where the B.t. toxin gene is introduced via a suitable vector into a microbial host, and said host is applied to the environment in a living state, it is advantageous to use certain host microbes. For example, microorganism hosts can be selected which are known to occupy the pest's habitat. Microorganism hosts may also live symbiotically with a specific species of pest. These microorganisms are selected so as to be capable of successfully competing in the particular environment with the wild-type microorganisms, provide for stable maintenance and expression of the gene expressing the polypeptide pesticide, and, desirably, provide for improved protection of the pesticide from environmental degradation and inactivation.

A large number of microorganisms are known to inhabit the habitat of pests. These microorganisms include bacteria, algae, and fungi. Of particular interest are microorganisms, such as bacteria, e.g., genera Pseudomonas, Erwinia, Serratia, Klebsiella, Xanthomonas, Streptomyces, Rhizobium, Rhodopseudomonas, Methylophilius, Agrobacterium, Acetobacter, Lactobacillus, Arthrobacter, Azotobacter, Leuconostoc, and Alcaligenes; fungi, e.g., genera Metarhizium, Bavaria, Saccharomyces, Cryptococcus, Kluyveromyces, Sporobolomyces, Rhodotorula, and Aureobasidium. Of particular interest are such bacterial species as Pseudomonas syringae, Pseudomonas fluorescens, Serratia marcescens, Acetobacter xylinum, Agrobacterium tumefaciens, Rhodopseudomonas spheroides, Xanthomonas campestris, Rhizobium melioti, Alcaligenes entrophus, and Azotobacter vinlandii; and yeast species such as Rhodotorula rubra, R. glutinis, R. marina, R. aurantiaca, Cryptococcus albidus, C. diffluens, C. laurentii, Saccharomyces rosei, S. pretoriensis, S. cerevisiae, Sporobolomyces roseus, S. odorus, Kluyveromyces veronae, and Aureobasidium pollulans. Of particular interest are the pigmented microorganisms.

A wide variety of ways are available for introducing a B.t. gene encoding a toxin into a microorganism host under conditions which allow for stable maintenance and expression of the gene. These methods are well known to those skilled in the art and are described, for example, in U.S. Pat. No. 5,135,867, which is incorporated herein by reference.

Control of nematodes using the isolates, toxins, and genes of the subject invention can be accomplished by a variety of methods known to those skilled in the art. These methods include, for example, the application of B.t. isolates to the pests (or their location), the application of recombinant microbes to the pests (or their locations), and the transformation of plants with genes which encode the pesticidal toxins of the subject invention. Recombinant microbes may be, for example, a B.t., E. coli, or Pseudomonas. Transformations can be made by those skilled in the art using standard techniques. Materials necessary for these transformations are disclosed herein or are otherwise readily available to the skilled artisan. For example, the gene encoding the 167P toxin is provided herein as SEQ ID NO.5. The deduced amino acid sequence for the 167P toxin is provided in SEQ ID NO.6.

Treatment of cells. As mentioned above, B.t. or recombinant cells expressing a B.t. toxin can be treated to prolong the toxin activity and stabilize the cell. The pesticide microcapsule that is formed comprises the B.t. toxin within a cellular structure that has been stabilized and will protect the toxin when the microcapsule is applied to the environment of the target pest. Suitable host cells may include either prokaryotes or eukaryotes, normally being limited to those cells which do not produce substances toxic to higher organisms, such as mammals. However, organisms which produce substances toxic to higher organisms could be used, where the toxic substances are unstable or the level of application sufficiently low as to avoid any possibility of toxicity to a mammalian host. As hosts, of particular interest will be the prokaryotes and the lower eukaryotes, such as fungi.

The cell will usually be intact and be substantially in the proliferative form when treated, rather than in a spore form, although in some instances spores may be employed.

