The bacterium, Lysinibacillus sphaericus, as an insect pathogen

Evaluation of a long-lasting microbial larvicide against Culex quinquefasciatus and Aedes aegypti under laboratory and a semi-field trial

BACKGROUND

Microbial larvicides containing both LysiniBacillus sphaericus and Bacillus thuringiensis svar. israelensis (Bti) insecticidal crystals can display advantages for mosquito control. This includes a broader action against larvae that are refractory to the Binary (Bin) toxin from L. sphaericus, as Bin-resistant Culex quinquefasciatus and Aedes aegypti naturally refractory larvae, which often co-habit urban areas of endemic countries for arboviruses. Our principal goal was to assess the toxicity of a combined L. sphaericus/Bti larvicide (Vectomax FG™) to Cx. quinquefasciatus (susceptible CqS and Bin-resistant CqR) and Ae. aegypti (Rocke) and to determine its persistence in the breeding sites with those larvae.

METHODS

The toxicity of a combined L. sphaericus/Bti product (VectoMax FG™) to larvae was performed using bioassays, and persistence was evaluated in simulate field trials carried out under the shade, testing two label concentrations during 12 weeks. A laboratory strain SREC, established with CqS and CqR larvae, was kept during four generations to evaluate the ability of the L. sphaericus/Bti to eliminate resistant larvae.

RESULTS

The L. sphaericus/Bti showed toxicity (mg/L) to larvae from all strains with a decreasing pattern for CqS (LC50 = 0.006, LC90 = 0.030), CqR (LC50 = 0.009, LC90 = 0.069), and Rocke (LC50 = 0.042, LC90 = 0.086). In a simulated field trial, the larvicide showed a persistence of 6 weeks and 8 weeks, controlling larvae from all strains in containers with 100 L of water, using 2 g or 4 g per container (100 L), respectively. The treatment of SREC larvae with L. sphaericus/Bti showed its capacity to eliminate the Bin-resistant individuals using suitable concentrations to target those larvae.

CONCLUSIONS

Our results showed the high efficacy and persistence of the L. sphaericus/Bti larvicide to control Cx. quinquefasciatus and Ae. aegypti that might cohabit breeding sites. These findings demonstrated that such larvicides can be an effective tool for controlling those species in urban areas with a low potential for selecting resistance.

[Deficiency in N-acetylglucosamine transport affects the sporulation process and increases the hemolytic activity of the S-layer protein in Lysinibacillus sphaericus ASB13052]

Lysinibacillus sphaericus is a bacterium that, along with Bacillus thuringiensis var. israelensis, is considered the best biological insecticide for controlling mosquito larvae and an eco-friendly alternative to chemical insecticides. It depends on peptidic molecules such as N-acetylglucosamine to obtain carbon sources and possesses a phosphotransferase system (PTS) for their incorporation. Some strains carry S-layer proteins, whose involvement in metal retention and larvicidal activity against disease-carrying mosquitoes has been demonstrated. Alterations in the amino sugar incorporation system could affect the protein profile and functionality. Strain ASB13052 and the isogenic mutant in the ptsH gene, which is predominant in the PTS signaling pathway, were used in this study. For the first time, the presence of N-glycosylated S-layer proteins was confirmed in both strains, with a variation in their molecular weight pattern depending on the growth phase. In the exponential phase, an S-layer protein greater than 130 kDa was found in the ptsH mutant, which was absent in the wild-type strain. The mutant strain exhibited altered and incomplete low quality sporulation processes. Hemolysis analysis, associated with larvicidal activity, showed that the ptsH mutant has higher lytic efficiency, correlating with the high molecular weight protein. The results allow us to propose the potential effects that arise as a result of the absence of amino sugar transport on hemolytic activity, S-layer isoforms, and the role of N-acetylglucosamine in larvicidal activity.

Biochemical characterisation and production kinetics of high molecular-weight (HMW) putative antibacterial proteins of insect pathogenic Brevibacillus laterosporus isolates

BACKGROUND

Bacterial genomes often encode structures similar to phage capsids (encapsulins) and phage tails which can be induced spontaneously or using genotoxic compounds such as mitomycin C. These high molecular-weight (HMW) putative antibacterial proteins (ABPs) are used against the competitive strains under natural environment. Previously, it was unknown whether these HMW putative ABPs originating from the insect pathogenic Gram-positive, spore-forming bacterium Brevibacillus laterosporus (Bl) isolates (1821L, 1951) are spontaneously induced during the growth and pose a detrimental effect on their own survival. Furthermore, no prior work has been undertaken to determine their biochemical characteristics.

RESULTS

Using a soft agar overlay method with polyethylene glycol precipitation, a narrow spectrum of bioactivity was found from the precipitated lysate of Bl 1951. Electron micrographs of mitomycin C- induced filtrates showed structures similar to phage capsids and contractile tails. Bioactivity assays of cell free supernatants (CFS) extracted during the growth of Bl 1821L and Bl 1951 suggested spontaneous induction of these HMW putative ABPs with an autocidal activity. Sodium dodecyl sulphate-polyacrylamide gel electrophoresis of spontaneously induced putative ABPs showed appearance of ~ 30 kDa and ~ 48 kDa bands of varying intensity across all the time intervals during the bacterial growth except in the initial hours. Statistically, spontaneously induced HMW putative ABPs of Bl 1951 exhibited a significant decrease in the number of viable cells of its producer strain after 18 h of growth in liquid. In addition, a significant change in pH and prominent bioactivity of the CFS of this particular time period was noted. Biochemically, the filtered supernatant derived from either Bl 1821L or Bl 1951 maintained bioactivity over a wide range of pH and temperature.

CONCLUSION

This study reports the spontaneous induction of HMW putative ABPs (bacteriocins) of Bl 1821L and Bl 1951 isolates during the course of growth with potential autocidal activity which is critically important during production as a potential biopesticide. A narrow spectrum of putative antibacterial activity of Bl 1951 precipitate was found. The stability of HMW putative ABPs of Bl 1821L and Bl 1951 over a wide range of pH and temperature can be useful in expanding the potential of this useful bacterium beyond the insecticidal value.

