Transformation of Bacillus thuringiensis protoplasts by plasmid deoxyribonucleic acid

Transformation of Bacillus thuringiensis plasmid DNA by a new polyethylenimine polymeric nanoparticles method

Although electroporation technique has been mostly used to transform Bacillus thuringiensis (Bt), this method is not readily applicable to strains other than the one for which it was optimized. Polyethylenimine (PEI) is a golden standard non-viral vector that interacts with plasmids to form compact polymeric nanoparticles (PNPs) via electrostatic interactions. This PNPs system is very attractive because they are easily prepared, able to carry large nucleic acid constructs, and show low toxicity. In this study, PEI/pBTdsSBV-VP1 PNPs were successfully prepared at various N/P ratios which is positively-chargeable polymer amine (N = nitrogen) groups to negatively-charged nucleic acid phosphate (P) groups, and the internalization of the complexes into Bt 4Q7 was confirmed by confocal laser scanning microscopy. The PEI-mediated transformation showed similar efficiency comparable to that of electroporation method, suggesting that the method of PNPs will be an effective alternative for transformation of Bt strains.

Characterization, kinetics and thermodynamics of biosynthesized uranium nanoparticles (UNPs)

The present study was carried out to explore the potential of the isolated bacterial strains isolated from Gabal El Sela in Eastern Dessert, Egypt for biosynthesis of uraninite nanoparticles intracellularly. The most potent bacterial strains associated (intra) with uranium nanoparticles were characterized by transmission electron microscope (TEM), Fourier transform infrared (FTIR) and Energy Dispersive X-ray (EDX). Studying factors affecting biosynthesis of uranium nanoparticles indicated that the optimum conditions were 6000 ppm uranium concentrations at pH 7.0 and temperature 30 °C ± 1 after five days with 10% biomass under shaking conditions and the maximum uranium uptake by MAM - U9 cells was 3300 ppm (55%) from uranyl nitrate solution and 3600 ppm (72%) from Sela rock sample. Results of TEM micrograph show those uranium nanoparticles (UNPs) with size ranging from 2.9 to 21.13 nm inside cells. The kinetics, isotherm and thermodynamics parameters of uranium uptaken by bacterial strain MAM -U9 have been determined and found to be a first order process (R² = 9935), follows Langmuir isotherm (R_L² = 0.998) and the thermodynamics of ΔG = -9.715 kJmol^-1, ΔH = 16.987 kJmol^-1 and ΔS = 0.0881 kJmol^-1K^-1 at 30 °C.

PhoR/PhoP two component regulatory system affects biocontrol capability of Bacillus subtilis NCD-2

The Bacillus subtilis strain NCD-2 is an important biocontrol agent against cotton verticillium wilt and cotton sore shin in the field, which are caused by Verticillium dahliae Kleb and Rhizoctonia solani Kuhn, respectively. A mutant of strain NCD-2, designated M216, with decreased antagonism to V. dahliae and R. solani, was selected by mini-Tn10 mutagenesis and in vitro virulence screening. The inserted gene in the mutant was cloned and identified as the phoR gene, which encodes a sensor kinase in the PhoP/PhoR two-component system. Compared to the wild-type strain, the APase activities of the mutant was decreased significantly when cultured in low phosphate medium, but no obvious difference was observed when cultured in high phosphate medium. The mutant also grew more slowly on organic phosphate agar and lost its phosphatidylcholine-solubilizing ability. The suppression of cotton seedling damping-off in vivo and colonization of the rhizosphere of cotton also decreased in the mutant strain when compared with the wild type strain. All of these characteristics could be partially restored by complementation of the phoR gene in the M216 mutant.

New yeast recombineering tools for bacteria

Recombineering with Saccharomyces cerevisiae is a powerful methodology that can be used to clone multiple unmarked pieces of DNA to generate complex constructs with high efficiency. Here, we introduce two new tools that utilize the native recombination enzymes of S. cerevisiae to facilitate the manipulation of DNA. First, yeast recombineering was used to make directed nested deletions in a bacteria-yeast shuttle plasmid using only one or two single stranded oligomers, thus obviating the need for a PCR step. Second, we have generated several new shuttle vectors for yeast recombineering capable of replication in a wide variety of bacterial genera. As a demonstration of utility, some of the approaches and vectors generated in this study were used to make a pigP deletion mutation in the opportunistic pathogen Serratia marcescens.