Treatment of the microbial cell, e.g., a microbe containing the B.t. toxin gene, can be by chemical or physical means, or by a combination of chemical and/or physical means, so long as the technique does not deleteriously affect the properties of the toxin, nor diminish the cellular capability of protecting the toxin. Examples of chemical reagents are halogenating agents, particularly halogens of atomic no. 17-80. More particularly, iodine can be used under mild conditions and for sufficient time to achieve the desired results. Other suitable techniques include treatment with aldehydes, such as glutaraldehyde; anti-infectives, such as zephiran chloride and cetylpyridinium chloride; alcohols, such as isopropyl and ethanol; various histologic fixatives, such as Lugol iodine, Bouin's fixative, various acids, and Helly's fixative (See: Humason, 1967); or a combination of physical (heat) and chemical agents that preserve and prolong the activity of the toxin produced in the cell when the cell is administered to the host animal. Examples of physical means are short wavelength radiation such as gamma-radiation and X-radiation, freezing, UV irradiation, lyophilization, and the like. Methods for treatment of microbial cells are disclosed in U.S. Pat. Nos. 4,695,455 and 4,695,462, which are incorporated herein by reference.

The cells generally will have enhanced structural stability which will enhance resistance to environmental conditions. Where the pesticide is in a proform, the method of cell treatment should be selected so as not to inhibit processing of the proform to the mature form of the pesticide by the target pest pathogen. For example, formaldehyde will crosslink proteins and could inhibit processing of the proform of a polypeptide pesticide. The method of cell treatment retains at least a substantial portion of the bio-availability or bioactivity of the toxin.

Characteristics of particular interest in selecting a host cell for purposes of production include ease of introducing the B.t. gene into the host, availability of expression systems, efficiency of expression, stability of the pesticide in the host, and the presence of auxiliary genetic capabilities. Characteristics of interest for use as a pesticide microcapsule include protective qualities for the pesticide, such as thick cell walls, pigmentation, and intracellular packaging or formation of inclusion bodies; survival in aqueous environments; lack of mammalian toxicity; attractiveness to pests for ingestion; ease of killing and fixing without damage to the toxin; and the like. Other considerations include ease of formulation and handling, economics, storage stability, and the like.

Growth of cells. The cellular host containing the B.t. insecticidal gene may be grown in any convenient nutrient medium, where the DNA construct provides a selective advantage, providing for a selective medium so that substantially all or all of the cells retain the B.t. gene. These cells may then be harvested in accordance with conventional ways. Alternatively, the cells can be treated prior to harvesting.

The B.t. cells of the invention can be cultured using standard art media and fermentation techniques. Upon completion of the fermentation cycle the bacteria can be harvested by first separating the B.t. spores and crystals from the fermentation broth by means well known in the art. The recovered B.t. spores and crystals can be formulated into a wettable powder, liquid concentrate, granules or other formulations by the addition of surfactants, dispersants, inert carriers, and other components to facilitate handling and application for particular target pests. These formulations and application procedures are all well known in the art and are used with commercial strains of B. thuringiensis (HD-1) active against Lepidoptera, e.g., caterpillars. The B.t. isolates (spores and crystals) of the subject invention can be used to control nematode pests.

The B.t. toxins of the invention can be administered orally in a unit dosage form such as a capsule, bolus or tablet, or as a liquid drench when used as an anthelmintic in mammals. The drench is normally a solution, suspension or dispersion of the active ingredient, usually in water, together with a suspending agent such as bentonite and a wetting agent or like excipient. Generally, the drenches also contain an antifoaming agent. Drench formulations generally contain from about 0.001 to 0.5% by weight of the active compound. Preferred drench formulations may contain from 0.01 to 0.1% by weight, the capsules and boluses comprise the active ingredient admixed with a carrier vehicle such as starch, talc, magnesium stearate, or dicalcium phosphate.

Where it is desired to administer the toxin compounds in a dry, solid unit dosage form, capsules, boluses or tablets containing the desired amount of active compound usually are employed. These dosage forms are prepared by intimately and uniformly mixing the active ingredient with suitable finely divided diluents, fillers, disintegrating agents and/or binders such as starch, lactose, talc, magnesium stearate, vegetable gums and the like. Such unit dosage formulations may be varied widely with respect to their total weight and content of the nematode-active agent, depending upon the factors such as the type of host animal to be treated, the severity and type of infection and the weight of the host.

