Molecular characterization of a novel chitinase from Bacillus thuringiensis subsp. kurstaki

Bacillus cereus sensu lato antimicrobial arsenal: An overview

The Bacillus cereus group contains genetically closed bacteria displaying a variety of phenotypic features and lifestyles. The group is mainly known through the properties of three major species: the entomopathogen Bacillus thuringiensis, the animal and human pathogen Bacillus anthracis and the foodborne opportunistic strains of B. cereus sensu stricto. Yet, the actual diversity of the group is far broader and includes multiple lifestyles. Another less-appreciated aspect of B. cereus members lies within their antimicrobial potential which deserves consideration in the context of growing emergence of resistance to antibiotics and pesticides, and makes it crucial to find new sources of antimicrobial molecules. This review presents the state of knowledge on the known antimicrobial compounds of the B. cereus group members, which are grouped according to their chemical features and biosynthetic pathways. The objective is to provide a comprehensive review of the antimicrobial range exhibited by this group of bacteria, underscoring the interest in its potent biocontrol arsenal and encouraging further research in this regard.

Bacterial endophytes inhabiting desert plants provide protection against seed rot caused by Fusarium verticillioides and promote growth in maize

BACKGROUND

Fusarium maize ear and root rot disease caused by Fusarium verticillioides has become one of the most serious fungal diseases associated with maize production. Due to their abilities to promote plant development and manage diseases, bacterial endophytes provide a more promising approach for treating this vascular disease.

RESULTS

This work was undertaken for the selection and identification of promising isolates as plant growth promoters and biocontrol agents against F. verticillioides in maize agroecosystems. A screening procedure consisting of in vitro and in situ tests was applied to 27 endophytic strains originating from desert plants: Euphorbia antiquorum, Calotropis procera, and Alcasia albida. In vitro studies indicated that the bacteria exhibited variable results in biocontrol, endophytism, and plant growth-promoting traits. In addition, in situ plant growth promotion and biocontrol experiments allowed the identification of the most promising bacterial endophytes. In vitro and in situ comparative study results indicated a low correlation. Our data revealed that in situ screening must be used as the method of selection of biocontrol agents against Fusarium ear and root rot disease. Based on in situ results, seven potent strains were selected and identified as Bacillus subtilis, Bacillus velezensis, Bacillus tequilensis, Stenotrophomonas maltophilia, and Klebsiella pneumoniae.

CONCLUSION

The results of this study showed that the selected strains seem to be promising candidates to be exploited as biofertilizers and biocontrol agents against Fusarium maize ear and root rot disease. © 2023 Society of Chemical Industry.

Comparative genome analysis of Bacillus thuringiensis strain HD521 and HS18-1

Bacillus thuringiensis (Bt) is an important biological insecticide used to management of different agricultural pests by producing toxic parasporal crystals proteins. Strain HD521 has an antagonistic effect against Rhizoctonia solani AG1IA, the causal agent of rice sheath blight. This strain with three cry7 genes can the formation of bipyramidal parasporal crystals (BPCs). BPCs are used for insecticidal activities against Henosepilachna vigintioctomaculata larva (Coleoptera). Strain HS18-1 contains different types of BPCs encoding genes and has effective toxicity for Lepidoptera and Diptera insects. Here we report the whole genome sequencing and assembly of HD521 and HS18-1 strains and analyzed the genome constitution covering virulence factors, types of plasmid, insertion sequences, and prophage sequences. The results showed that the genome of strain HD521 contains a circular chromosome and six circular plasmids, encoding eight types of virulence protein factors [Immune Inhibitor A, Hemolytic Enterotoxin, S-layer protein, Phospholipase C, Zwittermicin A-resistance protein, Metalloprotease, Chitinase, and N-acyl homoserine lactonase (AiiA)], four families of insertion sequence, and comprises six pro-phage sequences. The genome of strain HS18-1 contains one circular chromosome and nine circular plasmids, encoding five types of virulence protein factors [Hemolytic Enterotoxin, S-layer protein, Phospholipase C, Chitinase, and N-acyl homoserine lactonase (AiiA)] and four families of insertion sequence, and comprises of three pro-phage sequences. The obtained results will contribute to deeply understand the B. thuringiensis strain HD521 and HS18-1 at the genomic level.

