Insecticidal Bacillus thuringiensis silences Erwinia carotovora virulence by a new form of microbial antagonism, signal interference

It is commonly known that bacteria may produce antibiotics to interfere with the normal biological functions of their competitors in order to gain competitive advantages. Here we report that Bacillus thuringiensis suppressed the quorum-sensing-dependent virulence of plant pathogen Erwinia carotovora through a new form of microbial antagonism, signal interference. E. carotovora produces and responds to acyl-homoserine lactone (AHL) quorum-sensing signals to regulate antibiotic production and expression of virulence genes, whereas B. thuringiensis strains possess AHL-lactonase, which is a potent AHL-degrading enzyme. B. thuringiensis did not seem to interfere with the normal growth of E. carotovora; rather, it abolished the accumulation of AHL signal when they were cocultured. In planta, B. thuringiensis significantly decreased the incidence of E. carotovora infection and symptom development of potato soft rot caused by the pathogen. The biocontrol efficiency is correlated with the ability of bacterial strains to produce AHL-lactonase. While all the seven AHL-lactonase-producing B. thuringiensis strains provided significant protection against E. carotovora infection, Bacillus fusiformis and Escherichia coli strains that do not process AHL-degradation enzyme showed little effect in biocontrol. Mutation of aiiA, the gene encoding AHL-lactonase in B. thuringiensis, resulted in a substantial decrease in biocontrol efficacy. These results suggest that signal interference mechanisms existing in natural ecosystems could be explored as a new version of antagonism for prevention of bacterial infections.

Colloidal chitin stained with Remazol Brilliant Blue R, a useful substrate to select chitinolytic microorganisms and to evaluate chitinases

A simple and sensitive method based on the use of colloidal chitin stained with Remazol Brilliant Blue R (RBB) is proposed to evaluate chitinase activity. If this colloidal-stained substrate is included as a carbon source in a liquid medium, this technique allows the selection or the comparison of chitinolytic microorganisms. The colloidal substrate is proportionally solubilized and the dye released is spectrophotometrically quantified at 595 nm. The procedures used for the staining and fixing of RBB in the colloidal chitin, and a comparison with the commercial substrate chitin-azure, are presented. The influence of several physicochemical and enzymatic parameters on the release of dyes is also shown. Both stained substrates were used for studying the effect of pH, substrate concentration, temperature and time on the chitinase reaction of Bacillus thuringiensis Bt-107.

Improving the insecticidal activity of Bacillus thuringiensis subsp. aizawai against Spodoptera exigua by chromosomal expression of a chitinase gene

A transcriptionally fused gene comprising the P19 gene from Bacillus thuringiensis subsp. israelensis fused with a chitinase gene (chiBlA) from B. licheniformis was integrated into the B. thuringiensis subsp. aizawai BTA1 genome by homologous recombination. The resulting B. thuringiensis subsp. aizawai strain (INT1) showed growth and sporulation comparable with that of the wild-type strain. INT1 produced four chitinases of different molecular masses (i.e., 66, 55, 39, 36 kDa). Three of these (66, 55, 36 kDa) were derived from the cloned chiBlA gene, whereas the 39-kDa chitinase originated from BTA1. Using surface contamination bioassays, the 50% lethal concentration of lyophilized whole culture broth of INT1 against Spodoptera exigua neonate larvae was 12.2 microg/cm2, compared with 30.8 microg/cm2 for BTA1. Bioassays using filtered culture supernatant of INT1 (110 microg/cm2) together with trypsin-activated purified Cry1C protein of B. thuringiensis (1,280 ng/cm2) showed 75.0% mortality, compared with 56.7% mortality for Cry1C combined with BTA1 at the same concentration. Using scanning electron microscopy, clear perforations were observed in S. exigua fifth instar peritrophic membranes incubated with either crude or purified chitinase, or isolated from fifth instar S. exigua fed purified chitinase since the first instar. These results show that chitinase can increase the activity of B. thuringiensis subsp. aizawai against S. exigua. This is the first documentation of expressing a chimeric chitinase gene on the chromosome of B. thuringiensis; and chromosomal integration might be used as a potential technique for strain improvement.