When the active compound is to be administered via an animal feedstuff, it is intimately dispersed in the feed or used as a top dressing or in the form of pellets which may then be added to the finished feed or, optionally, fed separately. Alternatively, the compounds may be administered to animals parenterally, for example, by intraluminal, intramuscular, intratracheal, or subcutaneous injection, in which event the active ingredient is dissolved or dispersed in a liquid carrier vehicle. For parenteral administration, the active material is suitably admixed with an acceptable vehicle, preferably of the vegetable oil variety, such as peanut oil, cotton seed oil and the like. Other parenteral vehicles, such as organic preparations using solketal, glycerol, formal and aqueous parenteral formulations, are also used. The active compound or compounds are dissolved or suspended in the parenteral formulation for administration; such formulations generally contain from 0.005 to 5% by weight of the active compound.

When the toxins are administered as a component of the feed of the animals, or dissolved or suspended in the drinking water, compositions are provided in which the active compound or compounds are intimately dispersed in an inert carrier or diluent. By inert carrier is meant one that will not react with the nematode-active agent and one that may be administered safely to animals. Preferably, a carrier for feed administration is one that is, or may be, an ingredient of the animal ration.

Suitable compositions include feed premixes or supplements in which the active ingredient is present in relatively large amounts and which are suitable for direct feeding to the animal or for addition to the feed either directly or after an intermediate dilution or blending step. Typical carriers or diluents suitable for such compositions include, for example, distillers' dried grains, corn meal, citrus meal, fermentation residues, ground oyster shells, wheat shorts, molasses solubles, corn cob meal, edible bean mill feed, soya grits, crushed limestone and the like.

In addition to having anthelminthic activity within the digestive tract of mammals, spores from nematicidal B.t. isolates will pass through the animals' digestive tract, germinate and multiply in the feces, and thereby provide additional control of nematode larva which hatch and multiply therein.

As would be appreciated by a person skilled in the art, the pesticidal concentration will vary widely depending upon the nature of the particular formulation, particularly whether it is a concentrate or to be used directly. The pesticide will be present in at least 1% by weight and may be 100% by weight. The dry formulations will have from about 1-95% by weight of the pesticide while the liquid formulations will generally be from about 1-60% by weight of the solids in the liquid phase. The formulations will generally have from about 10.sup.2 to about 10.sup.4 cells/mg. These formulations will be administered at about 50 mg (liquid or dry) to 1 kg or more per hectare.

The formulations can be applied to the environment of the nematode pests, e.g., plants, soil, or water by spraying, dusting, sprinkling, or the like.

Mutants. Mutants of the B.t. isolates of the subject invention can be made by procedures well known in the art. For example, an asporogenous mutant can be obtained through ethylmethane sulfonate (EMS) mutagenesis. The mutants can be made using ultraviolet light and nitrosoguanidine by procedures well known in the art.

A smaller percentage of the asporogenous mutants will remain intact and not lyse for extended fermentation periods; these strains are designated lysis minus (-). Lysis minus strains can be identified by screening asporogenous mutants in shake flask media and selecting those mutants that are still intact and contain toxin crystals at the end of the fermentation. Lysis minus strains are suitable for a cell treatment process that will yield a protected, encapsulated toxin protein.

To prepare a phage resistant variant of said asporogenous mutant, an aliquot of the phage lysate is spread onto nutrient agar and allowed to dry. An aliquot of the phage sensitive bacterial strain is then plated directly over the dried lysate and allowed to dry. The plates are incubated at 30.degree. C. The plates are incubated for 2 days and, at that time, numerous colonies could be seen growing on the agar. Some of these colonies are picked and subcultured onto nutrient agar plates. These apparent resistant cultures are tested for resistance by cross streaking with the phage lysate. A line of the phage lysate is streaked on the plate and allowed to dry. The presumptive resistant cultures are then streaked across the phage line. Resistant bacterial cultures show no lysis anywhere in the streak across the phage line after overnight incubation at 30.degree. C. The resistance to phage is then reconfirmed by plating a lawn of the resistant culture onto a nutrient agar plate. The sensitive strain is also plated in the same manner to serve as the positive control. After drying, a drop of the phage lysate is plated in the center of the plate and allowed to dry. Resistant cultures showed no lysis in the area where the phage lysate has been placed after incubation at 30.degree. C. for 24 hours.