Extracellular Antifungal Activity of Chitinase-Producing Bacteria Isolated From Guano of Insectivorous Bats

A reduction in the use of agrochemicals requires the development of either alternatives or complementary control methods in order to limit their dangerousness. An alternative is the biological control of fungi by bacteria. The fungal cell wall is a unique structure of the fungi, composed of glucan, chitin, and glycoproteins. Therefore, bacteria producing mycolytic enzymes, like chitinases, are of great interest to degrade fungal cell-wall components. The objectives of this work were to isolate chitinolytic bacteria from the guano of insectivorous bats (Tadarida brasiliensis) and to verify the presence of antifungal activities against phytopathogenic fungi. From the guano samples, 28 bacterial isolates were obtained, 70% of which presented chitinolytic activity. Four isolates were selected since they showed the highest values of chitinase activity, and they were characterized as belonging to Bacillus genus, by analyzing the 16S ribosomal RNA gene sequence. Cell-free supernatants of bacterial cultures were used in inhibition tests on 16 fungi: Alternaria and Colletotrichum acutatum were the most affected. Chitinase and antifungal activities were observed in the cell-free supernatant regardless of the culture medium used. Both activities were stable to heat and proteinase K treatments. Finally, when the culture medium was supplemented with 1 ml of cell-free supernatants (0.33%) and incubated for 120 h, the inhibition of hyphae formation and germination spores of reporter fungus were observed under light microscopy. These results suggest the feasibility of using cell-free supernatants as eco-friendly fungicides. The use of them may contribute to reducing the dose of toxic chemicals.

Two Novel Bacillus Strains (subtilis and simplex Species) with Promising Potential for the Biocontrol of Zymoseptoria tritici, the Causal Agent of Septoria Tritici Blotch of Wheat

Two novel Algerian field-collected isolates were selected for their antifungal activity against Zymoseptoria tritici (teleomorph Mycosphaerella graminicola). The novel strains, termed Alg.24B1 and Alg.24B2, were identified as Bacillus subtilis and Bacillus simplex since their respective nucleotide sequences of the 16S rRNA gene were 100% and 99.93% identical to those of B. subtilis and B. simplex, respectively. The antifungal activities of Alg.24B1 and Alg.24B2 were evaluated by the well diffusion method and compared to those of other Bacillus species. The maximum activity was obtained after two days of confrontation of the bacterial strain supernatants with the fungus for Alg.24B1 and three days for Alg.24B2. Furthermore, the metabolites responsible for the antifungal activity of both strains were detected by the investigation of either gene presence (PCR) or molecule production (activity detection of lytic enzymes and HPLC detection of lipopeptides). Overall, this study showed that in addition to their ability to produce lytic enzymes (protease and β-glucanase), both strains coproduce three types of lipopeptides viz. surfactin, iturin, and fengycin. Thus, the biofungicide activity of both strains may be a result of a combination of different mechanisms. Therefore, they had a great potential to be used as biocontrol agents to effectively manage septoria tritici blotch of wheat (STB).

Chitinases of Bacillus thuringiensis: Phylogeny, Modular Structure, and Applied Potentials