Bacterial biopesticides: Biodiversity, role in pest management and beneficial impact on agricultural and environmental sustainability

Agro-environmental sustainability is based upon the adoption of efficient resources in agro-practices that have a nominal impact on the ecosystem. Insect pests are responsible for causing severe impacts on crop productivity. Wide ranges of agro-chemicals have been employed over the last 50 years to overcome crop yield losses due to insect pests. But better knowledge about the hazards due to chemical pesticides and other pest resistance and resurgence issues necessitates an alternative for pest control. The applications of biological pesticides offer a best alternate that is safe, cost-effective, easy to adoption and successful against various insect pests and pathogens. Like other organisms, insects can get a wide range of diseases from various microbes, such as bacteria, fungi, viruses, protozoa, and nematodes. In order to create agricultural pest management practices that are environmentally beneficial, bacterial entomopathogens are being thoroughly studied. Utilization of bacterial biopesticides has been adopted for the protection of agricultural products. The different types of toxin complexes released by various microorganisms and their mechanisms of action are recapitulated. The present review described the diversity and biocontrol prospective of certain bacteria and summarised the potential of bacterial biopesticides for the management of agricultural pests, insects, and other phytopathogenic microorganisms in agricultural practices.

Comparative genomics reveals insights into the potential of Lysinibacillus irui as a plant growth promoter

Members of the genus Lysinibacillus attract attention for their mosquitocidal, bioremediation, and plant growth-promoting abilities. Despite this interest, comprehensive studies focusing on genomic traits governing plant growth and stress resilience in this genus using whole-genome sequencing are still scarce. Therefore, we sequenced and compared the genomes of three endophytic Lysinibacillus irui strains isolated from Canary Island date palms with the ex-type strain IRB4-01. Overall, the genomes of these strains consist of a circular chromosome with an average size of 4.6 Mb and a GC content of 37.2%. Comparative analysis identified conserved gene clusters within the core genome involved in iron acquisition, phosphate solubilization, indole-3-acetic acid biosynthesis, and volatile compounds. In addition, genome analysis revealed the presence of genes encoding carbohydrate-active enzymes, and proteins that confer resistance to oxidative, osmotic, and salinity stresses. Furthermore, pathways of putative novel bacteriocins were identified in all genomes. This illustrates possible common plant growth-promoting traits shared among all strains of L. irui. Our findings highlight a rich repertoire of genes associated with plant lifestyles, suggesting significant potential for developing inoculants to enhance plant growth and resilience. This study is the first to provide insights into the overall genomic signatures and mechanisms of plant growth promotion and biocontrol in the genus Lysinibacillus. KEY POINTS: • Pioneer study in elucidating plant growth promoting in L. irui through comparative genomics. • Genome mining identified biosynthetic pathways of putative novel bacteriocins. • Future research directions to develop L. irui-based biofertilizers for sustainable agriculture.

In vitro acaricidal activity of several natural products against ibex-derived Sarcoptes scabiei

In this study we analysed the effect of the temperature, diverse strains of Bacillus thuringiensis, Lysinibacillus sphaericus and nanoformulations with essential plant oils (EONP) on the survival of Sarcoptes scabiei mites derived from naturally-infested Iberian ibex (Capra pyrenaica). In general, mites maintained at 12ºC survived more than those maintained at 35ºC (40.7 hr and 31.2 hr, respectively). Mites with no treatment survived 27.6 h on average. Mites treated with B. thuringiensis serovar. konkukian and geranium EONP showed significant reduction in their survival. Despite the fact that these agents seem to be promising candidates for controlling sarcoptic mange in the field, further research is still needed to get stable, efficient and eco-friendly acaricides.

The Perpetual Vector Mosquito Threat and Its Eco-Friendly Nemeses

Mosquitoes are the most notorious arthropod vectors of viral and parasitic diseases for which approximately half the world's population, ~4,000,000,000, is at risk. Integrated pest management programs (IPMPs) have achieved some success in mitigating the regional transmission and persistence of these diseases. However, as many vector-borne diseases remain pervasive, it is obvious that IPMP successes have not been absolute in eradicating the threat imposed by mosquitoes. Moreover, the expanding mosquito geographic ranges caused by factors related to climate change and globalization (travel, trade, and migration), and the evolution of resistance to synthetic pesticides, present ongoing challenges to reducing or eliminating the local and global burden of these diseases, especially in economically and medically disadvantaged societies. Abatement strategies include the control of vector populations with synthetic pesticides and eco-friendly technologies. These "green" technologies include SIT, IIT, RIDL, CRISPR/Cas9 gene drive, and biological control that specifically targets the aquatic larval stages of mosquitoes. Regarding the latter, the most effective continues to be the widespread use of Lysinibacillus sphaericus (Ls) and Bacillus thuringiensis subsp. israelensis (Bti). Here, we present a review of the health issues elicited by vector mosquitoes, control strategies, and lastly, focus on the biology of Ls and Bti, with an emphasis on the latter, to which no resistance has been observed in the field.

Culex quinquefasciatus membrane-bound alkaline phosphatase is a putative receptor for Lysinibacillus sphaericus Tpp49Aa1 toxin

The binary toxin Cry48Aa1/Tpp49Aa1 produced by Lysinibacillus sphaericus exhibits potent toxicity against Culicidae larvae. Both Cry48Aa1 and Tpp49Aa1 toxins are crucial for binding to the toxin receptor in Culex quinquefasciatus larvae, albeit with different binding sites. Previous studies have identified Glu71, a membrane-bound α-glucosidase, as a putative binding protein for the Cry48Aa1 toxin, involved in the Cry48Aa1/Tpp49Aa1 toxicity. In this study, we employed pulldown assays to identify a group of Tpp49Aa1-binding proteins from C. quinquefasciatus solubilized midgut brush-border membrane proteins (BBMFs). RNA interference assays revealed that the silencing of an alkaline phosphatase gene (referred to as ALP1263) in C. quinquefasciatus resulted in a significant reduction in larval mortality upon exposure to Cry48Aa1/Tpp49Aa1 toxin in vivo. Furthermore, the ALP1263 protein exhibited specific and high-affinity binding to the Tpp49Aa1 toxin, with a dissociation constant (Kd) of approximately 57.3 nM. The dot blot analysis demonstrated that Tpp49Aa1 C-terminal region was essential for its interaction with the ALP1263 protein. In summary, our findings establish ALP1263 as a functional receptor for Tpp49Aa1 and emphasize its role in the toxicity of Cry48Aa1/Tpp49Aa1.

Culex quinquefasciatus Resistant to the Binary Toxin from Lysinibacillus sphaericus Displays a Consistent Downregulation of Pantetheinase Transcripts

Culex quinquefasciatus resistance to the binary (Bin) toxin, the major larvicidal component from Lysinibacillus sphaericus, is associated with mutations in the cqm1 gene, encoding the Bin-toxin receptor. Downregulation of the cqm1 transcript was found in the transcriptome of larvae resistant to the L. sphaericus IAB59 strain, which produces both the Bin toxin and a second binary toxin, Cry48Aa/Cry49Aa. Here, we investigated the transcription profiles of two other mosquito colonies having Bin resistance only. These confirmed the cqm1 downregulation and identified transcripts encoding the enzyme pantetheinase as the most downregulated mRNAs in both resistant colonies. Further quantification of these transcripts reinforced their strong downregulation in Bin-resistant larvae. Multiple genes were found encoding this enzyme in Cx. quinquefasciatus and a recombinant pantetheinase was then expressed in Escherichia coli and Sf9 cells, with its presence assessed in the midgut brush border membrane of susceptible larvae. The pantetheinase was expressed as a ~70 kDa protein, potentially membrane-bound, which does not seem to be significantly targeted by glycosylation. This is the first pantetheinase characterization in mosquitoes, and its remarkable downregulation might reflect features impacted by co-selection with the Bin-resistant phenotype or potential roles in the Bin-toxin mode of action that deserve to be investigated.