Molecular cloning and sequence analysis of the chitinase gene from Bacillus thuringiensis serovar alesti

Endogenous chitinase plays a positive role in the pathogenicity of Bacillus thuringiensis to insect pests. The chitinase gene was cloned from B. thuringiensis serovar alesti strain HD-16, and the deduced 676 amino acid sequence showed a high degree of similarity with other Bacillus chitinases. Additionally, the deduced amino acid sequence showed that the protein contained an amino terminus signal peptide and consisted of a catalytic domain, a fibronectin type III domain and a chitin-binding domain. All three domains showed conserved sequences when compared to other bacterial chitinase or cellulase sequences.

A facile analytical method for the identification of protease gene profiles from Bacillus thuringiensis strains

Five pairs of degenerate universal primers have been designed to identify the general protease gene profiles from some distinct Bacillus thuringiensis strains. Based on the PCR amplification patterns and DNA sequences of the cloned fragments, it was noted that the protease gene profiles of the three distinct strains of B. thuringiensis subsp. kurstaki HD73, tenebrionis and israelensis T14001 are varied. Seven protease genes, neutral protease B (nprB), intracellular serine protease A (ispA), extracellular serine protease (vpr), envelope-associated protease (prtH), neutral protease F (nprF), thermostable alkaline serine protease and alkaline serine protease (aprS), with known functions were identified from three distinct B. thuringiensis strains. In addition, five DNA sequences with unknown functions were also identified by this facile analytical method. However, based on the alignment of the derived protein sequences with the protein domain database, it suggested that at least one of these unknown genes, yunA, might be highly protease-related. Thus, the proposed PCR-mediated amplification design could be a facile method for identifying the protease gene profiles as well as for detecting novel protease genes of the B. thuringiensis strains.

The IspA protease's involvement in the regulation of the sporulation process of Bacillus thuringiensis is revealed by proteomic analysis

We have observed that the process of sporulation of the ispA-deficient mutant was delayed under phase-contrast microscopy. The protein profiles of the ispA-deficient mutant have been analyzed using two-dimensional gel electrophoresis. The results of a proteomic analysis using MALDI-TOF MS indicated that a sporulation-associated protein, pro- [Formula: see text], was upregulated, while two other sporulation-associated proteins, SpoVD and SpoVR, were downregulated in the ispA-deficient mutant. It has been known that pro- [Formula: see text] is a precursor of [Formula: see text] and is required for gene expression related to the late stage of sporulation. Moreover, SpoVD and SpoVR are known to be involved in the formation of the spore cortex. Based on these observations, we propose that the delay in the sporulation process observed in the ispA-deficient mutant may be due to a failure of [Formula: see text] to signal sporulation. This phenomenon may be further enhanced by insufficient amount of SpoVD and SpoVR for cortex formation. In this study, we have revealed for the first time a possible pathway for the regulation of sporulation-associated proteins via IspA.

Beta-glucosidase enzymatic activity of crystal polypeptide of the Bacillus thuringiensis strain 1.1

The crystals of Bacillus thuringiensis strain 1.1 consist of the 140 kDa delta-endotoxin, which exhibits beta-glucosidase enzymatic activity, based on the following data. (i) Purified crystals exhibit beta-glucosidase enzymatic activity. When the crystals are reacted with specific antibodies directed either against the commercial (almond purified) beta-glucosidase or against the 140 kDa polypeptide, then considerable reduction of enzymatic activity is observed almost at the same level with both antibodies. (ii) Commercial beta-glucosidase and the 140 kDa crystal polypeptide share antigenic similarities; in Western immunoblots, the 140 kDa crystal polypeptide is recognized by anti-beta-glucosidase antibodies, and commercial beta-glucosidase is recognized by anti-140-kDa antibodies. (iii) The enzymatic properties of commercial beta-glucosidase and that resident in the crystals of B. thuringiensis strain 1.1 are very similar. Thus, both enzymes hydrolyze a wide range of substrates (aryl-beta-glucosides, disaccharides with alpha- or beta-linkage polysaccharides) and have an optimum activity at 40 degrees C and pH 5. Both enzymes are relatively thermostable and are resistant to end-product inhibition by glucose. Additionally, they show the same pattern of inhibition or activation by several chemical compounds. (iv) The crystals and commercial beta-glucosidase show almost equivalent levels of insecticidal activity against Drosophila melanogaster larvae and, furthermore, cause reduction in adult flies that emerge from larvae surviving treatment.

