Characterization of a new highly mosquitocidal isolate of Bacillus thuringiensis – An alternative to Bti?

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.

Characterization of a novel Bacillus thuringiensis toxin active against Aedes aegypti larvae

Some Bacillus thuringiensis (Bt) strains produce dipteran-active toxins and can control larval mosquitoes. We identified a novel mosquitocidal toxin named Xpp81Aa1 with the thioredoxin domain from Bt strain HSY204. This toxin has very little sequence similarity to the three-domain Cry toxin and Cyt toxins and has significant toxicity to Aedes aegypti larvae. A safety assessment indicated that the Xpp81Aa1 toxin has no cytocidal activity against red blood cells and did not induce allergic reactions. The Xpp81Aa1 toxin exhibited a synergistic effect in combination with Cry2Aa and Cry4Aa protein toxins. Thus, the Xpp81Aa1 toxin could be a good candidate for mosquito control applications to reduce the mosquito-borne disease.

Bacillus thuringiensis novel toxin Epp is toxic to mosquitoes and prodenia litura larvae

As a pathogenic bacterium, Bacillus thuringiensis (Bt) has become an alternative to chemical insecticides in commercial agricultural to control forestry pests and mosquitoes. To prevent pest resistance, many novel Bt strains have been isolated. Strain S3580-1 (WGS: VHPX0000000) used in this research and originally isolated from Hainan Qixianling National Forest Park (China) showed significant toxicity to Culex pipiens pallens. Here, using whole genome sequencing, assembly, and bioinformatics analysis, the predicted S3580-1CG_5163 (GenBank Accession No. MK124137) gene-encoded protein was found to share low homology with known toxins designated by the Bt toxin nomenclature system. It was considered to be an ETX/MTX2-type toxin and was designated Epp. Bioinformatics analysis showed that the predicted S3580-1CG_5163 gene-encoded protein Epp shared low identity with other known toxic protein sequences containing Cry-ETX/MTX conserved domains at the amino acid level, but significant similarity at the structural level. In addition, bioassays showed that Epp was toxic against Spodoptera litura (LC₅₀ 296.133 μg/mL; 95% FL 200.555-471.318 μg/mL) and Cx. pipiens pallens (LC₅₀ 322.193 μg/mL; 95% FL 238.217-477.243 μg/mL). On pathological observation, the peritrophic membrane of Cx. pipiens pallens larvae was degraded causing the midgut structure to become incomplete, resulting in larval death. Further bioassays are required to fully elucidate the insecticidal spectrum of the ETX/MTX2-type toxin Epp, and thereby provide future research directions.

Genome of Bacillus sp. strain QHF158 provides insights into its parasporal inclusions encoded by the S-layer gene

Bacillus sp. strain QHF158, a Gram-positive, spore-forming and parasporal crystal-secreting bacterium, was isolated from soil of Limushan National Forest Park in China. Here we present the significant feature of parasporal inclusions of this organism, together with the draft genome sequence and annotation. Phylogenetic analysis suggested that strain QHF158 is possibly a novel species, most closely related to Bacillus mycoides. Genome annotation results revealed that strain QHF158 did not contain any typical Cry or Cyt toxin coding gene. Furthermore, the mass spectrometry analyses demonstrated that the parasporal crystalline inclusions were encoded by the orf_05273 gene, with 95% similarity to the S-layer protein (SLP) EA1 of B. mycoides, which indicated that the parasporal crystal from Bacillus sp. strain QHF158 was mainly formed by SLP, instead of the typical Cry or Cyt toxin proteins.

Four New Insecticidal Xanthene Derivatives from the Mangrove-Derived Fungus Penicillium sp. JY246

Four new xanthene derivatives, penicixanthenes A-D (1-4), and one known compound 5 were isolated from a marine mangrove endophytic fungus Penicillium sp. JY246 that was obtained from the stem of Ceriops tagal. Their structures were determined by detailed NMR, MS spectroscopic data, modified Mosher's method, and calculated electronic circular dichroism data. All of the isolated compounds were examined for insecticidal activity. Compounds 2 and 3 showed growth inhibition activity against newly hatched larvae of Helicoverpa armigera Hubner with the IC₅₀ values 100 and 200 μg/mL, respectively, and compounds 1, 3, and 4 showed insecticidal activity against newly hatched larvae of Culex quinquefasciatus with LC₅₀ values of 38.5 (±1.16), 11.6 (±0.58), and 20.5 (±1) μg/mL, respectively. The four xanthene derivatives have the potential to be developed as new biopesticides.

