Structural characterization and heterologous expression of a new cyt gene cloned from Bacillus thuringiensis.

Bacillus thuringiensis (Bt) strains produce Cry (crystal) and Cyt (cytolytic) proteins belonging to the group of bacterial toxins known as pore-forming toxins (PFTs), which interact with midgut cells of target insects to create pores, disruption of ion homeostasis and eventual death. PFTs have synergistic insecticidal activities and have been used as biopesticides against agriculturally important insects. Identification of new Cyt proteins is important because of their specific toxicity towards hemipteran pests, against which the Cry proteins are not effective. We have structurally characterized a cyt (cyt1007) gene from an Indian Bt isolate SK-1007. The presence of a "Bacillus thuringiensis toxin" domain and maximum identity of 36% with Cyt2Ca in the deduced amino acid sequence indicated Cyt1007 protein to be a new member of Cyt family. Three dimensional (3D) modeling (PMDB ID: PM0081490) revealed that it adopts a typical ferredoxin-like fold, and is composed of a single domain of α/ß architecture, in which a single ß sheet is surrounded by two α helical layers. The putative lipid binding site and probable mode of action of Cyt1007 protein were predicted through comparative analysis with other Cyt toxins and their distant homologs Evf (Erwinia virulence factor) and VVA2 (Volvatoxin A2). Heterologous expression of cyt1007 gene as a 25 kDa protein in Escherichia coli was achieved at high levels in both soluble and insoluble fractions. Affinity chromatography-based purification yielded 83.6% purified Cyt1007 protein, which can be used for downstream applications for the investigation of its toxicity. Graphical abstract Steps in the structural characterization and heterologous expression of a new cyt gene cloned from Bacillus thuringiensis.

A novel cry52Ca1 gene from an Indian Bacillus thuringiensis isolate is toxic to Helicoverpa armigera (cotton boll worm).

The novel cry52Ca1 gene from an Indian Bacillus thuringiensis (Bt) isolate was cloned in an expression vector (pET301/CT-DEST, 6xHis). The gene expressed as a ∼77.2 kDa protein in E. coli BL21-CodonPlus (DE3)-RIPL cells upon induction with isopropyl-thio-galactoside (IPTG) for 18 h at 28 °C. Cry52Ca1 protein was toxic to Helicoverpa armigera (cotton bollworm) neonate larvae (LC50 36.66 µg per ml and MIC50 3.051 µg per ml) in diet-based laboratory assays. This gene has potential for deployment in insect-resistant transgenic crops.

Pool deconvolution approach for high-throughput gene mining from Bacillus thuringiensis.

Novel genes from Bacillus thuringiensis (Bt) are required for effective deployment in agriculture, human health, and forestry. In an improvement over conventional PCR-based screening, next generation sequencing (NGS) has been used for identification of new genes of potential interest from Bt strains, but cost becomes a constraint when several isolates are to be sequenced. We demonstrate the potential of a DNA pooling strategy known as pool deconvolution to identify commercially important toxin genes from 36 native Bt isolates. This strategy is divided into three steps: (a) DNA pooling, (b) short read sequence assembly followed by gene mining, and (c) host isolate identification. With this approach, we have identified insecticidal protein (ip) genes including nine three-domain (3D) cry genes, three cyt-type genes, three mtx genes (mosquitocidal toxin), and one bin and vip-type gene each. Three cry-type and three cyt-type genes were cloned, out of which, two cry-type genes, ip11 and ip13, were named as cry4Ca2 and cry52Ca1, respectively by the Bacillus thuringiensis nomenclature committee ( http://www.biols.susx.ac.uk/Home/Neil_Crickmore/BT/ ). Our results show that the pool deconvolution approach is well suited for high-throughput gene mining in bacteria.