Random Mutational Analysis Targeting Residue K155 within the Transmembrane β-Hairpin of the Mosquitocidal Mpp46Ab Toxin

Mpp46Ab is a mosquito-larvicidal pore-forming toxin derived from Bacillus thuringiensis TK-E6. Pore formation is believed to be a central mode of Mpp46Ab action, and the cation selectivity of the channel pores, in particular, is closely related to its mosquito-larvicidal activity. In the present study, we constructed a mutant library in which residue K155 within the transmembrane β-hairpin was randomly replaced with other amino acid residues. Upon mutagenesis and following primary screening using Culex pipiens mosquito larvae, we obtained 15 mutants in addition to the wild-type toxin. Bioassays using purified proteins revealed that two mutants, K155E and K155I, exhibited toxicity significantly higher than that of the wild-type toxin. Although increased cation selectivity was previously reported for K155E channel pores, we demonstrated in the present study that the cation selectivity of K155I channel pores was also significantly increased. Considering the characteristics of the amino acids, the charge of residue 155 may not directly affect the cation selectivity of Mpp46Ab channel pores. Replacement of K155 with glutamic acid or isoleucine may induce a similar conformational change in the region associated with the ion selectivity of the Mpp46Ab channel pores. Mutagenesis targeting the transmembrane β-hairpin may be an effective strategy for enhancing the ion permeability of the channel pores and the resulting mosquito-larvicidal activity of Mpp46Ab.

An Alkaline Foregut Protects Herbivores from Latex in Forage, but Increases Their Susceptibility to Bt Endotoxin

About 10% of angiosperms, an estimated 20,000 species, produce latex from ubiquitous isoprene precursors. Latex, an aqueous suspension of rubber particles and other compounds, functions as an antifeedant and herbivory deterrent. It is soluble in neutral to alkaline pH, and coagulates in acidic environments. Here, I propose that foregut-fermenting herbivores such as ruminants, kangaroos, sloths, insect larvae, and tadpoles have adapted to latex in forage with the evolution of alkaline anterior digestive chamber(s). However, they consequently become susceptible to the action of Bacillus thuringiensis (Bt) δ-endotoxin and related bioinsecticides which are activated in alkaline environments. By contrast, hindgut-fermenting herbivores, such as horses and rabbits, have acidic anterior digestive chambers, in which latex coagulates and may cause gut blockage, but in which Bt is not activated. The latex-adapted foregut herbivore vs. latex-maladapted hindgut herbivore hypothesis developed in this paper has implications for hindgut-fermenting livestock and zoo animals which may be provided with latex-containing forage that is detrimental to their gut health. Further, ruminants and herbivorous tadpoles with alkaline anterior chambers are at risk of damage by the supposedly "environmentally friendly" Bt bioinsecticide, which is widely disseminated or engineered into crops which may enter animal feed streams.

First Case Report of Peritoneal Dialysis-associated Peritonitis Caused by Lysinibacillus sphaericus

We herein report a case of peritoneal dialysis-associated peritonitis caused by Lysinibacillus sphaericus in a 40s-year-old patient. Treatment was initiated with intermittent intraperitoneal cefazolin and ceftazidime. Later, both peritoneal dialysate and blood cultures detected L. sphaericus, so the antibiotic was changed to ampicillin (ABPC). The patient was treated with a combination of intraperitoneal intermittent and intravenous ABPC for 7 days, followed by 14 days of amoxicillin. The patient experienced no adverse events and no recurrence for 30 days. The patient had four dogs, and the infection was deemed likely to have been caused by environmental contamination and inadequate catheter replacement.

A Culex quinquefasciatus strain resistant to the binary toxin from Lysinibacillus sphaericus displays altered enzyme activities and energy reserves

BACKGROUND

The resistance of a Culex quinquefasciatus strain to the binary (Bin) larvicidal toxin from Lysinibacillus sphaericus is due to the lack of expression of the toxin's receptors, the membrane-bound Cqm1 α-glucosidases. A previous transcriptomic profile of the resistant larvae showed differentially expressed genes coding Cqm1, lipases, proteases and other genes involved in lipid and carbohydrate metabolism. This study aimed to investigate the metabolic features of Bin-resistant individuals by comparing the activity of some enzymes, energy reserves, fertility and fecundity to a susceptible strain.

METHODS

The activity of specific enzymes was recorded in midgut samples from resistant and susceptible larvae. The amount of lipids and reducing sugars was determined for larvae and adults from both strains. Additionally, the fecundity and fertility parameters of these strains under control and stress conditions were examined.

RESULTS

Enzyme assays showed that the esterase activities in the midgut of resistant larvae were significantly lower than susceptible ones using acetyl-, butyryl- and heptanoyl-methylumbelliferyl esthers as substrates. The α-glucosidase activity was also reduced in resistant larvae using sucrose and a synthetic substrate. No difference in protease activities as trypsins, chymotrypsins and aminopeptidases was detected between resistant and susceptible larvae. In larval and adult stages, the resistant strain showed an altered profile of energy reserves characterized by significantly reduced levels of lipids and a greater amount of reducing sugars. The fertility and fecundity of females were similar for both strains, indicating that those changes in energy reserves did not affect these reproductive parameters.

CONCLUSIONS

Our dataset showed that Bin-resistant insects display differential metabolic features co-selected with the phenotype of resistance that can potentially have effects on mosquito fitness, in particular, due to the reduced lipid accumulation.