Bioactive Lactones from the Mangrove-Derived Fungus Penicillium sp. TGM112

Three new lactones penicilactones A−C (1−3) were obtained from the mangrove-derived fungus Penicillium sp. TGM112. Their structures and absolute configurations were determined by detailed NMR, MS spectroscopic data, Mo₂(OAc)₄-induced electronic circular dichroism (ECD), and circular dichroism (CD) spectroscopy. Compound 1 showed antibacterial activity against Staphylococcus aureus with an MIC value of 6.25 μg/mL. Compound 2 showed insecticidal activity against newly hatched larvae of Culex quinquefasciatus with the LC₅₀ value of 78.5 (±0.58) μg/mL.

WDP formulations using a novel mosquitocidal bacteria, Bacillus thuringiensis subsp. israelensis/tochigiensis (VCRC B-474) - Development and storage stability

A novel mosquito active strain, Bacillus thuringiensis (VCRC B474) sharing the antigens of 2 serotypes, namely israelensis &tochigiensis was characterized by scanning electron microscopy and SDS-PAGE. The spherical and ovoid crystals present in this strain was composed of major polypeptides the size of 28, 65, and 130 kDa respectively. The sporulated cell mass was formulated into water dispersible powder (WDP) formulations with different carrier materials and checked for activity against Culex quinquefasciatus larvae at monthly intervals for up to a year. The formulation containing chalk was the most effective with LC₅₀ values ranging between 0.274-0.523 μg/ml compared to the formulations containing bentonite (0.335-0.775) μg/ml and talc (0.348-0.808 μg/ml). The decline in the activity of these formulations with storage period was as follows: 3 months -14%, 22%, 20% respectively, 6 months - 25%, 35%, 37% respectively, 9 months - 39%, 50%, 47% respectively and 12 months -52%, 43%, 40% respectively. This study demonstrated that wet biomass of bacterial isolates could be simply mixed with carrier materials, dried and used for mosquito larval control without significant loss of activity for up to 6 months at room temperature. Further, this strain of Bacillus thuringiensis var. israelensis/tochigiensis (H14/19) can be a prospective candidate for use in mosquito control programs.

Computational identification and evolutionary analysis of toxins in Mosquitocidal Bacillus thuringiensis strain S2160-1

Mosquitocidal Bacillus thuringiensis (Bt) strain S2160-1 was proposed to be an alternative to Bacillus thuringiensis subsp. israelensis (Bti). Discovering and validating a toxic gene by experimentation was a complex and time-consuming task, which can benefit from high-throughput sequencing analysis. In this research, we predicted and identified toxic proteins in the strain S2160-1 based on the draft whole genome sequence data. Through a local BLASP, 46 putative toxins were identified in S2160-1 genome, by searching against a customized B. thuringiensis toxin proteins database containing 653 protein or peptide sequences retrieved from public accessible resources and PCR/clone results in our laboratory (e value = 1e - 5). These putative toxins consist of 42 to 1216 amino acids. The molecular weights are ranged from 4.86 to 137.28 kDa. The isoelectric point of these candidate toxins varied from 4.3 to 10.06, and 16 out of which had a pH greater than 7.0. The analysis of tertiary structure and PFAM domain showed that 12 potential plasmid toxins may share higher similarity (9/12 QMEAN4 score > 0.3) with known Bt toxins. In addition, functional annotation indicated that these 12 potential toxins were involved in "sporulation resulting in formation of a cellular spore" and "toxin activity". Moreover, multiple alignment and phylogenetic analysis were carried out to elucidate the evolutionary relationship among 101 known crystal or toxin proteins from public database and them with MEGA 6.0. It indicated that PS2160P2_1 and PS2160P2_153 may be potential Cry4-like toxins in Bt S2160-1. This research may lay the foundation for future functional analysis of Bt S2160-1 toxin proteins to reveal their biological roles.