Isolation of Tn916-like conjugal elements from swine lot effluent

Isolates of Enterococcus faecalis obtained from a swine farrowing house outflow were examined for genetic elements similar to Tn916. Of the enterococci isolated, 71% were resistant to tetracycline. Among the tetracycline-resistant enterococci isolated from the outflow samples, approximately 34% were able to transfer the tetracycline resistance phenotype to Bacillus thuringiensis in cross-genus matings. The frequencies of transfer for 10 random isolates were comparable to those for transfer of Tn916 from E. faecalis to B. thuringiensis. In addition, these elements were shown to mobilize plasmid pC194 between Bacillus species, as did Tn916. Southern blot and polymerase chain reaction (PCR) analysis showed these elements share extensive structural homology with Tn916. The selected conjugal elements were capable of transfer to a Bacillus recipient in a soil environment. When the swine waste was introduced into the soil, the tetracycline resistant fecal enterococci levels rose from essentially undetectable levels to approximately 4 x 10(4) and remained at this level for 4 weeks. After six months, including one winter, levels had decreased to 5 x 10(3).

The construction of Bacillus thuringiensis strains expressing novel entomocidal delta-endotoxin combinations

Using our recently reported method of electroporation to transform Bacillus thuringiensis [Bone & Ellar (1989) FEMS Microbiol. Lett. 58, 171-178], cloned B. thuringiensis entomocidal delta-endotoxin genes have been introduced into several native B. thuringiensis strains. In many cases the resulting transformants expressed both their native toxins and the cloned toxin, producing strains with broader toxicity spectra. The introduction of the var. tenebrionis toxin gene into B. thuringiensis var. israelensis resulted in a strain with activity against Pieris brassicae (cabbage white butterfly), an activity which neither parent strain possesses. We discuss further the possibility of synergism and also the problems associated with introducing cloned DNA by this method.

Transformation of Bacillus polymyxa with plasmid DNA

A plasmid transformation system was developed for Bacillus polymyxa ATCC 12321 and derivatives of this strain. The method utilizes a penicillin-treated-cell technique to facilitate uptake of the plasmid DNA. Low-frequency transformation (10(-6) per recipient cell) of plasmids pC194, pBD64, and pBC16 was accomplished with this method. Selection for the transformants was accomplished on both hypertonic and nonhypertonic selective media, with the highest rates of recovery occurring on a peptone-glucose-yeast extract medium containing 0.25 M sucrose. Several additional plasmids were shown to be capable of transferring their antibiotic resistance phenotypes to B. polymyxa through the use of a protoplast transformation procedure which allowed for a more efficient transfer of the plasmid DNA. However, cell walls could not be regenerated on the transformed protoplasts, and the transformants could not be subcultured from the original selective media.

Efficient transformation of Bacillus thuringiensis and B. cereus via electroporation: transformation of acrystalliferous strains with a cloned delta-endotoxin gene

Electroporation was used as a method to transform intact cells of Bacillus thuringiensis and B. cereus. With our optimized method a range of plasmid vectors could be transformed into strains of B. thuringiensis at frequencies of up to 10(7) transformants/micrograms DNA. This high frequency allows cloning experiments to be done directly in B. thuringiensis. A bifunctional vector capable of replicating in Escherichia coli and in Bacillus spp. was constructed. The kurhd1 protoxin gene was cloned into this shuttle vector to produce plasmid pX193, then transformed into B. thuringiensis HD1 cryB and B. cereus 569K. The cloned protoxin gene was expressed in sporulating cultures of both strain HD1 cryB (pX193) and 569K (pXI93), producing crystal protein active in biotests against larvae of Heliothis virescens. This demonstrates the usefulness of the electroporation method for the introduction of cloned toxin genes, in either their native or modified form, into a variety of host strains.