Isolated and identified pathogenic bacteria from black soldier fly larvae with "soft rot" reared in mass production facilities and its incidence characteristics

The black soldier fly larvae (BSFL) can transform organic waste into high-end proteins, lipids, chitin, biodiesel, and melanin at an industrial scale. But scaling up of its production capacity has also posed health risks to the insect itself. In this investigation, larval "soft rot" which is occurring in mass production facilities that cause larval developmental inhibition and a certain degree of death was reported. Responsible pathogen GX6 was isolated from BSFL with "soft rot" and identified to be Paenibacillus thiaminolyticus. No obvious impact on larval growth was observed when treated with GX6 spores, whereas mortality of 6-day-old BSFL increased up to 29.33% ± 2.05% when GX6 vegetative cells (1 × 10⁶ cfu/g) were inoculated into the medium. Moreover, higher temperature further enhanced the BSFL mortality and suppressed larval development, but increasing substrate moisture showed the opposite effect. The middle intestine of infected larvae became swollen and transparent after dissection and examination. Transmission electron microscopy (TEM) observation indicated that GX6 had destroyed the peritrophic matrix and intestinal microvilli and damaged epithelial cells of larval gut. Furthermore, 16S rRNA gene sequencing analysis of intestinal samples revealed that gut microflora composition was significantly altered by GX6 infection as well. It can be noticed that Dysgonomonas, Morganella, Myroides, and Providencia bacteria became more numerous in the intestines of GX6-infected BSFL as compared to controls. This study will lay foundations for efficient control of "soft rot" and promote healthy development of the BSFL industry to contribute to organic waste management and circular economy.

Lysinibacillus spp.: an IAA-producing endospore forming-bacteria that promotes plant growth

Lysinibacillus is a bacterial genus that has generated recent interest for its biotechnological potential in agriculture. Strains belonging to this group are recognized for their mosquitocidal and bioremediation activity. However, in recent years some reports indicate its importance as plant growth promoting rhizobacteria (PGPR). This research sought to provide evidence of the PGP activity of Lysinibacillus spp. and the role of the indole-3-acetic acid (IAA) production associated with this activity. Twelve Lysinibacillus spp. strains were evaluated under greenhouse conditions, six of which increased the biomass and root architecture of corn plants. In most cases, growth stimulation was evident at 10⁸ CFU/mL inoculum concentration. All strains produced IAA with high variation between them (20-70 µg/mL). The bioinformatic identification of predicted genes associated with IAA production allowed the detection of the indole pyruvic acid pathway to synthesize IAA in all strains; additionally, genes for a tryptamine pathway were detected in two strains. Extracellular filtrates from all strain's cultures increased the corn coleoptile length in an IAA-similar concentration pattern, which demonstrates the filtrates had an auxin-like effect on plant tissue. Five of the six strains that previously showed PGPR activity in corn also promoted the growth of Arabidopsis thaliana (col 0). These strains induced changes in root architecture of Arabidopsis mutant plants (aux1-7/axr4-2), the partial reversion of mutant phenotype indicated the role of IAA on plant growth. This work provided solid evidence of the association of Lysinibacillus spp. IAA production with their PGP activity, which constitutes a new approach for this genus. These elements contribute to the biotechnological exploration of this bacterial genus for agricultural biotechnology.

Chromobacterium Biopesticide Exposure Does Not Select for Resistance in Aedes Mosquitoes

Developing effective tools to control mosquito populations is essential for reducing the incidence of diseases like malaria and dengue. Biopesticides of microbial origin are a rich, underexplored source of mosquitocidal compounds. We previously developed a biopesticide from the bacterium Chromobacterium sp. Panama that rapidly kills vector mosquito larvae, including Aedes aegypti and Anopheles gambiae. Here, we demonstrate that two independent Ae. aegypti colonies exposed to a sublethal dose of that biopesticide over consecutive generations persistently exhibited high mortality and developmental delays, indicating that resistance did not develop during the study period. Critically, the descendants of biopesticide-exposed mosquitoes experienced decreased longevity and did not display increased susceptibility to dengue virus or decreased susceptibility to common chemical insecticides. Through RNA sequencing, we observed no link between biopesticide exposure and the increased activity of xenobiotic metabolism and detoxification genes typically associated with insecticide resistance. These findings indicate that the Chromobacterium biopesticide is an exciting, emerging mosquito control tool. IMPORTANCE Vector control is an essential part of mitigating diseases caused by pathogens that mosquitoes spread. Modern vector control is highly reliant on using synthetic insecticides to eliminate mosquito populations before they can cause disease. However, many of these populations have become resistant to commonly used insecticides. There is a strong need to explore alternative vector control strategies that aim to mitigate disease burden. Biopesticides, insecticides of biological origin, can have unique mosquitocidal activities, meaning they can effectively kill mosquitoes that are already resistant to other insecticides. We previously developed a highly effective mosquito biopesticide from the bacterium Chromobacterium sp. Csp_P. Here, we investigate whether exposure to a sublethal dose of this Csp_P biopesticide over 9 to 10 generations causes resistance to arise in Aedes aegypti mosquitoes. We find no evidence of resistance at the physiological or molecular levels, confirming that the Csp_P biopesticide is a highly promising new tool for controlling mosquito populations.

Engineering BinB Pore-Forming Toxin for Selective Killing of Breast Cancer Cells

Breast cancer is one of the most common cancers in women worldwide. Conventional cancer chemotherapy always has adverse side effects on the patient's healthy tissues. Consequently, combining pore-forming toxins with cell-targeting peptides (CTPs) is a promising anticancer strategy for selectively destroying cancer cells. Here, we aim to improve the target specificity of the BinB toxin produced from Lysinibacillus sphaericus (Ls) by fusing a luteinizing hormone-releasing hormone (LHRH) peptide to its pore-forming domain (BinB_C) to target MCF-7 breast cancer cells as opposed to human fibroblast cells (Hs68). The results showed that LHRH-BinB_C inhibited MCF-7 cell proliferation in a dose-dependent manner while leaving Hs68 cells unaffected. BinB_C, at any concentration tested, did not affect the proliferation of MCF-7 or Hs68 cells. In addition, the LHRH-BinB_C toxin caused the efflux of the cytoplasmic enzyme lactate dehydrogenase (LDH), demonstrating the efficacy of the LHRH peptide in directing the BinB_C toxin to damage the plasma membranes of MCF-7 cancer cells. LHRH-BinB_C also caused MCF-7 cell apoptosis by activating caspase-8. In addition, LHRH-BinB_C was predominantly observed on the cell surface of MCF-7 and Hs68 cells, without colocalization with mitochondria. Overall, our findings suggest that LHRH-BinB_C could be investigated further as a potential cancer therapeutic agent.

