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

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.

Three-step biocatalytic reaction using whole cells for efficient production of tyramine from keratin acid hydrolysis wastewater

Tyramine has been paid more attention in recent years as a significant metabolite of tyrosine and catecholamine drug and an intermediate of medicinal material and some drugs. In this study, an effective, green, and three-step biocatalytic synthesis method for production of tyramine starting from serine in keratin acid hydrolysis wastewater was developed and investigated. Serine deaminase from Escherichia coli was first combined with tyrosine phenol-lyase from Citrobacter koseri, to convert L-serine to L-tyrosine. L-Tyrosine can then be decarboxylated to tyramine by tyrosinede carboxylase from Lactobacillus brevis. All these enzymes originated from recombinant whole cells. Serine deaminaseand tyrosine phenol-lyase could efficiently convert L-serine in wastewater to L-tyrosine at pH 8.0, 37 °C, and Triton X-100 of 0.04% when tyrosine phenol-lyase and its corresponding substrates were sequentially added. Tyrosine conversion rate reached 98 % by L-tyrosine decarboxylase. In scale-up study, the conversion yield of L-serine in wastewater to tyrosine was up to 89 %. L-Tyrosine was decarboxylated to tyramine with a high yield 94 %. Tyramine hydrochloride was obtained with a total yield 84 %. This study has provided an efficient way of recycling keratin acid hydrolysis wastewater to produce tyramine.

Genome Sequence of Bacillus thuringiensis Strain Btm27, an Egyptian Isolate Highly Toxic to Cotton Leafworm

Bacillus thuringiensis is a potent microbial control agent against insect pests. Here, we present the draft genome of the Egyptian strain Btm27 that shows high toxicity toward the cotton leafworm. The genome contains three insecticidal genes cry1Ac9, cry2Ab1, and vip3V that have been implicated in conferring toxicity toward lepidoptera.

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.

Mathematical relationships between spore concentrations, delta-endotoxin levels, and entomotoxicity of Bacillus thuringiensis preparations produced in different fermentation media

Mathematic relationships between spore concentrations, delta-endotoxin concentrations and entomotoxicity (Tx) of Bacillus thuringiensis var. kurstaki HD-1 (Btk HD-1) preparations produced in six different media were analysed. The relationship between delta-endotoxin and spore concentration and SpTx-spore (specific Tx per 1000 spore) and spore concentration produced in the different media (starch industry wastewater (SIW) with total solids (TS) concentration of 15g/L, SIW with TS of 30g/L, SIW supplemented with 0.2% (w/v) colloidal chitin, SIW supplemented with 1.25% (w/v) cornstarch and 0.2% (v/v) Tween 80, secondary sludge, and semi-synthetic medium) strictly followed the Power law. Tx and delta endotoxin concentration followed the exponential relation whereas a definite relation between Tx and spore concentration could not be established. Spore and delta-endotoxin produced at the early time (12h) during fermentation might be more toxic than those produced during latter period of fermentation irrespective of media used. Tx and delta-endotoxin concentration exhibited a semi-log linear relationship. Based on these findings, delta-endotoxin concentration can be determined rapidly to monitor the progress of the biopesticide production process.