Transformation of Bacillus cereus vegetative cells by electroporation

Transformation of untreated vegetative cells of Bacillus cereus 569 with plasmid pC194 (1.8 megadaltons) by high-voltage electroporation resulted in a maximum of 2 x 10(-5) transformants per viable cell. Transformation of a 130-megadalton plasmid occurred at a comparable frequency. The method was simple, rapid, and yielded transformant colonies in 14 to 24 h. Transformation was obtained with unpurified total plasmid DNA.

Tn916-dependent conjugal transfer of PC194 and PUB110 from Bacillus subtilis into Bacillus thuringiensis subsp. israelensis

The Staphylococcus aureus plasmids pC194 and pUB110 were introduced into Bacillus thuringiensis subsp. israelensis by using the Streptococcus faecalis transposon Tn916 as a mobilizing agent. Plasmid transfer occurred only when B. thuringiensis subsp. israelensis was mated with a B. subtilis donor that contained both pC194 and pUB110 and Tn916; plasmid transfer was not observed in the absence of the transposon. B. thuringiensis transconjugants resistant to chloramphenicol (Cmr) and tetracycline (Tetr) were detected at a frequency of 1.96 x 10(-6) per recipient cell, whereas the Tetr phenotype, but not the Cmr, was observed at a frequency of 1.09 x 10(-4). The converse, Cmr but not Tetr, was observed at a frequency of 2.94 X 10(-5). The transfer of pUB110 from B. subtilis to B. thuringiensis subsp. israelensis was observed at a frequency of 3.0 x 10(-6) per recipient cell but concomitant transfer of pUB110 and Tn916 was not observed. Mobilization of plasmid pE194 was not observed under these conditions. Transconjugants were detected in filter matings only, not in broth. The Tn916 phenotype was maintained during serial passage of B. thuringiensis without selection, whereas the pC194 phenotype was not. Unlike pC194, however, pUB110 remained stable in B. thuringiensis during several passages through nonselective medium. Southern hybridization analysis demonstrated that Tn916 had inserted into several different sites on the B. thuringiensis chromosome and that pC194 and pUB110 were maintained as an autonomous plasmid.

Introduction of the Streptococcus faecalis transposon Tn916 into Bacillus thuringiensis subsp. israelensis

The conjugative Streptococcus faecalis transposon Tn916 was introduced into Bacillus thuringiensis subsp. israelensis by filter matings with S. faecalis. B. thuringiensis transconjugants resistant to tetracycline (Tetr) were detected at a frequency of approximately 7.0 X 10(-7) per recipient cell during filter matings, whereas transfer of Tn916 was not observed in broth matings. The Tetr phenotype in subsp. israelensis was stable in the absence of antibiotic selection. Southern hybridization analysis revealed that Tn916 had inserted into several different sites on the B. thuringiensis subsp. israelensis chromosome but insertion into plasmid DNA was not observed. Movement of Tn916 was demonstrated when Tetr B. thuringiensis transconjugants were mated with isogenic recipients. Southern hybridizations, however, showed that the resulting Tetr isolates contained Tn916 junction fragments that were nearly identical to the donor, suggesting that this movement resulted from transfer of chromosomal DNA from donor to recipient or from a fusion of mating cells, rather than conjugative transposition of the Tn element.

Facile autoplast generation and transformation in Bacillus thuringiensis subsp. kurstaki

We describe a method for maximizing the rate of conversion of Bacillus thuringiensis subsp. kurstaki vegetative cells to osmotically fragile forms in the absence of exogenously added enzymes. Optimal generation of autoplasts occurred in 50 mM sodium acetate buffer (pH 7.0) at 37 degrees C with 10% (wt/vol) polyethylene glycol as an osmotic stabilizer. The maximum autolytic rate resulted in a conversion of greater than 90% of bacilli to spherical autoplasts in 6 min. Autoplasts regained bacillary morphology upon plating on DM3-G regeneration medium, with reversion frequencies ranging from 1.2 x 10(-1) to 5.3 x 10(-3). The autoplasts could efficiently take up exogenously added plasmid DNA. The presence of plasmids was verified by Southern hybridization analysis.