Chitosanase activity in Bacillus thuringiensis

The ability to produce extracellular chitosanase (EC 3.2.1.132) was found by plate assays in 18 (23%) out of 77 crystalliferous strains of Bacillus thuringiensis. The best chitosanase producer was selected after the growth chosen in a liquid medium with colloidal chitosan as carbon source. Enzyme production was optimized (a 4-d incubation at 32 degrees C with shaking in a medium of pH 6.5 with 4% colloidal chitosan) and the enzyme was partially characterized. This is the first report on the chitosanase of B. thuringiensis.

A constitutively expressed 36 kDa exochitinase from Bacillus thuringiensis HD-1

A 36 kDa chitinase was purified by ion exchange and gel filtration chromatography from the culture supernatant of Bacillus thuringiensis HD-1. The chitinase production was independent of the presence of chitin in the growth medium and was produced even in the presence of glucose. The purified chitinase was active at acidic pH, had an optimal activity at pH 6.5, and showed maximum activity at 65 degrees C. Of the various substrates, the enzyme catalyzed the hydrolysis of the disaccharide 4-MU(GlnAc)(2) most efficiently and was therefore classified as an exochitinase. The sequence of the tryptic peptides showed extensive homology with Bacillus cereus 36 kDa exochitinase. The 1083 bp open reading frame encoding 36 kDa chitinase was amplified with primers based on the gene sequence of B. cereus 36 kDa exochitinase. The deduced amino-acid sequence showed that the protein contained an N-terminal signal peptide and consisted of a single catalytic domain. The two conserved signature sequences characteristic of family 18 chitinases were mapped at positions 105-109 and 138-145 of Chi36. The recombinant chitinase was expressed in a catalytically active form in Escherichia coli in the vector pQE-32. The expressed 36 kDa chitinase potentiated the insecticidal effect of the vegetative insecticidal protein (Vip) when used against neonate larvae of Spodoptera litura.

Identification of a Novel DNA Methyltransferase Activity from Bacillus thuringiensis

A DNA methyltransferase activity was identified in a strain of Bacillus thuringiensis that was found to protect DNA from cleavage by the restriction endonuclease HaeIII at overlapping sites. Site-directed mutagenesis was used to confirm therecognition sequence of the methyltransferase as ACGGC.

Optimizing the interfacial binding and activity of a bacterial phosphatidylinositol-specific phospholipase C

The phosphatidylinositol-specific phospholipase C from Bacillus thuringiensis can be activated by nonsubstrate interfaces such as phosphatidylcholine micelles or bilayers. This activation corresponds with partial insertion into the interface of two tryptophans, Trp-47 in helix B and Trp-242 in a loop, in the rim of the alphabeta-barrel. Both W47A and W242A have much weaker binding to interfaces and considerably lower kinetic interfacial activation. Tryptophan rescue mutagenesis, reinsertion of a tryptophan at a different place in helix B in the W47A mutant or in the loop (residues 232-244) of the W242A mutant, has been used to determine the importance and orientation of a tryptophan in these two structural features. Phosphotransferase and phosphodiesterase assays, and binding to phosphatidylcholine vesicles were used to assess both orientation and position of tryptophans needed for interfacial activity. Of the helix B double mutants, only one mutant, I43W/W47A, has tryptophan in the same orientation as Trp-47. I43W/W47A shows recovery of phosphatidylinositol-specific phospholipase C (PC) activation of d-myo-inositol 1,2-cyclic phosphate hydrolysis. However, the specific activity toward phosphatidylinositol is still lower than wild type enzyme and high activity with phosphatidylinositol solubilized in 30% isopropyl alcohol (a hallmark of the native enzyme) is lost. Reinserting a tryptophan at several positions in the loop composed of residues 232-244 partially recovers PC activation and affinity of the enzyme for lipid interfaces as well as activation by isopropyl alcohol. G238W/W242A shows an enhanced activation and affinity for PC interfaces above that of wild type. These results provide constraints on how this bacterial phosphatidylinositol-specific phospholipase C binds to activating PC interfaces.

