Whole Genome Sequencing Analysis of Bacillus thuringiensis GR007 Reveals Multiple Pesticidal Protein Genes

Hybrid de novo whole genome assembly of lipopeptide producing novel Bacillus thuringiensis strain NBAIR BtAr exhibiting antagonistic activity against Sclerotium rolfsii

Bacillus thuringiensis Berliner is recognized as a predominant bioinsecticide but its antifungal potential has been relatively underexplored. A novel B. thuringiensis strain NBAIR BtAr was isolated and morphologically characterized using light and scanning electron microscopy, revealing presence of bipyramidal, cuboidal, and spherical parasporal crystals. The crude form of lipopeptides was extracted from NBAIR BtAr and assessed for its antagonistic activity in vitro, and demonstrated 100 % inhibition of Sclerotium rolfsii Sacc. at a minimum inhibitory concentration of 50 μL of the crude lipopeptide extract per mL of potato dextrose agar. To identify the antagonistic genes responsible, we performed whole genome sequencing of NBAIR BtAr, revealing the presence of circular chromosome of 5,379,913 bp and 175,362 bp plasmid with 36.06 % guanine-cytosine content and 5814 protein-coding sequences. Average nucleotide identity and whole genome phylogenetic analysis delineated the NBAIR BtAr strain as konkukian serovar. Gene ontology analysis revealed associations of 1474, 1323, and 1833 genes with biological processes, molecular function, and cellular components, respectively. Antibiotics & secondary metabolite analysis shell analysis of the whole genome yielded secondary metabolites biosynthetic gene clusters with 100 %, 85 %, 40 %, and 35 % similarity for petrobactin, bacillibactin, fengycin, and paenilamicin, respectively. Also, novel biosynthetic gene clusters, along with antimicrobial genes, including zwittermicin A, chitinase, and phenazines, were identified. Moreover, the presence of eight bacteriophage sequences, 18 genomic islands, insertion sequences, and one CRISPR region indicated prior occurrences of genetic exchange and thus improved competitive fitness of the strain. Overall, the whole genome sequence of NBAIR BtAr is presented, with its taxonomic classification and critical genetic attributes that contribute to its strong antagonistic activity against S. rolfsii.

Bacillus thuringiensis Cry14A family proteins as novel anthelmintics against gastrointestinal nematode parasites

Bacillus thuringiensis crystal (Cry) proteins have been expressed in commercial transgenic crops for nearly 30 years, providing safe and effective control of insect pests and significantly reducing the application of hazardous chemical pesticides. B. thuringiensis crystal proteins have also been shown to target parasitic nematodes, including plant parasitic nematodes. Recently, transgenic soybean crops expressing Cry14Ab have been shown to provide control against the soybean cyst nematode Heterodera glycines, marking the first time a crystal protein is being commercialized in transgenic crops for control of a nematode pest. However, apart from H. glycines and the free-living nematode, Caenorhabditis elegans, the breadth of nematode activity of Cry14Ab, e.g., against gastrointestinal parasitic nematodes (GINs), has not been reported. Here we study the efficacy of Cry14Ab against a wide range of gastrointestinal nematode parasites (GINs) in vitro and in vivo. We find that Cry14Ab is effective in vitro against the barber's pole worm Haemonchus contortus larvae, small strongyles cyathostomin larvae, the hookworm Ancylostoma ceylanicum adults, the roundworm Ascaris suum L4 larvae, and the whipworm Trichuris muris adults. In rodents infected with GIN parasites, Cry14Ab is effective as an in vivo anthelmintic against the hookworms A. ceylanicum and N. americanus, against the mouse parasite Heligmosomoides polygyrus bakeri, and against the roundworm A. suum. Cry14Ab also variably reduces the reproduction of the whipworm T. muris in vivo. Using optimized profile Markov Models, we looked for other putative anthelmintic Cry proteins and, within this list, identified a Bt crystal protein, GenBank accession no. MF893203, that we produced and demonstrated intoxicated GINs. This protein, with 90% amino acid identity to Cry14Ab, is active against C. elegans, A. ceylanicum adults, and A. suum L4 larvae in vitro. MF893203 was given the official designation of Cry14Ac. Cry14Ac is also an effective in vivo anthelmintic against A. ceylanicum hookworms in hamsters and intestinal A. suum in mice. Taken together, our results demonstrate that Cry14Ab and Cry14Ac have wide therapeutic utility against GINs.