Transformation of vegetative cells of Bacillus thuringiensis by plasmid DNA

Plasmid DNA-mediated transformation of vegetative cells of Bacillus thuringiensis was studied with the following two plasmids: pBC16 coding for tetracycline resistance and pC194 expressing chloramphenicol resistance. A key step was the induction of competence by treatment of the bacteria with 50 mM Tris hydrochloride buffer (pH 8.9) containing 30% sucrose. Transformation frequency was strongly influenced by culture density during the uptake of DNA and required the presence of polyethylene glycol. Growth in a minimal medium supplemented with Casamino Acids gave 35 times more transformants than growth in a rich medium. The highest frequencies were obtained with covalently closed circular DNA. With all parameters optimized, the frequency was 10(-3) transformants per viable cell or 10(4) transformants per microgram of DNA. Cells previously frozen were also used as recipients in transformation experiments; such cells gave frequencies similar to those obtained with freshly grown cells. The procedure was optimized for B. thuringiensis subsp. gelechiae, but B. thuringiensis subsp. kurstaki, B. thuringiensis subsp. galleriae, B. thuringiensis subsp. thuringiensis, and B. thuringiensis subsp. israelensis were also transformed. Compared with protoplast transformation, our method is much faster and 3 orders of magnitude more efficient per microgram of added DNA.

The biotechnology of Bacillus thuringiensis

One of the challenges in the application of biotechnology to pest control is the identification of agents found in nature which can be used effectively. Biotechnology offers the potential of developing pesticides based on such agents which will provide environmentally sound and economically feasible insect control alternatives. Such an agent, the insect pathogen Bacillus thuringiensis, is the subject of intense investigations in several laboratories. Insecticides which use the entomocidal properties of B. thuringiensis are currently produced and sold worldwide; new products are currently in the development stage. Herein, the biology and genetics of B. thuringiensis and the problems associated with current products are critically reviewed with respect to biotechnology. Moreover, the economic and regulatory implications of technologically advanced products are evaluated.

Bacillus thuringiensis and related insect pathogens

Images

Introduction of plasmid pC194 into Bacillus thuringiensis by protoplast transformation and plasmid transfer

The Staphylococcus aureus plasmid pC194 which codes for resistance to chloramphenicol was introduced into six Bacillus thuringiensis strains representing five varieties by protoplast transformation. Six other varieties could not be transformed. pC194 could be identified in transformed strains as autonomous plasmid. The transformed clones contained in addition a new extrachromosomal element of somewhat lower electrophoretic mobility hybridizing with pC194, and pC194 in multimeric forms. pC194 was also transferred from one B. thuringiensis variety to another and from Bacillus thuringiensis to Bacillus subtilis and vice versa by a conjugation-like process, requiring close cell-to-cell contact.

Protoplast transformation of glutamate-producing bacteria with plasmid DNA

A method for polyethylene glycol-induced protoplast transformation of glutamate-producing bacteria with plasmid DNA was established. Protoplasts were prepared from cells grown in the presence of penicillin by treatment with lysozyme in a hypertonic medium. The concentration of penicillin during growth affected the efficiency of formation, regeneration, and polyethylene glycol-induced DNA uptake of protoplasts. Regeneration of protoplasts was accomplished on a hypertonic agar medium containing sodium succinate and yeast extract. The spectinomycin and streptomycin resistance plasmid pCG4, originally from Corynebacterium glutamicum T250, could transform various glutamate-producing bacteria such as C. glutamicum, Corynebacterium herculis, Brevibacterium flavum, and Microbacterium ammoniaphilum. The plasmid was structurally unchanged and stably maintained in new hosts. The transformation frequency of most competent protoplasts with pCG4 DNA isolated from primary transformants was high (ca. 10(6) transformants per microgram of covalently closed circular DNA) but was still two orders of magnitude below the frequency of transfection with modified DNA of the bacteriophage phi CGI. The difference was ascribed to the involvement of regeneration in transformation.