Interspecies Horizontal Transfer and Specific Integration of the Mosquitocidal Toxin-Encoding Plasmid pTAND672-2 from Bacillus thuringiensis subsp. israelensis to Lysinibacillus sphaericus

pTAND672-2, a 144-kb resident plasmid of Bacillus thuringiensis serovar israelensis strain TAND672, was sequenced and characterized. This extrachromosomal element carries mosquitocidal toxin-, conjugation-, and recombinase-encoding genes, together with a putative arbitrium system, a genetic module recently discovered in temperate phages controlling lysogeny-lysis transition and in mobile genetic elements (MGEs) where its function remains clarified. Using conjugation experiments, pTAND672-2 is shown to be a novel integrative and conjugative element (ICE), which can horizontally transfer from B. thuringiensis serovar israelensis to Lysinibacillus sphaericus, another mosquitocidal bacterium, where it integrates into the chromosome. Its integration and circularization are reversible and involve a single-cross recombination between 33-bp specific sites, attB in the chromosome of L. sphaericus and attP in pTAND672-2. CDS143, coding for the putative tyrosine integrase Int143 distantly related to site-specific tyrosine Xer recombinases and phage integrases, can mediate the integration of pTAND672-2 to attB. The B. thuringiensis mosquito-killing genes carried by pTAND672-2 are efficiently transcribed and expressed in L. sphaericus, displaying a slight increased toxicity in this bacterium against Aedes albopictus larvae. The occurrence of pTAND672-2-like plasmids within the Bacillus cereus group was also explored and indicated that they all share a similar genetic backbone with diverse plasmid sizes, ranging from 58 to 225 kb. Interestingly, among them, the pEFR-4-4 plasmid of Bacillus paranthracis EFR-4 and p5 of B. thuringiensis BT-59 also display conjugative capability; moreover, like pTAND672-2 displays a chimeric structure between the pCH_133-e- and pBtoxis-like plasmids, pBTHD789-3 also appears to be mosaic of two plasmids. IMPORTANCE Horizontal transfer of mobile genetic elements carrying mosquitocidal toxin genes may play a driving role in the diversity of mosquitocidal bacteria. Here, the 144-kb mosquitocidal toxin-encoding plasmid pTAND672-2 is the first verified integrative and conjugative element (ICE) identified in Bacillus thuringiensis serovar israelensis. The key tyrosine integrase Int143, involved in the specific integration, is distantly related to other tyrosine recombinases. The study also reports the occurrence and potential interspecies transmission of pTAND672-2-like plasmids with varied sizes in B. thuringiensis, Bacillus paranthracis, and Bacillus wiedmannii isolates belonging to the Bacillus cereus group. This study is important for further understanding the evolution and ecology of mosquitocidal bacteria, as well as for providing new direction for the genetic engineering of biopesticides in the control of disease-transmitting mosquitoes.

Pelgipeptins, a Nonribosomal Lipopeptide Family, Show Larvicidal Activity against Vectors Transmitting Viruses

Aedes aegypti and Culex quinquefasciatus are vectors of numerous diseases of worldwide public importance, such as arboviruses and filariasis. The main strategy for controlling these vectors is the use of chemicals, which can induce the appearance of resistant insects. The use of Bacillus thuringiensis (Bt) and Lysinibacillus sphaericus (Ls) with larvicidal activity against arboviral-transmitting insects has been successful in many studies. In contrast, the use and knowledge of peptides with insecticidal activity are so far scarce. In this work, 25 peptides and 5 strains of each bacterial species were prospected individually or together regarding their insecticidal activity. Initially, in vitro assays of cellular cytotoxicity of the peptides against SF21 cells of Spodoptera frugiperda were performed. The peptides Polybia-MPII and pelgipeptin caused 69 and 60% of cell mortality, respectively, at the concentration of 10 μM. Thus, they were evaluated in vivo against second-stage larvae of the two Culicidae. However, in the in vivo bioassays, only pelgipeptin showed larvicidal mortality against both larvae (LC₅₀ 6.40 μM against A. aegypti, and LC₅₀ 1.22 μM against C. quinquefasciatus). The toxin-producing bacterial strain that showed the lowest LC₅₀ against A. aegypti was Bt S8 (LC₅₀ = 0.71 ng/mL) and against C. quinquefasciatus, it was Ls S260 (LC₅₀ = 2.32 ng/mL). So, the synergistic activity between the association of the bacterial toxins and pelgipeptin was evaluated. A synergic effect of pelgipeptin was observed with Ls strain S260 against C. quinquefasciatus. Our results demonstrate the possibility of synergistic or individual use of both biologically active larvicides against C. quinquefasciatus and A. aegypti.

Lysinibacilli: A Biological Factories Intended for Bio-Insecticidal, Bio-Control, and Bioremediation Activities

Microbes are ubiquitous in the biosphere, and their therapeutic and ecological potential is not much more explored and still needs to be explored more. The bacilli are a heterogeneous group of Gram-negative and Gram-positive bacteria. Lysinibacillus are dominantly found as motile, spore-forming, Gram-positive bacilli belonging to phylum Firmicutes and the family Bacillaceae. Lysinibacillus species initially came into light due to their insecticidal and larvicidal properties. Bacillus thuringiensis, a well-known insecticidal Lysinibacillus, can control many insect vectors, including a malarial vector and another, a Plasmodium vector that transmits infectious microbes in humans. Now its potential in the environment as a piece of green machinery for remediation of heavy metal is used. Moreover, some species of Lysinibacillus have antimicrobial potential due to the bacteriocin, peptide antibiotics, and other therapeutic molecules. Thus, this review will explore the biological disease control abilities, food preservative, therapeutic, plant growth-promoting, bioremediation, and entomopathogenic potentials of the genus Lysinibacillus.

Beyond the snapshot: identification of the timeless, enduring indicator microbiome informing soil fertility and crop production in alkaline soils

BACKGROUND

Microorganisms are known to be important drivers of biogeochemical cycling in soil and hence could act as a proxy informing on soil conditions in ecosystems. Identifying microbiomes indicative for soil fertility and crop production is important for the development of the next generation of sustainable agriculture. Earlier researches based on one-time sampling have revealed various indicator microbiomes for distinct agroecosystems and agricultural practices as well as their importance in supporting sustainable productivity. However, these microbiomes were based on a mere snapshot of a dynamic microbial community which is subject to significant changes over time. Currently true indicator microbiomes based on long-term, multi-annual monitoring are not available.

RESULTS

Here, using samples from a continuous 20-year field study encompassing seven fertilization strategies, we identified the indicator microbiomes ecophysiologically informing on soil fertility and crop production in the main agricultural production base in China. Among a total of 29,184 phylotypes in 588 samples, we retrieved a streamlined consortium including 2% of phylotypes that were ubiquitously present in alkaline soils while contributing up to half of the whole community; many of them were associated with carbon and nutrient cycling. Furthermore, these phylotypes formed two opposite microbiomes. One indicator microbiome dominated by Bacillus asahii, characterized by specific functional traits related to organic matter decomposition, was mainly observed in organic farming and closely associated with higher soil fertility and crop production. The counter microbiome, characterized by known nitrifiers (e.g., Nitrosospira multiformis) as well as plant pathogens (e.g., Bacillus anthracis) was observed in nutrient-deficit chemical fertilizations. Both microbiomes are expected to be valuable indictors in informing crop yield and soil fertility, regulated by agricultural management.