Following are examples which illustrate procedures, including the best mode, for practicing the invention. These examples should not be construed as limiting. All percentages are by weight and all solvent mixture proportions are by volume unless otherwise noted.

A subculture of a B.t. strain can be used to inoculate the following medium, a peptone, glucose, salts medium.

The salts solution and CaCl.sub.2 solution are filter-sterilized and added to the autoclaved and cooked broth at the time of inoculation. Flasks are incubated at 30.degree. C. on a rotary shaker at 200 rpm for 64 hr.

The above procedure can be readily scaled up to large fermentors by procedures well known in the art.

The B.t. spores and crystals, obtained in the above fermentation, can be isolated by procedures well known in the art. A frequently-used procedure is to subject the harvested fermentation broth to separation techniques, e.g., centrifugation.

Worms were collected in a tube and allowed to settle for about 15 minutes. The water was decanted and replaced with fresh water three or four times until the water remained clear. 250 .mu.l rinsed nematodes (20-30 worms), and 100 .mu.l of a spore/crystal suspension were added to 650 .mu.l water in each well of a multi-well tray. Nematodes were counted and the numbers recorded. After four days, the live worms were counted and percent mortality calculated.

Tables 4 and 5 show the molecular mass of the alkali-soluble proteins in each novel nematode-active strain, as compared to previously known B.t. strains.

Total cellular DNA was prepared from Bacillus thuringiensis (B.t. ) cells grown to an optical density, at 600 nm, of 1.0. Cells were pelleted by centrifugation and resuspended in protoplast buffer (20 mg/ml lysozyme in 0.3 M sucrose, 25 mM Tris-Cl (pH 8.0), 25 mM EDTA). After incubation at 37.degree. C. for 1 hour, protoplasts were lysed by two cycles of freezing and thawing. Nine volumes of a solution of 0.1 M NaCl, 0.1% SDS, 0.1 M Tris-Cl were added to complete lysis. The cleared lystate was extracted twice with phenol:chloroform (1:1). Nucleic acids were precipitated with two volumes of ethanol and pelleted by centrifugation. The pellet was resuspended in TE buffer and RNase was added to a final concentration of 50 .mu.g/ml. After incubation at 37.degree. C. for 1 hour, the solution was extracted once each with phenol:chloroform (1:1) and TE-saturated chloroform. DNA was precipitated from the aqueous phase by the addition of one-tenth volume of 3 M NaOAc and two volumes of ethanol. DNA was pelleted by centrifugation, washed with 70% ethanol, dried, and resuspended in TE buffer.

An approximately 700-800 bp DNA fragment from a novel PS80JJ1 130 kDa toxin gene was obtained by polymerase chain reaction (PCR) amplification using PS80JJ1 cellular DNA and the following primers:

The DNA fragment was cloned into pBluescript S/K (Stratagene, LaJolla, Calif.) and partially sequenced by dideoxynucleotide DNA sequencing methodology (Sanger et al., 1977) using Sequenase (US Biochemicals, Cleveland, Ohio). DNA sequences unique to at least one PS80JJ1 toxin gene were identified by computer comparison with other known .delta.-endotoxin genes.

The 700-800 bp DNA fragment was radiolabelled with .sup.32 P and used in standard hybridizations of Southern blots of PS80JJ1 total cellular DNA. Hybridizing bands included an approximately 1.8 kbp EcoRI fragment and an approximately 9.5 kbp HindIII fragment. These hybridizing DNA bands contain toxin genes or restriction fragments of toxin genes from PS80JJ1.

A gene library was constructed from PS80JJ1 DNA partially digested with NdeII. Partial restriction digests were fractionated by agarose gel electrophoresis. DNA fragments 9.3 to 23 kbp in size were excised from the gel, electroeluted from the gel slice, purified on an Elutip-D ion exchange column (Schleicher and Schuell, Keene, N.H.), and recovered by ethanol precipitation. The NdeII inserts were ligated into BamHI-digested LambdaGem-11 (Promega, Madison, Wis.). Recombinant phage were packaged and plated on E. coli KW251 cells. Plaques were screened by hybridization with the probe described above. Hybridizing phage were plaque-purified and used to infect liquid cultures of E. coli KW251 cells for isolation of DNA by standard procedures (Maniatis et al.).