Genetic transformation of Bacillus brevis 47, a protein-secreting bacterium, by plasmid DNA

A method has been developed for introducing plasmid DNA into Bacillus brevis 47, a protein-secreting bacterium. Treatment of B. brevis 47 cells with 50 mM Tris-hydrochloride buffer of alkaline pH was effective for inducing DNA uptake competence. In the presence of polyethylene glycol, the Tris-treated cells incorporated plasmid DNA with a frequency of 10(-4) (transformants per viable cell) when 1 microgram of plasmid DNA was added to 10(9) Tris-treated cells. The pH of Tris-hydrochloride buffer as well as the concentration and molecular weight of the polyethylene glycol affected the transformation frequency. The growth phase of B. brevis 47 cells strongly influenced the frequency. Two plasmids, pHW1 and pUB110, have been introduced into B. brevis 47 by this method. The mechanism of induction of competence for DNA uptake in connection with removal of the outer two protein layers of the cell wall by treatment of B. brevis 47 cells with Tris-hydrochloride buffer is discussed.

Construction and characterization of plasmid vectors for cloning in Staphylococcus aureus and Staphylococcus carnosus

Several plasmid vectors for cloning in Staphylococcus aureus and S. carnosus have been constructed and characterized. The chimeric plasmids are composed of parts of the following parental plasmids: The chloramphenicol-resistance plasmid, pC194, the tetracycline-resistance plasmid, pMK148, and the erythromycin-resistance plasmid, pE12. All the chimeric plasmids confer two selectable antibiotic-resistance markers on host cells. Insertional inactivation of the various antibiotic-resistance markers occurred at the BclI site of pE12, and the Sau96- or AvaII-site of pMK148; only a slight inactivation of the chloramphenicol-resistance marker occurred at the HaeIII-site of pC194. The chimeric plasmids pCT20 and pCE10 are both stable in S. aureus and S. carnosus. In addition, the hybrid plasmids of pCT20 and pCE10, containing lambda-DNA fragments in various restriction sites between 0.4 and 1.2 kb, are stably maintained. The inserted lambda-DNA fragments appear unchanged.

Polyethylene glycol-dependent transfection of Acholeplasma laidlawii with mycoplasma virus L2 DNA

Phenol-extracted DNA from mycoplasma virus L2 was able to transfect Acholeplasma laidlawii in the presence of polyethylene glycol. Transfection was sensitive to DNase and was most efficient with 36% (wt/vol) polyethylene glycol 8000 and cells in logarithmic growth. Virus production by the transfected cells was similar to that of the cells infected by intact virus. L2 DNA transfected A. laidlawii with a single-hit dose-response curve, reaching saturation at high DNA concentrations. Optimum transfection frequencies were about 10(-7) transfectants per L2 DNA molecule and 10(-4) transfectants per CFU. When DNA was present in saturating amounts, the number of transfectants increased linearly with the number of CFU present in the transfection mixture, suggesting that DNA uptake does not occur by a mechanism involving cell fusion. The cleavage of the superhelical mycoplasma virus L2 genome with restriction endonucleases that cleave the DNA molecule once reduced the transfection frequency. Host cell modification and restriction of transfecting L2 DNA were similar to those for infecting L2 virions.

Megacinogenic plasmids of Bacillus megaterium

Megacins A-216 and A-19213 in Bacillus megaterium are plasmid encoded, as shown by analysis of cured, non-megacinogenic (Meg-) derivatives of strains 216 and ATCC 19213 and by polyethylene glycol-mediated protoplast transformation of Meg- bacteria with plasmid DNA. The results of both techniques implicated a 31-megadalton plasmid, pBM309, in megacin A-216 production and a 29-megadalton plasmid, pBM113, in megacin A-19213 production.