Comparative Genomics of Bacillus thuringiensis Reveals a Path to Specialized Exploitation of Multiple Invertebrate Hosts

Understanding the genetic basis of host shifts is a key genomic question for pathogen and parasite biology. The Bacillus cereus group, which encompasses Bacillus thuringiensis and Bacillus anthracis, contains pathogens that can infect insects, nematodes, and vertebrates. Since the target range of the essential virulence factors (Cry toxins) and many isolates is well known, this group presents a powerful system for investigating how pathogens can diversify and adapt to phylogenetically distant hosts. Specialization to exploit insects occurs at the level of the major clade and is associated with substantial changes in the core genome, and host switching between insect orders has occurred repeatedly within subclades. The transfer of plasmids with linked cry genes may account for much of the adaptation to particular insect orders, and network analysis implies that host specialization has produced strong associations between key toxin genes with similar targets. Analysis of the distribution of plasmid minireplicons shows that plasmids with orf156 and orf157, which carry genes encoding toxins against Lepidoptera or Diptera, were contained only by B. thuringiensis in the specialized insect clade (clade 2), indicating that tight genome/plasmid associations have been important in adaptation to invertebrate hosts. Moreover, the accumulation of multiple virulence factors on transposable elements suggests that cotransfer of diverse virulence factors is advantageous in terms of expanding the insecticidal spectrum, overcoming insect resistance, or through gains in pathogenicity via synergistic interactions between toxins.IMPORTANCE Population genomics have provided many new insights into the formation, evolution, and dynamics of bacterial pathogens of humans and other higher animals, but these pathogens usually have very narrow host ranges. As a pathogen of insects and nematodes, Bacillus thuringiensis, which produces toxins showing toxicity to many orders of insects and other invertebrates, can be used as a model to study the evolution of pathogens with wide host ranges. Phylogenomic analysis revealed that host specialization and switching occur at the level of the major clade and subclade, respectively. A toxin gene co-occurrence network indicates that multiple toxins with similar targets were accumulated by the same cell in the whole species. This accumulation may be one of the strategies that B. thuringiensis has used to fight against host resistance. This kind of formation and evolution of pathogens represents a different path used against multiple invertebrate hosts from that used against higher animals.

Isolation and characterization of a new Bacillus thuringiensis strain with a promising toxicity against Lepidopteran pests

Insecticides derived from Bacillus thuringiensis are gaining worldwide importance as environmentally desirable alternatives to chemicals for the control of pests in public health and agriculture. Isolation and characterization of new strains with higher and broader spectrum of activity is an ever growing field. In the present work, a novel Tunisian B. thuringiensis isolate named BLB459 was characterized and electrophoresis assay showed that among a collection of 200 B. thuringiensis strains, the plasmid profile of BLB459 was distinctive. SmaI-PFGE typing confirmed the uniqueness of the DNA pattern of this strain, compared with BUPM95 and HD1 reference strains. PCR and sequencing assays revealed that BLB459 harbored three cry genes (cry30, cry40 and cry54) corresponding to the obtained molecular sizes in the protein pattern. Interestingly, PCR-RFLP assay demonstrated the originality of the BLB459 cry30-type gene compared to the other published cry30 genes. Insecticidal bioassays showed that BLB459 spore-crystal suspension was highly toxic to both Ephestia kuehniella and Spodoptera littoralis with LC50 values of about 64 (53-75) and 80 (69-91) μg of toxin cm(-2), respectively, comparing with that of the commercial strain HD1 used as reference. Important histopathological effects of BLB459 δ-endotoxins on the two tested larvae midguts were detected, traduced by the vacuolization of the apical cells, the damage of microvilli, and the disruption of epithelial cells. These results proved that BLB459 strain could be of a great interest for lepidopteran biocontrol.

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.