The most important bioinsecticide used worldwide is Bacillus thuringiensis and its hallmark is a rich variety of insecticidal Cry protein, many of which have been genetically engineered for expression in transgenic crops. Over the past 20 years, the discovery of other insecticidal proteins and metabolites synthesized by B. thuringiensis, including chitinases, antimicrobial peptides, vegetative insecticidal proteins (VIP), and siderophores, has expanded the applied value of this bacterium for use as an antibacterial, fungicidal, and nematicidal resource. These properties allow us to view B. thuringiensis not only as an entity for the production of a particular metabolite, but also as a multifaceted microbial factory. In particular, chitinases of B. thuringiensis are secreted enzymes that hydrolyze chitin, an abundant molecule in the biosphere, second only to cellulose. The observation that chitinases increase the insecticidal activity of Cry proteins has stimulated further study of these enzymes produced by B. thuringiensis. Here, we provide a review of a subset of our knowledge of B. thuringiensis chitinases as it relates to their phylogenetic relationships, regulation of expression, biotechnological potential for controlling entomopathogens, fungi, and nematodes, and their use in generating chitin-derived oligosaccharides (ChOGs) that possess antibacterial activities against a number of clinically significant bacterial pathogens. Recent advances in the structural organization of these enzymes are also discussed, as are our perspective for future studies.

Bio-efficacy of chitinolytic Bacillus thuringiensis isolates native to northwestern Indian Himalayas and their synergistic toxicity with selected insecticides

Pesticidal properties of Bacillus thuringiensis and its associated toxic proteins is an ever-growing science with potential implications in biological pest management. In the present study 80 Bacillus thuringiensis isolates native to Uttarakhand Himalayas were evaluated for chitinolytic activity and potent ones (11 isolates) were further subjected to multiphasic characterization for their antifungal, insecticidal and synergistic properties with selected chemical insecticides. Although all the 11 potent isolates were biologically active, only three isolates (VLBt27, VLBt109 and VLBt238) showed >90% inhibition in radial growth of 3 out of 4 tested plant pathogenic fungi (Rhizoctonia solani, Fusarium oxysporum, Alternaria pori and Pyricularia oryzae). The key antagonism was manifested in the form of disruptions in growing tips and uneven mycelial thickenings. In insect bioassays (against Helicoverpa armigera, Mythimna separata and Thysanoplusia orichalcea), no considerable direct mortality was observed. However, the larval weight reduction was prominent in four isolates (VLBt27, VLBt38, VLBt109 and VLBt135) which accounts to >75% in first instar larvae of H. armigera. Joint action of these four isolates with chemical insecticides showed an overall additive interaction against Brevicoryne brassicae and synergism against H. armigera. All the isolates were compatible with tested insecticides at their field recommended doses except for chlorpyriphos with around 130 kDa protein as chitinase. The study identified VLBt27 and VLBt109, two native isolates of B. thuringiensis with potential antagonistic activity and synergism as well. These isolates have possible implications as single strategy against two diverse pest problems (pathogenic fungi and phytophagous insect) of agriculture with a view of reduced pesticide application.

Isolation and Evaluation of New Antagonist Bacillus Strains for the Control of Pathogenic and Mycotoxigenic Fungi of Fig Orchards

Bacillus is an antagonistic bacteria that shows high effectiveness against different phytopathogenic fungi and produces various lytic enzymes, such as chitosanase, chitinase, protease, and gluconase. The aim of this study is to determine Bacillus spp. for lytic enzyme production and to evaluate the antifungal effects of the selected strains for biocontrol of mycotoxigenic and phytopathogenic fungi. A total of 92 endospore-forming bacterial isolates from the 24 fig orchard soil samples were screened for chitosanase production, and six best chitosanolytic isolates were selected to determine chitinase, protease, and N-acetyl-β-hexosaminidase activity and molecularly identified. The antagonistic activities of six Bacillus strains against Aspergillus niger EGE-K-213, Aspergillus foetidus EGE-K-211, Aspergillus ochraceus EGE-K-217, and Fusarium solani KCTC 6328 were evaluated. Fungal spore germination inhibition and biomass inhibition activities were also measured against A. niger EGE-K-213. The results demonstrated that Bacillus mojavensis EGE-B-5.2i and Bacillus thuringiensis EGE-B-14.1i were more efficient antifungal agents against A. niger EGE-K-213. B. mojavensis EGE-B-5.2i has shown maximum inhibition of the biomass (30.4%), and B. thuringiensis EGE-B-14.1i has shown maximum inhibition of spore germination (33.1%) at 12 h. This is the first study reporting the potential of antagonist Bacillus strains as biocontrol agents against mycotoxigenic fungi of fig orchads.