CONCLUSIONS

Our findings based on this more than 2-decade long field study demonstrate the exciting potential of employing microorganisms and maximizing their functions in future agroecosystems. Our results report a "most-wanted" or "most-unwanted" list of microbial phylotypes that are ready candidates to guide the development of sustainable agriculture in alkaline soils.

BPPRC database: a web-based tool to access and analyse bacterial pesticidal proteins

Pesticidal proteins derived from the bacterium Bacillus thuringiensis, have provided the bases for a diverse array of pest management tools ranging from natural products used in organic agriculture, to modern biotechnological approaches. With advances in genome sequencing technologies and protein structure determination, an increasing number of pesticidal proteins from myriad bacterial species have been identified. The Bacterial Pesticidal Protein Resource Center (BPPRC) has been established to provide informational and analytical resources on the wide range of pesticidal proteins derived from bacteria that have potential utility for arthropod management. In association with a revised nomenclature for these proteins, BPPRC contains a database that allows users to browse and download sequences. Users can search the database for the best matches to sequences of interest and can incorporate their own sequences into basic informatic analyses. These analyses include the ability to draw and export guide trees from either whole protein sequences or, in the case of the three-domain Cry proteins, from individual domains. The associated website also provides a portal for users to submit protein sequences for naming. The BPPRC provides a single authoritative source of information to which all stakeholders can be referred including academics, government regulatory bodies and research and development personnel in the industrial sector. The database provides information on more than 1060 pesticidal proteins derived from 13 species of bacteria, including insecticidal activities for a subset of these proteins.

Database URL: www.bpprc.org and www.bpprc-db.org/

Mosquito-larvicidal Binary (BinA/B) proteins for mosquito control programs —advancements, challenges, and possibilities

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Binary (BinAB) toxin is primarily responsible for the larvicidal action of the WHO recognized mosquito-larvicidal bacterium Lysinibacillus sphaericus.

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BinAB is a single receptor-specific toxin, active against larvae of Culex and Anopheles, but not Aedes aegypti.

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The target receptor in Culex is Cqm1 protein, a GPI-anchored amylomaltase located apically in the lipid-rafts of the larval-midgut epithelium.

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Interaction of the toxin components with the receptor is critical for the larvicidal activity of the toxin.

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Evidences support the pore formation model for BinAB toxin internalization and the role of toxin-glycan interactions in the endoplasmic reticulum in mediating larval death.

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Targeted R&D efforts are required to maintain the sustainability and improve efficacy of the eco-friendly BinAB proteins for efficient mosquito control interventions.

The increasing global burden of mosquito-borne diseases require targeted, environmentally friendly, and sustainable approaches for effective vector control without endangering the non-target beneficial insect population. Biological interventions such as biopesticides, Wolbachia-mediated biological controls, or sterile insect techniques are used worldwide. Here we review Binary or BinAB toxin—the mosquito-larvicidal component of WHO-recognized Lysinibacillus sphaericus bacterium employed in mosquito control programs. Binary (BinAB) toxin is primarily responsible for the larvicidal effect of the bacterium. BinAB is a single-receptor-specific toxin and is effective against larvae of Culex and Anopheles, but not against Aedes aegypti. The receptor in Culex, the Cqm1 protein, has been extensively studied. It is a GPI-anchored amylomaltase and is located apically in the lipid rafts of the larval-midgut epithelium. The interaction of the toxin components with the receptor is crucial for the mosquito larvicidal activity of the BinAB toxin. Here we extend support for the pore formation model of BinAB toxin internalization and the role of toxin-glycan interactions in the endoplasmic reticulum in mediating larval death. BinAB is phylogenetically safe for humans, as Cqm1-like protein is not expected in the human proteome. This review aims to initiate targeted R&D efforts, such as applying fusion technologies (chimera of BinA, chemical modification of BinA), for efficient mosquito control interventions. In addition, the review also examines other areas such as bioremediation and cancer therapeutics, in which L. sphaericus is proving useful and showing potential for further development.

Lysinibacillus xylanilyticus Strain GIC41 as a Potential Plant Biostimulant

To identify Lysinibacillus strains with the potential to function as plant biostimulants, we screened 10 previously isolated Lysinibacillus strains from the rhizosphere and soil for their plant growth-promoting (PGP) effects. In vitro tests showed that all strains produced indole-3-acetic acid. In primary screening, the PGP effects of these strains were assessed on spinach seedlings grown on Jiffy-7 pellets; strains GIC31, GIC41, and GIC51 markedly promoted shoot growth. In secondary screening, the PGP efficacies of these three strains were examined using spinach seedlings grown in pots under controlled conditions. Only GIC41 exerted consistent and significant PGP effects; therefore, it was selected for subsequent experiments. The results of 6-week glasshouse experiments revealed that GIC41 markedly increased shoot dry weight by ca. 12–49% over that of the control. The impact of fertilization levels on the PGP efficacy of GIC41 was investigated using pot experiments. The application of a specific level of fertilizer was required for the induction of sufficient PGP effects by this strain. The phylogenetic ana­lysis based on the 16S rDNA sequence identified GIC41 as L. xylanilyticus. Collectively, these results show the potential of strain GIC41 to function as a plant biostimulant.

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.

Bacterial Toxins Active against Mosquitoes: Mode of Action and Resistance

Larvicides based on the bacteria Bacillus thuringiensis svar. israelensis (Bti) and Lysinibacillus sphaericus are effective and environmentally safe compounds for the control of dipteran insects of medical importance. They produce crystals that display specific and potent insecticidal activity against larvae. Bti crystals are composed of multiple protoxins: three from the three-domain Cry type family, which bind to different cell receptors in the midgut, and one cytolytic (Cyt1Aa) protoxin that can insert itself into the cell membrane and act as surrogate receptor of the Cry toxins. Together, those toxins display a complex mode of action that shows a low risk of resistance selection. L. sphaericus crystals contain one major binary toxin that display an outstanding persistence in field conditions, which is superior to Bti. However, the action of the Bin toxin based on its interaction with a single receptor is vulnerable for resistance selection in insects. In this review we present the most recent data on the mode of action and synergism of these toxins, resistance issues, and examples of their use worldwide. Data reported in recent years improved our understanding of the mechanism of action of these toxins, showed that their combined use can enhance their activity and counteract resistance, and reinforced their relevance for mosquito control programs in the future years.