Chloramphenicol acetyltransferase: enzymology and molecular biology

Naturally occurring chloramphenicol resistance in bacteria is normally due to the presence of the antibiotic inactivating enzyme chloramphenicol acetyltransferase (CAT) which catalyzes the acetyl-S-CoA-dependent acetylation of chloramphenicol at the 3-hydroxyl group. The product 3-acetoxy chloramphenicol does not bind to bacterial ribosomes and is not an inhibitor of peptidyltransferase. The synthesis of CAT is constitutive in E. coli and other Gram-negative bacteria which harbor plasmids bearing the structural gene for the enzyme, whereas Gram-positive bacteria such as staphylococci and streptococci synthesize CAT only in the presence of chloramphenicol and related compounds, especially those with the same stereochemistry of the parent compound and which lack antibiotic activity and a site of acetylation (3-deoxychloramphenicol). Studies of the primary structures of CAT variants suggest a marked degree of heterogeneity but conservation of amino acid sequence at and near the putative active site. All CAT variants are tetramers composed in each case of identical polypeptide subunits consisting of approximately 220 amino acids. The catalytic mechanism does not appear to involve an acyl-enzyme intermediate although one or more cysteine residues are protected from thiol reeagents by substrates. A highly reactive histidine residue has been implicated in the catalytic mechanism.

Transformation of Streptococcus lactis Protoplasts by Plasmid DNA

Polyethylene glycol-treated protoplasts prepared from Streptococcus lactis LM3302, a lactose-negative (Lac − ) derivative of S. lactis ML3, were transformed to lactose-fermenting ability by a transductionally shortened plasmid (pLM2103) coding for lactose utilization.

Transformation of Bacillus stearothermophilus with plasmid DNA and characterization of shuttle vector plasmids between Bacillus stearothermophilus and Bacillus subtilis

A thermophilic bacterium Bacillus stearothermophilus IFO 12550 (ATCC 12980) was transformed with each of the following plasmids, pUB110 (kanamycin resistance, Kmr), pTB19 (Kmr and tetracycline resistance [Tcr]), and its derivative pTB90 (Kmr Tcr), by the protoplast procedure in the presence of polyethylene glycol at 48 degrees C. The transformation frequencies per regenerant for pUB110, pTB19, and pTB90 were 5.9 x 10(-3), 5.5 x 10(-3), and 2.0 x 10(-1), respectively. Among these plasmids, pTB90 was newly derived, and the restriction endonuclease cleavage map was constructed. When tetracycline (5 micrograms/ml) was added into the culture medium, the copy number of pTB90 in B. stearothermophilus was about fourfold higher than that when kanamycin (5 micrograms/ml) was added instead of tetracycline. Bacillus subtilis could also be transformed with the plasmids extracted from B. stearothermophilus and vice versa. Accordingly, pUB110, pTB19, and pTB90 served as shuttle vectors between B. stearothermophilus and B. subtilis. The requirements for replication of pTB19 in B. subtilis and B. stearothermophilus appear to be different, because some deletion plasmids (pTB51, pTB52, and pTB53) derived from pTB19 could replicate only in B. subtilis, whereas another deletion plasmid pTB92 could replicate solely in B. stearothermophilus. Plasmids pTB19 and pTB90 could be maintained and expressed in B. stearothermophilus up to 65 degrees C, whereas the expression of pUB110 in the same strain was up to 55 degrees C.

Plasmid-chromosomal transition of genes important in staphylococcal enterotoxin B expression

Experiments were performed to further elucidate the genetic mechanisms underlying the synthesis of staphylococcal enterotoxin B (SEB). Our laboratory has previously shown that, in strains of Staphylococcus aureus which harbor a 1.15-megadalton plasmid (pentB or pSN2), the plasmid appears to be required for SEB synthesis; in other S. aureus strains, designated chromosomal SEB producers, this 1.15-megadalton plasmid is conspicuously absent. We report here than in both Bacillus subtilis minicells and a coupled translational assay, pSN2 codes for a polypeptide of 18,000 daltons. This product is not immunologically reactive with purified anti-SEB globulin. Nevertheless, pSN2 is necessary but not sufficient for SEB synthesis in strains which harbor the plasmid. Further, the data provide a reasonable link between plasmid-bearing and chromosomal SEB producers: transformational analysis indicates that both require functions specified (in plasmid-bearing strains) by pSN2 for SEB synthesis. The combined genetic and biochemical data suggest that pSN2 is not the reservoir for the SEB structural gene, but that the pSN2-specific functions required for SEB synthesis are regulatory in nature.