Characterization of a Bacillus thuringiensis chitinase that binds to cellulose and chitin

Bacillus thuringiensis is a Gram-positive soil bacterium that is known to be a bacterial biopesticide that produces insecticidal proteins called crystal proteins (Cry). In the insecticidal process, chitinases are suggested to perforate the peritrophic membrane barrier to facilitate the invasion of the Cry proteins into epithelial membranes. A chitinase gene from B. thuringiensis was successfully expressed in a soluble form in Escherichia coli, and the gene product was purified and characterized. The purified recombinant enzyme, BthChi74, hydrolyzed an artificial substrate, 4-nitrophenyl N,N′-diacetyl-β-d-chitobioside [4NP-(GlcNAc)₂], and the natural substrates, colloidal chitin and crystalline α-chitin, but it did not hydrolyze cellulose. BthChi74 exhibited catalytic activity under a weakly acidic to neutral pH range at 50 °C, and it was stable over a wide pH range for 24 h. Differential scanning fluorimetry (DSF) indicated a protein melting temperature (T_m) of 63.6 °C. Kinetic analysis revealed k_cat and K_M values of 1.5 s⁻¹ and 159 μM, respectively, with 4NP-(GlcNAc)₂ as a substrate. BthChi74 produced (GlcNAc)₂ and GlcNAc from colloidal chitin and α-chitin as substrates, but the activity toward the latter was lower than that toward the former. BthChi74 could bind similarly to chitin beads, crystalline α-chitin, and cellulose through a unique family 2 carbohydrate-binding module (CBM2). The structure–function relationships of BthChi74 are discussed in relation to other chitinases, such as Listeria chitinase, which possesses a family 5 carbohydrate-binding module (CBM5).

Bacillus thuringiensis and Bacillus weihenstephanensis Inhibit the Growth of Phytopathogenic Verticillium Species

Verticillium wilt causes severe yield losses in a broad range of economically important crops worldwide. As many soil fumigants have a severe environmental impact, new biocontrol strategies are needed. Members of the genus Bacillus are known as plant growth-promoting bacteria (PGPB) as well as biocontrol agents of pests and diseases. In this study, we isolated 267 Bacillus strains from root-associated soil of field-grown tomato plants. We evaluated the antifungal potential of 20 phenotypically diverse strains according to their antagonistic activity against the two phytopathogenic fungi Verticillium dahliae and Verticillium longisporum. In addition, the 20 strains were sequenced and phylogenetically characterized by multi-locus sequence typing (MLST) resulting in 7 different Bacillus thuringiensis and 13 Bacillus weihenstephanensis strains. All B. thuringiensis isolates inhibited in vitro the tomato pathogen V. dahliae JR2, but had only low efficacy against the tomato-foreign pathogen V. longisporum 43. All B. weihenstephanensis isolates exhibited no fungicidal activity whereas three B. weihenstephanensis isolates showed antagonistic effects on both phytopathogens. These strains had a rhizoid colony morphology, which has not been described for B. weihenstephanensis strains previously. Genome analysis of all isolates revealed putative genes encoding fungicidal substances and resulted in identification of 304 secondary metabolite gene clusters including 101 non-ribosomal polypeptide synthetases and 203 ribosomal-synthesized and post-translationally modified peptides. All genomes encoded genes for the synthesis of the antifungal siderophore bacillibactin. In the genome of one B. thuringiensis strain, a gene cluster for zwittermicin A was detected. Isolates which either exhibited an inhibitory or an interfering effect on the growth of the phytopathogens carried one or two genes encoding putative mycolitic chitinases, which might contribute to antifungal activities. This indicates that chitinases contribute to antifungal activities. The present study identified B. thuringiensis isolates from tomato roots which exhibited in vitro antifungal activity against Verticillium species.