Water-miscible organic cosolvents enhance phosphatidylinositol-specific phospholipase C phosphotransferase as well as phosphodiesterase activity

Phosphatidylinositol-specific phospholipase C (PI-PLC) from Bacillus thuringiensis catalyzes the hydrolysis of phosphatidylinositol (PI) in a Ca(2+)-independent two-step mechanism: (i) an intramolecular phosphotransferase reaction to form inositol 1,2-(cyclic)-phosphate (cIP), followed by (ii) a cyclic phosphodiesterase activity that converts cIP to inositol 1-phosphate (I-1-P). Moderate amounts of water-miscible organic solvents have previously been shown to dramatically enhance the cyclic phosphodiesterase activity, that is, hydrolysis of cIP. Cosolvents [isopropanol (iPrOH), dimethylsufoxide (DMSO), and dimethylformamide (DMF)] also enhance the phosphotransferase activity of PI-PLC toward PI initially presented in vesicles, monomers, or micelles. Although these water-miscible organic cosolvents caused large changes in PI particle size and distribution (monitored with pyrene-labeled PI fluorescence, 31P NMR spectroscopy, gel filtration, and electron microscopy) that differed with the activating solvent, the change in PI substrate structure in different cosolvents was not correlated with the enhanced catalytic efficiency of PI-PLC toward its substrates. PI-PLC stability was decreased in water/organic cosolvent mixtures (e.g., the T(m) for PI-PLC thermal denaturation decreased linearly with added iPrOH). However, the addition of myo-inositol, a water-soluble inhibitor of PI-PLC, helped stabilize the protein. At 30% iPrOH and 4 degrees C (well below the T(m) for PI-PLC in the presence of iPrOH), cosolvent-induced changes in protein secondary structure were minimal. iPrOH and diheptanoylphosphatidylcholine, each of which activates PI-PLC for cIP hydrolysis, exhibited a synergistic effect for cIP hydrolysis that was not observed with PI as substrate. This behavior is consistent with a mechanism for cosolvent activation that involves changes in active site polarity along with small conformational changes involving the barrel rim tryptophan side chains that have little effect on protein secondary structure.

[Cloning and sequencing of chitinase gene from Bacillus thuringiensis subsp israelensis]

Chitin, a linear homopolymer of N-acetyl-D-glucosamine, is a common constituent of fungal cell walls, exoskeletons of insects, and shells of invertebrates. Thus, chitinase, a chitin hydrolytic enzyme, has become of interest for potential use as biopesticides for controlling insect pests. Using a pair of specific primers, chitinase gene (ichi) was amplified by touchdown PCR from Bacillus thuringiensis subsp israelensis chromosomal DNA, and then subcloned into pGEM-T easy vector. ichi sequence (GenBank Accession Number: AF526379) with a length of 2570 bp included an open reading frame (ORF) of 2067 bp, which contained 688 amino acids with Mr = 75.79 kDa and pI = 5.90. The amino acid sequence of ichi gene shows 97.24%, 97.18%, 97.63% and 63.07% identity to that of Bacillus cereus strain 28-9 chitinase CW, Bacillus cereus CH chitinase B, Bt subsp Mexican chitinase, and Bt subsp pakistani chitinase A71, respectively. It was demonstrated that Ichi contains a signal peptide (46 amino acid residues) and three functional domains: an N-terminal catalytic domain (105 amino acid residues), a fibronectin type III like domain (74 amino acid residues), and a C-terminal chitin-binding domain (40 amino acid residues).