Bioefficacy and molecular characterization of Bacillus thuringiensis strain NBAIR BtGa against greater wax moth, Galleria mellonella L

Galleria mellonella, the greater wax moth has always been an important pest against honeybees and has remained a nightmare for beekeeping farmers. Management of G. mellonella in live honeybee colonies is very difficult because most current management practices can destroy whole honeybee colonies. In the present study, experiments were conducted to isolate and characterize Bacillus thuringiensis from infected greater wax moth cadavers and to evaluate their biocontrol ability against G. mellonella. The bioefficacy of these isolates has been evaluated against greater wax moth along with the standard strain HD-1. Among all the strains tested, NBAIR BtGa demonstrated higher efficacy compared to other strains, with an LC50 value of 125.17 µg/ml, whereas HD-1 exhibited a significantly higher LC50 value of 946.61 µg/ml. Considering the economic importance of NBAIR BtGa we performed whole genome sequencing of this strain resulting in the identification of a genome size of 5.96 Mb consisting of 6888 protein-coding genes. Gene ontology analysis categorized these genes into three groups based on their roles, i.e., biological functions (2169 genes), cellular components (1900 genes), and molecular functions (2774 genes). Through insecticidal toxicity-related genes (ITRG) profiling of our strain across the genome by Bt toxin scanner and cry processor resulted in the identification of several Cry proteins namely Cry1Ab11, Cry1Ia44, Cry1Aa2, Cry2Af1, Cry1Da2, Cry1Eb1, Cry1Ab5, Cry1Cb2, Cry1Ac2. Besides Cry proteins, other ITRG genes, viz. Vip3Bb2, Zwittermicin A resistance proteins, Chitinase C, Mpp46Ab1, immune inhibitor A, Bmp1, Vpb4Ca1, and Spp1Aa1 were also reported, which show toxicity against lepidopteran pests. The studies were also conducted to test the biosafety of Bt toxins against honeybee larvae and adults, which showed strain NBAIR BtGa was more than 99% safer for honeybee larvae as well as adults. Thus, the data generated ascertains its effectiveness as a biocontrol agent and it can be used further for the development of bio formulation for the management of G. mellonella in honeybee colonies.

Mosquitocidal toxin-like islands in Bacillus thuringiensis S2160-1 revealed by complete-genome sequence and MS proteomic analysis

Here, we present the whole genome sequence of Bt S2160-1, a potential alternative to the mosquitocidal model strain, Bti. One chromosome genome and four mega-plasmids were contained in Bt S2160-1, and 13 predicted genes encoding predicted insecticidal crystal proteins were identified clustered on one plasmid pS2160-1p2 containing two pathogenic islands (PAIs) designed as PAI-1 (Cry54Ba, Cry30Ea4, Cry69Aa-like, Cry50Ba2-like, Cry4Ca1-like, Cry30Ga2, Cry71Aa-like, Cry72Aa-like, Cry70Aa-like, Cyt1Da2-like and Vpb4C1-like) and PAI-2 (Cyt1Aa-like, and Tpp80Aa1-like). The clusters appear to represent mosquitocidal toxin islands similar to pathogenicity islands. Transcription/translation of 10 of the 13 predicted genes was confirmed by whole-proteome analysis using LTQ-Orbitrap LC-MS/MS. In summary, the present study identified the existence of a mosquitocidal toxin island in Bacillus thuringiensis, and provides important genomic information for understanding the insecticidal mechanism of B. thuringiensis.

More than just an insect killer: The non-insecticidal activities of Bacillus thuringiensis with biotechnological potential

Bacillus thuringiensis (Bt) is known for the biological control of important insect pests, but scientific advances have revealed several interesting characteristics, in addition to this classical function as a bioinsecticide. To investigate the current knowledge about these non-insecticidal activities, a systematic research on primary data in the scientific literature was conducted on alternative functions of Bt with biotechnological potential. Out of a total of 140 articles selected, 15 non-insecticidal Bt activities were found. Publications related to this topic are available since 1971, and different metadata were reported, such as biomolecules and genes involved in Bt performances in non-insecticidal bioactivities. A total of 11 Bt activities with different effect measures (response variables) were identified, with an average of 48 distinct Bt strains evaluated per activity. Approximately 81.2% of all identified experiments/tests deal with the direct effects of Bt on target cells/organisms, with 36.3% of the strains within these studies tested for antibacterial action; of all microbial targets tested, 92.8% are bacteria, which led to 75.2% of the experimental conditions for all direct activities being performed in vitro. Regarding indirect Bt activities, 67.6% of these studies reported tritrophic Bt-plant-pathogen interactions. Bioremediation also appears as a relevant Bt activity being investigated in-depth. Alternative Bt activities offer innovative ways of developing biotechnology for different areas of anthropic interest; hence, we also focus on the possibility of finding multifunctional strains of Bt, as this may be advantageous from a bioeconomic point of view. Our findings are discussed in terms of research trends, aspects, details and depth of the current knowledge on alternative non-insecticidal Bt traits. We also discuss the potential application of this science for useful technological developments, aiming at solving issues related to human health, sustainable agriculture and environmental preservation/restoration.