The endochitinase ChiA Btt of Bacillus thuringiensis subsp. tenebrionis DSM-2803 and its potential use to control the phytopathogen Colletotrichum gloeosporioides

Bacillus thuringiensis subsp. tenebrionis DSM‐2803 has been studied extensively and spore/crystal mixtures of this strain are used widely in commercial products to control coleopteran pests. The endochitinase chiA Btt gene of B. thuringiensis subsp. tenebrionis DSM‐2803 was cloned and expressed in Escherichia coli. The recombinant 6x‐histidine tagged protein (rChiA Btt, ~74 kDa), was purified by a HiTrap Ni affinity column. The K_m of rChiA Btt was 0.847 μmol L⁻¹ and its optimal activity occurred at pH 7 and ~40°C. Most divalent cations reduced endochitinase activity but only Hg⁺² abolished activity of the enzyme. We report for the first time the characterization of a chitinase synthesized by B. thuringiensis subsp. tenebrionis DSM‐2803, and show that the purified rChiA74 Btt reduced the radial growth and increased the hyphal density of Colletotrichium gloeosporioides, the etiological agent of “anthracnose” in plants.

Enhanced nematicidal potential of the chitinase pachi from Pseudomonas aeruginosa in association with Cry21Aa

Nematodes are known to be harmful to various crops, vegetables, plants and insects. The present study reports that, chitin upregulates the activity of chitinase (20%) and nematicidal potential (15%) of Pseudomonas aeruginosa. The chitinase gene (pachi) from P. aeruginosa was cloned, and its nematicidal activity of pachi protein against Caenorhabditis elegans was studied. The mortality rate induced by pachi increased by 6.3-fold when in association with Cry21Aa from Bacillus thuringiensis. Pachi efficiently killed C. elegans in its native state (LC50 = 387.3 ± 31.7 μg/ml), as well as in association with Cry21Aa (LC50 = 30.9 ± 4.1 μg/ml), by degrading the cuticle, egg shell and intestine in a relatively short time period of 24 h. To explore the nematidal potential of chitinase, six fusion proteins were constructed using gene engineering techniques. The CHACry showed higher activity against C. elegans than others owing to its high solubility. Notably, the CHACry showed a synergistic factor of 4.1 versus 3.5 a mixture [1:1] of pachi and Cry21Aa. The present study has identified eco-friendly biological routes (e.g., mixed proteins, fusion proteins) with potent nematicidal activity, which not only can help to prevent major crop losses but also strengthen the agro-economy and increase gross crop yield.

YvoA and CcpA Repress the Expression of chiB in Bacillus thuringiensis

Bacillus thuringiensis produces chitinases, which are involved in its antifungal activity and facilitate its insecticidal activity. In our recent work, we found that a 16-bp sequence, drechiB (AGACTTCGTGATGTCT), downstream of the minimal promoter region of the chitinase B gene (chiB) was a critical site for the inducible expression of chiB in B. thuringiensis Bti75. In this work, we show that a GntR family transcriptional regulator (named YvoABt), which is homologous to YvoA of Bacillus subtilis, can specifically bind to the drechiB oligonucleotide sequences in vitro by using electrophoretic mobility shift assays (EMSAs) and isothermal titration calorimetry (ITC) assays. The results of quantitative real-time reverse transcription-PCR (qRT-PCR) and Western blotting indicated that deletion of yvoA caused an ∼7.5-fold increase in the expression level of chiB. Furthermore, binding of purified YvoABt to its target DNA could be abolished by glucosamine-6-phosphate (GlcN-6-P). We also confirmed, in the presence of the phosphoprotein Hpr-Ser₄₅-P, that purified CcpABt bound specifically to the promoter of chiB, which contains the "crechiB" sequence (ATAAAGCGTTTACA). According to the results of qRT-PCR and Western blotting, deletion of ccpA resulted in a 39-fold increase in the chiB expression level, and glucose no longer influenced the expression of chiB. We confirm that chiB is negatively controlled by both CcpABt and YvoABt in Bti75.