Cloning, sequencing, and expression of the chitinase gene chiA74 from Bacillus thuringiensis

The endochitinase gene chiA74 from Bacillus thuringiensis serovar kenyae strain LBIT-82 was cloned in Escherichia coli DH5 alpha F'. A sequence of 676 amino acids was deduced when the gene was completely sequenced. A molecular mass of 74 kDa was estimated for the preprotein, which includes a putative 4-kDa signal sequence located at the N terminus. The deduced amino acid sequence showed high degree of identity with other chitinases such as ChiB from Bacillus cereus (98%) and ChiA71 from Bacillus thuringiensis serovar pakistani (70%). Additionally, ChiA74 showed a modular structure comprised of three domains: a catalytic domain, a fibronectin-like domain, and a chitin-binding domain. All three domains showed conserved sequences when compared to other bacterial chitinase sequences. A ca. 70-kDa mature protein expressed by the cloned gene was detected in zymograms, comigrating with a chitinase produced by the LBIT-82 wild-type strain. ChiA74 is active within a wide pH range (4 to 9), although a bimodal activity was shown at pH 4.79 and 6.34. The optimal temperature was estimated at 57.2 degrees C when tested at pH 6. The potential use of ChiA74 as a synergistic agent, along with the B. thuringiensis insecticidal Cry proteins, is discussed.

Intracellular proteases of Bacillus thuringiensis subsp. kurstaki and a protease-deficient mutant Btk-q

The commencement of intracellular protease synthesis was studied by gelatin zymography in Bacillus thuringiensis ( Btk) HD1, Btk HD73, and a protease-deficient mutant Btk-q derived from the former strain. By gelatin zymography, a 92-kDa protease was detected first at 3 h of sporulation, which continued until 48 h, whereas two other proteases of mol wt 78 and 69 kDa were detectable from 6 h onwards and continued until 48 h of growth in Btk HD1. Similar studies revealed the presence of two major intracellular proteases in Btk HD73 by gelatin zymography, which first appeared at 6 h of sporulation and continued until 48 h of growth. The quantitative azocasein assay confirmed that the total protease activity increases from 3 to 21 h, thereafter reaching a plateau up to 48 h of growth examined, in HD1 and HD73 strains. Btk-q, a protease-deficient mutant, showed traces of protease activity by azocasein analysis that could not be detected by gelatin zymography. The free amino acid pool content was also increased parallel to the way that the protease activity increased in all three strains. However, this increase was found to be low (16-fold) in Btk-q when compared with Btk HD1 and HD73 strains. The following amino acids were detected by paper chromatography in Btk HD1: DL-alanine, L-glutamic acid, L-aspartic acid, tyrosine, tryptophan/methionine/valine, arginine, leucine/norleucine/isoleucine, and glycine, whereas only DL-alanine, L-glutamic acid, and L-aspartic acid were in Btk-q at 24 and 48 h, when the protease activity was maximum.

Chitinolytic activities in Bacillus thuringiensis and their synergistic effects on larvicidal activity

AIMS

To investigate the distribution of chitinase in Bacillus thuringiensis strains, and the enhancing effects of the chitinase-producing B. thuringiensis strains on insecticidal toxicity of active B. thuringiensis strain against Spodoptera exigua larvae.

METHODS AND RESULTS

The chitinolytic activities of B.thuringiensis strains representing the 70 serotypes were investigated by the whitish opaque halo and the colorimetric method. Thirty-eight strains produced different levels of chitinase at pH 7.0, and so did 17 strains at pH 10.0. The strain T04A001 exhibited the highest production, reaching a specific activity of 355 U ml(-1) in liquid medium. SDS-PAGE and Western blotting showed that the chitinase produced by some B. thuringiensis strains had a molecular weight of about 61 kDa. The bioassay results indicated that the chitinase-producing B. thuringiensis strains could enhance the insecticidal activity of B. thuringiensis strain DL5789 against S. exigua larvae, with an enhancing ratio of 2.35-fold.

CONCLUSION

This study demonstrated that chitinase was widely produced in B. thuringiensis strains and some of the strains could enhance the toxicity of active B. thuringiensis strain.

SIGNIFICANCE AND IMPACT OF THE STUDY

This is the first investigation devoted exclusively to analyse the distribution of chitinase in B. thuringiensis. It infers that the chitinase produced by B. thuringiensis might play a role in the activity of the biopesticide.