For subcloning the gene encoding the PS80JJ1 130 kDa toxin, preparative amounts of phage DNA were digested with XhoI and electrophoresed on an agarose gel. The approximately 12 kbp band containing the toxin gene was excised from the gel, electroeluted from the gel slice, and purified by ion exchange chromatography as described above. The purified DNA insert was ligated into XhoI-digested pHTBlueII (an E. coli/B. thuringiensis shuttle vector comprised of pBluescript S/K ›Stratagene, La Jolla, Calif.! and the replication origin from a resident B.t. plasmid ›Lereclus et al. !). The ligation mix was used to transform frozen, competent E. coli NM522 cells (ATCC 47000). .beta.-galactosidase-transformants were screened by restriction digestion of alkaline lysate plasmid minipreps as above. The desired plasmid construct, pMYC2379, contains a toxin gene that is novel compared to other toxin genes containing insecticidal proteins.

The PS80JJ1 toxin gene encoded by pMYC2379 was sequenced using the ABI373 automated sequencing system and associated software. Sequence analysis of the toxin gene revealed that it encodes a protein of approximately 130,000 daltons, deduced from the DNA sequence. The nucleotide and deduced amino acid sequences are shown in SEQ ID NOS. 3 and 4, respectively.

pMYC2379 was introduced into the acrystalliferous (Cry.sup.-) B.t. host, CryB (A. Aronson, Purdue University, West Lafayette, Ind.), by electroporation. Expression of the 130 kDa toxin was demonstrated by SDS-PAGE analysis.

A subculture of E. coli NM522 containing plasmid pMYC2379 was deposited in the permanent collection of the Patent Culture Collection (NRRL), Regional Research Center, 1815 North University Street, Peoria, Ill. 61604 USA or Nov. 3, 1991. The accession number is NRRL B-21155.

Total cellular DNA was prepared as in Example 3.

An approximately 700-800 bp DNA fragment from novel PS167P 130 kDa toxin genes was obtained by polymerase chain reaction (PCR) amplification using PS167P cellular DNA and SEQ ID NOS. 1 and 2. This DNA fragment was cloned into pBluescript S/K (Stratagene, La Jolla, Calif.) and partially sequenced by dideoxynucleotide DNA sequencing methodology (Sanger et al., 1977) using Sequenase (U.S. Biochemicals, Cleveland, Ohio). DNA sequences unique to at least two PS167P toxin genes were identified by computer comparison with other known .delta.-endotoxin genes.

The 700-800 bp DNA fragment was radiolabelled with .sup.32 P and used in standard hybridizations of Southern blots of PS167P total cellular DNA. Hybridizing bands included approximately 1.8 kbp and 2.3 kbp EcoRI fragments and approximately 5.5 kbp and 8.0 kbp HindIII fragments. These DNA fragments contain toxin genes or restriction fragments of toxin genes unique to PS167P.

A gene library was constructed from PS167P DNA partially digested with NdeII. Partial restriction digests were fractionated by agarose gel electrophoresis. DNA fragments 9.3 to 23 kbp in size were excised from gel, electroeluted from the gel slice, purified on an Elutip-D ion exchange column (Schleicher and Schuell, Keene, N.H.), and recovered by ethanol precipitation. The NdeII inserts were ligated into BamHI-digested LambdaGem-11 (Promega, Madison, Wis.). Recombinant phage were packaged and plated on E. coli KW251 cells. Plaques were screened by hybridization with the probe described above. Hybridizing phage were plaque-purified and used to infect liquid cultures of E. coli KW251 cells for isolation of DNA by standard procedures (Maniatis et al, 1989).

Southern blot analysis revealed that one of the recombinant phage isolates contained an approximately 5 kbp SalI band that hybridized to the PS167P toxin gene probe. One of the SalI sites flanking the PS167P toxin gene resides in the phage vector DNA sequence, while the other flanking SalI site is located within the PS167P DNA insert. This SalI fragment was subcloned by standard methods into pBluescript S/K (Stratagene, San Diego, Calif.) for DNA sequence analysis. The DNA insert was subcloned further as a SacI-KpnI fragment into pHTBlueII (an E. coli/B. thuringiensis shuttle vector comprised of pBluescript S/K and the replication origin from a resident B.t. plasmid ›Lereclus et al., 1989! to yield pMYC2382. To test expression of the PS167P toxin gene in B.t. , pMYC2382 was introduced into the acrystalliferous (Cry-) B.t. host, CryB (A. Aronson, Purdue University, West Lafayette, Ind.) by electroporation. Expression of the approximately 130 kDa PS167P toxin encoded by pMYC2382 was demonstrated by SDS-PAGE analysis.