Characterisation of novel Bacillus thuringiensis isolates against Aedes aegypti (Diptera: Culicidae) and Ceratitis capitata (Diptera: Tephridae)

Bacillus thuringiensis is successfully used in pest management strategies as an eco-friendly bioinsecticide. Isolation and identification of new strains with a wide variety of target pests is an ever growing field. In this paper, new B. thuringiensis isolates were investigated to search for original strains active against diptera and able to produce novel toxins that could be used as an alternative for the commercial H14 strain. Biochemical and molecular characterization revealed a remarkable diversity among the studied strains. Using the PCR method, cry4C/Da1, cry30Ea, cry39A, cry40 and cry54 genes were detected in four isolates. Three strains, BLB355, BLB196 and BUPM109, showed feeble activities against Aedes aegypti larvae. Interestingly, spore-crystal mixtures of BLB361, BLB30 and BLB237 were found to be active against Ceratitis capitata with an LC50 value of about 65.375, 51.735 and 42.972 μg cm(-2), respectively. All the studied strains exhibited important mortality levels using culture supernatants against C. capitata larvae. This suggests that these strains produce a wide range of soluble factors active against C. capitata larvae.

Characterization of regulatory regions involved in the inducible expression of chiB in Bacillus thuringiensis

Expression of the chiB gene from Bacillus thuringiensis Bti75 was defined as inducible by the use of transcriptional fusions with the bgaB reporter gene. The transcription start site of the chiB gene was identified as the C base located 132 base pairs upstream of the start codon. Analysis of 5' and 3' deletions of the chiB promoter region revealed that the sequence from position -192 to +36 with respect to the transcription start site was necessary for wild-type levels of inducible expression of the chiB gene. The minimal promoter region for the expression of chiB gene was identified as the sequence from position -100 to +12. Furthermore, a 16-bp sequence (designated dre) downstream of the minimal promoter region of chiB was shown to be required for chitin induction. To confirm the function of this 16-bp sequence, 25 base substitutions were introduced into the dre site. Most of the mutations resulted in constitutive expression, or the efficiency of induction decreased. All mutations identified the dre sequence as a critical site for the inducible expression of chiB. In addition, the dre site was shown to interact with a sequence-specific DNA binding factor of strain Bti75 cultured in the absence of the inducer.

Selection and characterisation of an HD1-like Bacillus thuringiensis isolate with a high insecticidal activity against Spodoptera littoralis (Lepidoptera: Noctuidae)

BACKGROUND

Spodoptera littoralis (Boisduval) larvae are known by their susceptibility to Bacillus thuringiensis subsp. aizawai strains. In order to prevent the appearance of B. thuringiensis (Bt) resistance and to develop economical Bt-based biopesticides, the selection and the characterisation of a B. thuringiensis isolate toxic against S. littoralis larvae and overproducing δ-endotoxins were investigated.

RESULTS

Among 124 Tunisian B. thuringiensis isolates assessed against S. littoralis larvae, four isolates showed toxicity similar to and higher than the toxicity of the aizawai strain HD133 and the kurstaki strain HD1 respectively. The plasmid pattern of the selected isolates was similar to that of HD1. Polymerase chain reaction (PCR) analysis using specific primers revealed that these isolates present different gene contents. The only detected gene encoding Spodoptera-specific toxin was cry9. The selected isolates were found to produce bipyramidal and cubic crystals. The assessment of δ-endotoxin production by these isolates showed that BUPM28 produced 43.71 and 80.81% more δ-endotoxin than HD1 and HD133 respectively. The application of osmotic or heat shock stress on the BUPM28 isolate made it possible to enhance δ-endotoxin production by 22 and 23% respectively.

CONCLUSION

On the basis of its potent insecticidal activity and its high level of δ-endotoxin production, the BUPM28 isolate can be considered to be an effective alternative for the control of S. littoralis.