Contribution of membrane-damaging toxins to Bacillus endophthalmitis pathogenesis

Membrane-damaging toxins are thought to be responsible for the explosive clinical course of Bacillus endophthalmitis. This study analyzed the contribution of phosphatidylinositol-specific phospholipase C (PI-PLC) and phosphatidylcholine-specific phospholipase C (PC-PLC) to the pathogenesis of experimental Bacillus endophthalmitis. Isogenic mutants were constructed by insertion of lacZ into Bacillus thuringiensis genes encoding PI-PLC (plcA) and PC-PLC (plcB). Rabbit eyes were injected intravitreally with 2 log(10) CFU of strain BT407 (wild type), the PI-PLC mutant (BTplcA::lacZ), or the PC-PLC mutant (BTplcB::lacZ). The rates of decrease in retinal responses of eyes infected with the isogenic mutants were similar to that of wild type, with all infections resulting in elimination of retinal function by 18 h. Strain BT407 caused a significant increase in the latency of retinal responses at 6 h, but strains BTplcA::lacZ and BTplcB::lacZ did not. All strains elicited significant inflammatory cell influx into the anterior chamber by 12 h. Histologically, eyes infected with each strain were indistinguishable throughout the infection course. In this model, neither PI-PLC nor PC-PLC had an effect on the course or severity of experimental Bacillus endophthalmitis. Alterations in retinal responses early in infection may mark the beginnings of specific photoreceptor or glial cell dysfunction.

Genes encoding the N-acyl homoserine lactone-degrading enzyme are widespread in many subspecies of Bacillus thuringiensis

Gram-negative bacteria can communicate with each other by N-acyl homoserine lactones (AHLs), which are quorum-sensing autoinducers. Recently, the aiiA gene (encoding an enzyme catalyzing the degradation of AHL) has been cloned from Bacillus sp. strain 240B1. During investigations in the course of the ongoing Bacillus thuringiensis subsp. morrisoni genome project, an aiiA homologue gene in the genome sequence was found. These results led to consideration of the possibility of the widespread existence of the gene in B. thuringiensis. aiiA homologue genes were found in 16 subspecies of B. thuringiensis, and their sequences were determined. Comparison of the Bacillus sp. strain 240B1 aiiA gene with the B. thuringiensis aiiA homologue genes showed high homologies of 89 to 95% and 90 to 96% in the nucleotide sequence and deduced amino acid sequence, respectively. Among the subspecies of B. thuringiensis having an aiiA gene, the subspecies aizawai, galleriae, kurstaki, kyushuensis, ostriniae, and subtoxicus were shown to degrade AHL. It was observed that recombinant Escherichia coli producing AiiA proteins also had AHL-degrading activity and could also attenuate the plant pathogenicity of Erwinia carotovora. These results indicate that insecticidal B. thuringiensis strains might have potential to compete with gram-negative bacteria in natural ecosystems by autoinducer-degrading activity.

The InhA2 metalloprotease of Bacillus thuringiensis strain 407 is required for pathogenicity in insects infected via the oral route

The entomopathogenic bacterium Bacillus thuringiensis is known to secrete a zinc metalloprotease (InhA) that specifically cleaves antibacterial peptides produced by insect hosts. We identified a second copy of the inhA gene, named inhA2, in B. thuringiensis strain 407 Cry(-). The inhA2 gene encodes a putative polypeptide showing 66.2% overall identity with the InhA protein and harboring the zinc-binding domain (HEXXH), which is characteristic of the zinc-requiring metalloproteases. We used a transcriptional inhA2'-lacZ fusion to show that inhA2 expression is induced at the onset of the stationary phase and is overexpressed in a Spo0A minus background. The presence of a reverse Spo0A box in the promoter region of inhA2 suggests that Spo0A directly regulates the transcription of inhA2. To determine the role of the InhA and InhA2 metalloproteases in pathogenesis, we used allelic exchange to isolate single and double mutant strains for the two genes. Spores and vegetative cells of the mutant strains were as virulent as those of the parental strain in immunized Bombyx mori larvae infected by the intrahemocoelic route. Exponential phase cells of all the strains displayed the same in vitro potential for colonizing the vaccinated hemocoel. We investigated the synergistic effect of the mutant strain spores on the toxicity of Cry1C proteins against Galleria mellonella larvae infected via the oral pathway. The spores of DeltainhA2 mutant strain were ineffective in providing synergism whereas those of the DeltainhA mutant strain were not. These results indicate that the B. thuringiensis InhA2 zinc metalloprotease has a vital role in virulence when the host is infected via the oral route.