Multiple cry Genes in Bacillus thuringiensis Strain BTG Suggest a Broad-Spectrum Insecticidal Activity

The properties of Bacillus thuringiensis strains as a biopesticide with potent action against moths, beetles, and mosquitoes have been known for decades, with individual subspecies showing specific activity against a particular pest. The aim of the present work is to characterize strains that can be used for broad-spectrum pest control in agriculture. Twenty strains of B. thuringiensis were isolated from Bulgarian soil habitats. The strains were screened for genes encoding 12 different crystal (Cry) endotoxins by PCR with specific primer pairs. Seven of the isolates contained cry genes in their genomes. B. thuringiensis strains PL1, PL3, and PL20 contained at least three different cry genes, while B. thuringiensis serovar galleriae BTG contained at least four. Moreover, scanning electron microscopy (SEM) investigation revealed the production of bipyramidal (PL1, PL3, PL20), polygonal (PL1), cubic (BTG), and spherical crystals (BTG and PL20). Potentially containing the most cry genes, the BTG genome was sequenced and annotated. It comprises 6,275,416 base pairs, does not contain plasmids, has a GC content of 35.05%, and contained 7 genes encoding crystal toxins: cry1Ab35, cry1Db, cry1Fb, cry1Ib, cry2Ab, cry8Ea1, and cry9Ba. This unique combination would possibly enable the simultaneous pesticidal action against pest species from orders Lepidoptera, Coleoptera, Diptera, and Hemiptera, as well as class Gastropoda. Whole-genome sequencing provided accurate information about the presence, localization, and classification of Cry toxins in B. thuringiensis BTG, revealing the great potential of the strain for the development of new broad-spectrum bio-insecticides.

Structural changes upon membrane insertion of the insecticidal pore-forming toxins produced by Bacillus thuringiensis

Different Bacillus thuringiensis (Bt) strains produce a broad variety of pore-forming toxins (PFTs) that show toxicity against insects and other invertebrates. Some of these insecticidal PFT proteins have been used successfully worldwide to control diverse insect crop pests. There are several studies focused on describing the mechanism of action of these toxins that have helped to improve their performance and to cope with the resistance evolved by different insects against some of these proteins. However, crucial information that is still missing is the structure of pores formed by some of these PFTs, such as the three-domain crystal (Cry) proteins, which are the most commercially used Bt toxins in the biological control of insect pests. In recent years, progress has been made on the identification of the structural changes that certain Bt insecticidal PFT proteins undergo upon membrane insertion. In this review, we describe the models that have been proposed for the membrane insertion of Cry toxins. We also review the recently published structures of the vegetative insecticidal proteins (Vips; e.g. Vip3) and the insecticidal toxin complex (Tc) in the membrane-inserted state. Although different Bt PFTs show different primary sequences, there are some similarities in the three-dimensional structures of Vips and Cry proteins. In addition, all PFTs described here must undergo major structural rearrangements to pass from a soluble form to a membrane-inserted state. It is proposed that, despite their structural differences, all PFTs undergo major structural rearrangements producing an extended α-helix, which plays a fundamental role in perforating their target membrane, resulting in the formation of the membrane pore required for their insecticidal activity.

Biodegradation of Pine Processionary Caterpillar Silk Is Mediated by Elastase- and Subtilisin-like Proteases

Pine processionary caterpillar nests are made from raw silk. Fibroin protein is the main component of silk which, in the case of pine processionary caterpillar, has some unusual properties such as a higher resistance to chemical hydrolysis. Isolation of microorganisms naturally present in silk nests led to identification of Bacillus licheniformis and Pseudomonas aeruginosa strains that in a defined minimal medium were able to carry out extensive silk biodegradation. A LasB elastase-like protein from P. aeruginosa was shown to be involved in silk biodegradation. A recombinant form of this protein expressed in Escherichia coli and purified by affinity chromatography was able to efficiently degrade silk in an in vitro assay. However, silk biodegradation by B. licheniformis strain was mediated by a SubC subtilisin-like protease. Homologous expression of a subtilisin Carlsberg encoding gene (subC) allowed faster degradation compared to the biodegradation kinetics of a wildtype B. licheniformis strain. This work led to the identification of new enzymes involved in biodegradation of silk materials, a finding which could lead to possible applications for controlling this pest and perhaps have importance from sanitary and biotechnological points of view.