Prospects and Pitfalls: Next-Generation Tools to Control Mosquito-Transmitted Disease

Mosquito-transmitted diseases, including malaria and dengue, are a major threat to human health around the globe, affecting millions each year. A diverse array of next-generation tools has been designed to eliminate mosquito populations or to replace them with mosquitoes that are less capable of transmitting key pathogens. Many of these new approaches have been built on recent advances in CRISPR/Cas9-based genome editing. These initiatives have driven the development of pathogen-resistant lines, new genetics-based sexing methods, and new methods of driving desirable genetic traits into mosquito populations. Many other emerging tools involve microorganisms, including two strategies involving Wolbachia that are achieving great success in the field. At the same time, other mosquito-associated bacteria, fungi, and even viruses represent untapped sources of new mosquitocidal or antipathogen compounds. Although there are still hurdles to be overcome, the prospect that such approaches will reduce the impact of these diseases is highly encouraging.

Proteomics-based identification of orchid-associated bacteria colonizing the Epipactis albensis, E. helleborine and E. purpurata (Orchidaceae, Neottieae)

Using proteomics-based identification by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS), we conducted the first analysis of the composition of endophytic bacteria isolated from different parts of selected Epipactis species, i.e. the buds, the inflorescences and the central part of the shoots, as well as the rhizomes. We identified aerobic and anaerobic bacteria, including such taxa as Bacillus spp., Clostridium spp., Pseudomonas spp. and Stenotrophomonas spp., which may be considered as promoting plant growth. Because most of the indicated bacteria genera belong to spore-producing taxa (spores allow bacterial symbionts to survive adverse conditions), we suggest that these bacteria species contribute to the adaptation of orchids to the environment. We found clear differences in the microbiome between investigated closely related taxa, i.e., Epipactis albensis, E. helleborine, E. purpurata and E. purpurata f. chlorophylla. Some of the analysed orchid species, i.e. E. albensis and E. purpurata co-occur in habitats, and their bacterial microbiomes differ from each other.

Production of Lysinibacillus sphaericus Mosquitocidal Protein Mtx2 from Bacillus subtilis as a Secretory Protein

BACKGROUND

Mtx2 is a mosquitocidal toxin produced during the vegetative growth of Lysinibacillus sphaericus. The protein shows synergism with other toxins against mosquito larvae; hence it could be used in mosquito control formulations. The protein expression system is needed for Mtx2 development as a biocontrol agent.

OBJECTIVE

The objective of the study was to set up a Bacillus subtilis system to produce Mtx2 as a secreted protein since the protein contains a putative signal peptide.

METHODS

Initially, four different promoters (P43, Pspac, PxylA, and PyxiE) were compared for their strength using GFP as a reporter in B. subtilis. Subsequently, six different signal peptides (SacB, Epr, AmyE, AprE, LipA, and Vip3A)were tested in conjunction with the selected promoter and mtx2 to evaluate levels of Mtx2 secreted by B. subtilis WB800, an extracellular protease-deficient strain.

RESULTS

The promoter PyxiE showed the highest GFP intensity and was selected for further study. Mtx2 was successfully produced as a secreted protein from signal peptides LipA and AmyE, and exhibited larvicidal activity against Aedesaegypti.

CONCLUSION

B. subtilis was successfully developed as a host for the production of secreted Mtx2 and the protein retained its larvicidal activity. Although the Mtx2 production level still needs improvement, the constructed plasmids could be used to produce other soluble proteins.

Entomopathogenic Fungi and Bacteria in a Veterinary Perspective

Simple Summary

Several fungal species are well suited to control arthropods, being able to cause epizootic infection among them and most of them infect their host by direct penetration through the arthropod’s tegument. Most of organisms are related to the biological control of crop pests, but, more recently, have been applied to combat some livestock ectoparasites. Among the entomopathogenic bacteria, Bacillus thuringiensis, innocuous for humans, animals, and plants and isolated from different environments, showed the most relevant activity against arthropods. Its entomopathogenic property is related to the production of highly biodegradable proteins. Entomopathogenic fungi and bacteria are usually employed against agricultural pests, and some studies have focused on their use to control animal arthropods. However, risks of infections in animals and humans are possible; thus, further studies about their activity are necessary.

Abstract

The present study aimed to review the papers dealing with the biological activity of fungi and bacteria against some mites and ticks of veterinary interest. In particular, the attention was turned to the research regarding acarid species, Dermanyssus gallinae and Psoroptes sp., which are the cause of severe threat in farm animals and, regarding ticks, also pets. Their impact on animal and human health has been stressed, examining the weaknesses and strengths of conventional treatments. Bacillus thuringiensis, Beauveria bassiana and Metarhizium anisopliae are the most widely employed agents. Their activities have been reviewed, considering the feasibility of an in-field application and the effectiveness of the administration alone or combined with conventional and alternative drugs is reported.

Coordinated binding of a two-component insecticidal protein from Alcaligenes faecalis to western corn rootworm midgut tissue

AfIP-1A/1B is a two-component insecticidal protein identified from the soil bacterium Alcaligenes faecalis that has high activity against western corn rootworm (WCR; Diabrotica virgifera virgifera LeConte). Previous results revealed that AfIP-1A/1B is cross-resistant to the binary protein from Bacillus thuringiensis (Bt), Cry34Ab1/Cry35Ab1 (also known as Gpp34Ab1/Tpp35Ab1; Crickmore et al., 2020), which was attributed to shared binding sites in WCR gut tissue (Yalpani et al., 2017). To better understand the interaction of AfIP-1A/1B with its receptor, we have systematically evaluated the binding of these proteins with WCR brush border membrane vesicles (BBMVs). Our findings show that AfIP-1A binds directly to BBMVs, while AfIP-1B does not; AfIP-1B binding only occurred in the presence of AfIP-1A which was accompanied by the presence of stable, high molecular weight oligomers of AfIP-1B observed on denaturing protein gels. Additionally, we show that AfIP-1A/1B forms pores in artificial lipid membranes. Finally, binding of AfIP-1A/1B was found to be reduced in BBMVs from Cry34Ab1/Cry35Ab1-resistant WCR where Cry34Ab1/Cry35Ab1 binding was also reduced. The reduced binding of both proteins is consistent with recognition of a shared receptor that has been altered in the resistant strain. The coordination of AfIP-1B binding by AfIP-1A, the similar structures between AfIP-1A and Cry34Ab1, along with their shared binding sites and cross-resistance, suggest a similar role for AfIP1A and Cry34Ab1 in receptor recognition and docking site for their cognate partners, AfIP-1B and Cry35Ab1, respectively.