The direct repeat sequence upstream of Bacillus chitinase genes is cis-acting elements that negatively regulate heterologous expression in E. coli

To explore the influence of the direct repeat sequence (DRS) in Bacillus chitinase genes on heterogonous expression in Escherichia coli, we cloned and sequenced the entire open reading frame (ORF) and upstream sequences of the chitinase B (chiB) and chitinase MY75 (chiMY75) from Bacillus thuringiensis and Bacillus licheniformis. A pair of 8-bp DRS was found upstream of each chi gene. Chi ORFs with a series of truncated DRS were cloned and transformed into E. coli XL-Blue. The activity of the transformants without the DRS were significantly higher in chitinase assays than transformants containing the DRS. SDS-PAGE showed that part and full deletion of the DRS increased chi gene expression by approximately 1.7 and 3.8-fold, respectively. Northern blotting revealed deletion of the DRS regions increased chiB and chiMY75 mRNA expression. Specific binding of DNA-binding factors in the E. coli cell lyaste was observed to both the chiB and chiMY75 promoter regions and DRS elements. This is the first investigation to demonstrate that heterologous expression of Bacillus chi genes in E. coli is negatively regulated by their upstream DRS regions, which act as cis-acting elements.

Chitinase production by Bacillus thuringiensis and Bacillus licheniformis: their potential in antifungal biocontrol

Thirty bacterial strains were isolated from the rhizosphere of plants collected from Egypt and screened for production of chitinase enzymes. Bacillus thuringiensis NM101-19 and Bacillus licheniformis NM120-17 had the highest chitinolytic activities amongst those investigated. The production of chitinase by B. thuringiensis and B. licheniformis was optimized using colloidal chitin medium amended with 1.5% colloidal chitin, with casein as a nitrogen source, at 30°C after five days of incubation. An enhancement of chitinase production by the two species was observed by addition of sugar substances and dried fungal mats to the colloidal chitin media. The optimal conditions for chitinase activity by B. thuringiensis and B. licheniformis were at 40°C, pH 7.0 and pH 8.0, respectively. Na(+), Mg(2+), Cu(2+), and Ca(2+) caused enhancement of enzyme activities whereas they were markedly inhibited by Zn(2+), Hg(2+), and Ag(+). In vitro, B. thuringiensis and B. licheniformis chitinases had potential for cell wall lysis of many phytopathogenic fungi tested. The addition of B. thuringiensis chitinase was more effective than that of B. licheniformis in increasing the germination of soybean seeds infected with various phytopathogenic fungi.

Construction of a promoter-probe vector for Bacillus thuringiensis: the identification of cis-acting elements of the chiA locus

The expression and application of Bacillus thuringiensis (Bt) chitinase genes have been extensively investigated. However, little information is available regarding the regulation of chitinase gene expression in Bt. In this study, a shuttle promoter-probe vector was constructed incorporating the thermostable β-galactosidase gene bgaB of B. stearothermophilus as the reporter for the study of Bt promoters. Using this plasmid, the activity of the chiA gene promoter in Bt was investigated. Deletion analysis of the putative chiA promoter region revealed that the sequence located ~75 bp DNA from positions -116 to -42, with respect to the translation start site, is the core promoter of chiA gene. Furthermore, a site for chitin induction was identified near position -36. This site for negative regulation was indicated downstream of the RNA polymerase binding sites of the promoter of chiA. The expression of chiA started in cell grown for about 6 h and reached the maximum after 60 h of incubation. Induction of chiA expression by chitin was demonstrated by an increase in β-galactosidase activity of ~2.5-fold.