The PS167P toxin gene encoded by pMYC2382 was sequenced using the ABI373 automated sequencing system and associated software. The PS167P toxin nucleotide (SEQ ID NO.5) and deduced amino acid (SEQ ID NO.6) sequences are novel compared to other toxin genes encoding pesticidal proteins.

A subculture of E. coli NM522 containing plasmid pMYC2382 was deposited in the permanent collection of the Patent Culture Collection (NRRL), Regional Research Center, 1815 North University Street, Peoria, Ill. 61604 USA on Sep. 28, 1994. The accession number is NRRL B-21329.

One aspect of the subject invention is the transformation of plants with genes encoding a toxin active against nematode pests. The transformed plants are resistant to attack by nematodes.

Genes encoding pesticidal toxins, as disclosed herein, can be modified for optimum expression in plant, linked to a plant selectable marker gene, and inserted into a genome of plant cell using a variety of techniques which are well known to those skilled in the art. Any plant may be used in accordance with this invention, including angiosperms, gymnosperms, monocotyledons and dicotyledons. Preferred plants include soybean, sunflower, cotton, potato, alfalfa, maize, rice and wheat. The transformation method itself is not critical to the invention but may include transformation with T-DNA using Agrobacterium tumefaciens or A. rhizogenes as the transformation agent, liposome fusion, microinjection, microprojectile bombardment, chemical agent (PEG or calcium chloride)-assisted DNA uptake, or electroporation, as well as other possible methods. Reference may be made to the literature for full details of the known methods, especially Holsters et al., 1978; Fromm et al., 1985; Horsch et al., 1985; Herrera-Estrella et al., 1983; Crossway et al., 1986; Lin, 1966; and Steinkiss and Stabel, 1983.

Use of a plant selectable marker in transformation allows for selection of transformed cells rather than cells that do not contain the inserted DNA. Various markers exist for use in plant cells and generally provide resistance to a biocide or antibiotic, including but not limited to, kanamycin, G418, hygromycin, and phosphinothricin. Visual markers including but not limited to b-glucuronidase, b-galactosidase, B-peru protein, green fluorescent protein, and luciferase may also be used. After transformation, those cells that have the DNA insert can be selected for by growth in a defined medium and assayed for marker expression, whether by resistance or visualization. Cells containing the DNA insert can be regenerated into plants. As long as stably transformed plants are obtained, the method used for regeneration will depend on the plant tissue and transformation method used and is not critical to the invention. However, for example, where cell suspensions have been used for transformation, transformed cells can be induced to produce calli and the calli subsequently induced to form shoots, which may then be transferred to an appropriate nutrient medium to regenerate plants. Alternatively, explants such as hypocotyl tissue or embryos may be transformed and regenerated by shoot induction in the appropriate media, followed by root and whole plant formation. Whatever regeneration method is used, the result will be stably transformed plants that can vegetatively and sexually transmit the transformed trait(s) to progeny, so that, if necessary, the transformed plant can be crossed with untransformed plants in order to transfer the trait to more appropriate germplasm for breeding purposes.

A number of viruses are known to infect insects. These viruses include, for example, baculoviruses and entomopoxviruses. In one embodiment of the subject invention, nematode-active genes, as described herein, can be placed with the genome of the insect virus, thus enhancing the pathogenicity of the virus. Methods for constructing insect viruses which comprise B.t. toxin genes are well known and readily practiced by those skilled in the art. These procedures are described, for example, in Merryweather et al. (1990) and Martens et al. (1990).

It should be understood that the examples and embodiments described herein are for illustrative purposes only and that various modifications or changes in light thereof will be suggested to persons skilled in the art and are to be included within the spirit and purview of this application and the scope of the appended claims.

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