[Entomopathogenic bacteria Bacillus thuringiensis as producers of restriction endonucleases]

A total of 115 collection strains of Bacillus thuringiensis, belonging to various subspecies, have been studied for the presence of DNA restriction-modification systems. Restriction endonucleases of 13 strains have been isolated and characterized. No considerable correlations between the taxonomic positions of the bacteria and the specificities of the endonucleases isolated have been detected. It is concluded that the enzymes with identical specificities are present in both the crystalliferous and acrystalliferous strains of the same subspecies.

Simultaneous production of biopesticide and alkaline proteases by Bacillus thuringiensis using sewage sludge as a raw material

The simultaneous production of Bacillus thuringiensis (Bt) based biopesticide and proteases was studied using synthetic medium and wastewater sludge as a raw material. The studies were conducted in shake flask and computer controlled 15-L capacity fermentors. Measuring viable cell and spore counts, entomotoxicity and protease activity monitored the progress of the biopesticide production process. A higher viable cell count and spore count was observed in synthetic Soya medium, however, higher entomotoxicity and protease activity were observed in wastewater sludge medium. Thus, the wastewater sludge is a better raw material than commercial Soya medium for the biopesticides and enzyme production. The maximum entomotoxicity and protease activity observed in the fermentor was 9,332 IU/microL and 4.58 IU/mL, respectively. The proteases produced by Bt were also characterised. Two types of proteases were detected; neutral proteases with pH optimum 7.0 and alkaline proteases with pH optimum 10-11. Further, two types of alkaline proteases were detected; one having a pH and temperature optimum at 10 and 50 degrees C while the other at 11 and 70 degrees C. The protease thermal stability was found to increase in the presence of CaCl2, indicating the proteases were metalloproteases.

Deletion of aprA and nprA genes for alkaline protease A and neutral protease A from bacillus thuringiensis: effect on insecticidal crystal proteins

The aprA gene encoding alkaline protease A (AprA) was cloned from Bacillus thuringiensis subsp. kurstaki, and the cloned gene was used to construct aprA-deleted (aprA1) strains of B. thuringiensis. An aprA1 strain of B. thuringiensis that contained the wild-type gene for neutral protease A (nprA(+)) displayed levels of extracellular proteolytic activity that were similar to those of an aprA(+)nprA(+) strain. However, when EDTA was included in the protease assay to inhibit NprA activity the aprA1nprA(+) strain displayed only 2% of the extracellular proteolytic activity of the aprA(+)nprA(+) strain. A strain that was deleted for both aprA and nprA (aprA1nprA3 strain) failed to produce detectable levels of proteolytic activity either in the presence or absence of EDTA in the assay. Compared with the aprA(+)nprA(+) strain the aprA1nprA(+) strain yielded 10% more full-length Cry1Bb crystal protein and the aprA1nprA3 strain yielded 25% more full-length Cry1Bb protein. No significant differences were seen in the 50% lethal dose of Cry1Bb protein from aprA(+)nprA(+) and aprA1nprA3 strains against three species of lepidopteran insects. These results suggest that enhanced yield of certain crystal proteins can be obtained by deletion of the genes aprA and nprA which are the major extracellular proteases of B. thuringiensis.