Induction of defense-related enzymes in soybean leaves by class IId bacteriocins (thuricin 17 and bacthuricin F4) purified from Bacillus strains

We have recently discovered a new class of bacteriocin (class IId) which stimulates plant growth in a way similar to Nod factors. Nod factors have been shown to provoke aspects of plant disease resistance. We investigated the effects of bacteriocins [thuricin 17 (T17) and bacthuricin F4 (BF4)] on the activities of phenylalanine ammonia lyase (PAL), guaiacol peroxidase (POD), ascorbate peroxidase (APX), superoxide dismutase (SOD), and polyphenol oxidase (PPO). Bacteriocin solutions were fed into the cut stems of soybean (Glycine max L. Merr. cv. OAC Bayfield) seedlings at the first trifoliate stage. PAL activity in T17 treated leaves was the highest at 72h after treatment and was 75.5% greater than the control at that time. At 72h after treatment POD activities in T17 and BF4 treated leaves increased by 72.7 and 91.3%, respectively, as compared with the control treatment. APX activity was 52.3 and 49.6% respectively, greater than the control in T17 and BF4 treated leaves at 72h after treatment. SOD activity in T17 treated leaves was the highest at 72h after treatment and was 26.0% greater than the control at that time. SOD activity was 70.5 and 60.2% greater, respectively, than the control in T17 and BF4 treated leaves, at 72h. Using PAGE we found that one APX isozyme (28kDa isoform) showed the strongest induction in all bacteriocin treated leaves at 72h. Activity of the seven SOD isozymes was increased by both bacteriocins, relative to the control treatment. The 33kDa PPO isozyme was induced strongly by both bacteriocins, relative to the control treatment. These results indicate that class IId bacteriocins can act as an inducer of plant disease defense-related enzymes and may be acting through mechanisms similar to Nod factors.

Swapping the chitin-binding domain in Bacillus chitinases improves the substrate binding affinity and conformational stability

Chitinase from Bacillus thuringiensis and Bacillus licheniformis consisting of an N-terminal catalytic domain (GH18) and a C-terminal chitin-binding domain (ChBD), were cloned and characterised. In order to study the importance of individual domains, chimeric chitinases (BtGH-BliChBD and BliGH-BtChBD) were constructed using domain swapping as a strategy to exchange the CBD of BtGH-ChBD with that of BliGH-ChBD and vice versa. Both chimeric chitinases showed increased affinity to colloidal chitin. BtGH-BliChBD was different from the three other chitinases studied concerning optimum temperature and pH. Additionally, BtGH-BliChBD and BliGH-BtChBD showed significant improvement in functional stability, conformational stability, and binding ability towards insoluble chitinous substrates compared to those of the native chitinases.

Induced production of chitinase to enhance entomotoxicity of Bacillus thuringiensis employing starch industry wastewater as a substrate

Induced production of chitinase during bioconversion of starch industry wastewater (SIW) to Bacillus thuringiensis var. kurstaki HD-1 (Btk) based biopesticides was studied in shake flask as well as in computer-controlled fermentors. SIW was fortified with different concentrations (0%; 0.05%; 0.1%; 0.2%; 0.3% w/v) of colloidal chitin and its consequences were ascertained in terms of Btk growth (total cell count and viable spore count), chitinase, protease and amylase activities and entomotoxicity. At optimum concentration of 0.2% w/v colloidal chitin, the entomotoxicity of fermented broth and suspended pellet was enhanced from 12.4x10(9) (without chitin) to 14.4x10(9) SBU/L and from 18.2x10(9) (without chitin) to 25.1x10(9) SBU/L, respectively. Further, experiments were conducted for Btk growth in a computer-controlled 15 L bioreactor using SIW as a raw material with (0.2% w/v chitin, to induce chitinase) and without fortification of colloidal chitin. It was found that the total cell count, spore count, delta-endotoxin concentration (alkaline solubilised insecticidal crystal proteins), amylase and protease activities were reduced whereas the entomotoxicity and chitinase activity was increased with chitin fortification. The chitinase activity attained a maximum value at 24 h (15 mU/ml) and entomotoxicity of suspended pellet reached highest (26.7x10(9) SBU/L) at 36 h of fermentation with chitin supplementation of SIW. In control (without chitin), the highest value of entomotoxicity of suspended pellet (20.5x10(9) SBU/L) reached at 48 h of fermentation. A quantitative synergistic action of delta-endotoxin concentration, spore concentration and chitinase activity on the entomotoxicity against spruce budworm larvae was observed.