Chitinase from Bacillus thuringiensis subsp. pakistani

The chitinase gene (chiA71) from Bacillus thuringiensis subsp. pakistani consists of an open reading frame of 1,905 nucleotides encoding 635 amino acid residues with an estimated molecular mass of 71 kDa. Comparison of the deduced amino acid sequence of the mature enzyme to other microbial chitinases shows a putative catalytic domain and a region with conserved amino acids similar to that of the type III module of fibronectin and a chitin-binding domain. By activity detection of chitinase on SDS-PAGE after renaturation, the molecular mass of protein bands with chitinase activity were 66, 60, 47, and 32 kDa. The N-terminal amino acid sequence of each chitinase activity band was the same (Asp-Ser-Pro-Lys-Gln), suggesting that the 60-, 47-, and 32-kDa chitinases were derived from the 66-kDa chitinase by processing step(s) at the C-terminus. The enzyme was identified as an exochitinase, since it generated N-acetylglucosamine from early stage of colloidal chitin hydrolysis. The crude protein (2.3-18.4 mg/ml), containing chitinase at final activities of 8, 16, 32, and 64 mU/ml, was toxic to Aedes aegypti larvae and caused mortalities of 7.5, 15.0, 51.3, and 70.0% respectively, but the same amount of crude protein from a B. thuringiensis subsp. pakistani mutant lacking chitinase was not toxic.

Comparison of the omega-transaminases from different microorganisms and application to production of chiral amines

Microorganisms that are capable of (S)-enantioselective transamination of chiral amines were isolated from soil samples by selective enrichment using (S)-alpha-methyl-benzylamine ((S)-alpha-MBA) as a sole nitrogen source. Among them, Klebsiella pneumoniae JS2F, Bacillus thuringiensis JS64, and Vibrio fluvialis JS17 showed good omega-transaminase (omega-TA) activities and the properties of the omega-TAs were investigated. The induction level of the enzyme was strongly dependent on the nitrogen source for the strains, except for V. fluvialis JS17. All the omega-TAs showed high enantioselectivity (E>50) toward (S)-alpha-MBA and broad amino donor specificities for arylic and aliphatic chiral amines. Besides pyruvate, aldehydes such as propionaldehyde and butyraldehyde showed good amino acceptor reactivities. All the omega-TAs showed substrate inhibition by (S)-alpha-MBA above 200 mm. Moreover, substrate inhibition by pyruvate above 10 mm was observed for omega-TA from V. fluvialis JS17. In the case of product inhibition, acetophenone showed much greater inhibitions than L-alanine for all omega-TAs. Comparison of the enzyme properties indicates that omega-transaminase from V. fluvialis JS17 is the best one for both kinetic resolution and asymmetric synthesis to produce enantiomerically pure chiral amines. Kinetic resolution of sec-butylamine (20 mM) was done under reduced pressure (150 Torr) to selectively remove an inhibitory product (2-butanone) using the enzyme from V. fluvialis JS17. Enantiomeric excess of (R)-sec-butylamine reached 94.7% after 12 h of reaction.

Identification of genes involved in the activation of the Bacillus thuringiensis inhA metalloprotease gene at the onset of sporulation

The immune inhibitor A (InhA) metalloprotease from Bacillus thuringiensis specifically cleaves antibacterial proteins produced by the insect host, suggesting that it may contribute to the overall virulence of B. thuringiensis. The transcriptional regulation of the inhA gene in both B. thuringiensis and Bacillus subtilis was investigated. Using a transcriptional inhA'-lacZ fusion, it was shown that inhA expression is activated at the onset of sporulation. However, the transcriptional start site of inhA is similar to sigma(A)-dependent promoters, and deletion of the sporulation-specific sigma factors sigma(F) or sigma(E) had no effect on inhA expression in B. subtilis. The DNA region upstream from inhA contains two genes encoding polypeptides similar to the SinI and SinR regulators of B. subtilis. SinR is a DNA-binding protein regulating gene expression and SinI inhibits SinR activity. Overexpression of the sin genes affects the expression of the inhA'-lacZ transcriptional fusion in B. thuringiensis: early induction of inhA expression was observed when sinI was overexpressed, whereas inhA expression was reduced in a strain overexpressing sinR, suggesting that inhA transcription is repressed, directly or indirectly, by SinR. inhA transcription was greatly reduced in B. thuringiensis and B. subtilis spo0A mutants. Analysis of the inhA'-lacZ expression in abrB and abrB-spo0A mutants of B. subtilis indicates that the Spo0A-dependent regulation of inhA expression depends on AbrB, which is known to regulate expression of transition state and sporulation genes in B. subtilis.