Horizontal transfer of large plasmid with type IV secretion system and mosquitocidal genomic island with excision and integration capabilities in Lysinibacillus sphaericus

We identified a ~30-kb genomic island (named GI8) carrying the binary toxin gene operon binA/binB on both the chromosome and large pBsph plasmid in the mosquitocidal Lysinibacillus sphaericus C3-41 strain. We found that GI8 is related to the occurrence of binA/binB within L. sphaericus and displays excision and integration capability by recognizing the attB region, which consists of a 2-nt target site (AT) flanked by an 11-nt imperfect inverted repeat. pBsph and two pBsph-like plasmids (p2362 and p1593) were found to carry a type IV secretion system (T4SS) and displayed transmissibility within a narrow host range specific to L. sphaericus. GI8 can be co-transferred with pBsph as a composite element by integration into its attB site, then excised from pBsph and re-integrated into the chromosomal attB site in the new host. The potential hosts of GI8, regardless of whether they are toxic or non-toxic to mosquito larvae, share good collinearity at the chromosomal level. Data indicated that the appearance of the mosquitocidal L. sphaericus lineage was driven by horizontal transfer of the T4SS-type conjugative plasmid and GI8 with excision and specific integration capability.

Characterization of the major antifungal extrolite from rice endophyte Lysinibacillus sphaericus against Rhizoctonia solani

Sheath blight of rice caused by Rhizoctonia solani is regarded as one of the most widely distributed diseases of rice, and is one of the major production constraints for rice in India and most rice-growing countries of Asia. Biological control of plant diseases using antagonistic bacteria is now considered as a promising alternative to the use of hazardous chemical fungicides or bactericides. Several bacterial endophytes have been reported to support growth and improve the health of the plants and therefore, may be important as biocontrol agents. In the present study, putative antifungal metabolites were extracted from rice foliage endophyte Lysinibacillus sphaericus KJ872548 by solvent extraction methods and purified using HPTLC techniques. Separated bands were subjected to assess the in vitro antagonistic activity toward rice sheath blight pathogen Rhizoctonia solani using a dual culture method. Partially purified active fraction B2 obtained from HPTLC analysis showed the highest percentage of inhibition (76.9%). GC MS and FTIR analyses of B2 revealed the compound as1, 2-Benzenedicarboxylic acid butyl 2-Ethylhexyl ester, a strong antifungal volatile organic compound. Light microscopic analysis of the fungal mycelium from the dual culture plate of both culture filtrate and 1, 2-Benzenedicarboxylic acid butyl 2-Ethylhexyl ester disclosed strong mycolytic activity as evident by mycelial distractions and shrinkage. This is the first report on antifungal production by endophytic Lysinibacillus sphaericus against R. solani, the rice sheath blight pathogen. The findings of this study biologically prospect the endophyte L. sphaericus as an inexpensive broad spectrum bioagent for eco-friendly, economic and sustainable agriculture.

Cry75Aa (Mpp75Aa) Insecticidal Proteins for Controlling the Western Corn Rootworm, Diabrotica virgifera virgifera, (Coleoptera: Chrysomelidae), Isolated from the Insect Pathogenic Bacteria Brevibacillus laterosporus

This study describes three closely related proteins, cloned from Brevibacillus laterosporus strains, that are lethal upon feeding to Diabrotica virgifera virgifera LeConte, the western corn rootworm (WCR). Mpp75Aa1, Mpp75Aa2 and Mpp75Aa3 were toxic to WCR larvae when fed purified protein. Transgenic plants expressing each mMpp75Aa protein were protected from feeding damage and showed significant reduction in adult emergence from infested plants by both susceptible and Cry3Bb1 and Cry34Ab1/Cry35Ab1-resistant WCR. These results demonstrate that proteins from B. laterosporus are as efficacious as the well-known Bacillus thuringiensis (Bt) insecticidal proteins in controlling major insect pests such as WCR. The deployment of transgenic maize expressing mMpp75Aa along with other active molecules lacking cross-resistance have the potential to be a useful tool for control of WCR populations resistant to current Bt traits.IMPORTANCE Insects feeding on roots of crops can damage the plant roots resulting in yield loss due to poor water and nutrient uptake and plant lodging. In maize the western corn rootworm (WCR) can cause severe damage to the roots resulting in significant economic loss for farmers. Genetically modified (GM) expressing Bacillus thuringiensis (Bt) insect control proteins, has provided a solution for control of these pests. In recent years populations of WCR resistant to the Bt proteins in commercial GM maize have emerged. There is a need to develop new insecticidal traits for the control of WCR populations resistant to current commercial traits. New proteins with commercial level efficacy on WCR from sources other than Bt are becoming more critical. The Mpp75Aa proteins, from B. laterosporus, when expressed in maize, are efficacious against the resistant populations of WCR and have the potential to provide solutions for control of resistant WCR.

Culex quinquefasciatus carrying Wolbachia is less susceptible to entomopathogenic bacteria

In an attempt to evaluate the susceptibility of the mosquito Culex quinquefasciatus to bacterial agents, a population naturally infected with a Wolbachia pipientis wPipSJ native strain was tested against the action of three bacterial mosquitocides, Bacillus thuringiensis subsp. israelensis, Bacillus wiedmannii biovar thuringiensis and Lysinibacillus sphaericus. Tests were carried out on mosquito larvae with and without Wolbachia (controls). Cx. quinquefasciatus naturally infected with the native wPipSJ strain proved to be more resistant to the pathogenic action of the three mosquitocidal bacterial strains. Additionally, wPipSJ was fully characterised using metagenome-assembled genomics, PCR-RFLP (PCR-Restriction Fragment Length Polymorphism) and MLST (MultiLocus Sequence Typing) analyses. This Wolbachia strain wPipSJ belongs to haplotype I, group wPip-III and supergroup B, clustering with other mosquito wPip strains, such as wPip PEL, wPip JHB, wPip Mol, and wAlbB; showing the southernmost distribution in America. The cytoplasmic incompatibility phenotype of this strain was revealed via crosses between wildtype (Wolbachia⁺) and antibiotic treated mosquito populations. The results of the tests with the bacterial agents suggest that Cx. quinquefasciatus naturally infected with wPipSJ is less susceptible to the pathogenic action of mosquitocidal bacterial strains when compared with the antibiotic-treated mosquito isoline, and is more susceptible to B. thuringiensis subsp. israelensis than to the other two mosquitocidal agents.

Microbial dynamics in rearing trials of Hermetia illucens larvae fed coffee silverskin and microalgae

In the present study, Hermetia illucens larvae were reared on a main rearing substrate composed of a coffee roasting byproduct (coffee silverskin, Cs) enriched with microalgae (Schizochytrium limacinum or Isochrysis galbana) at various substitution levels. The microbial diversity of the rearing substrates, larvae, and frass (excrement from the larvae mixed with the substrate residue) were studied by the combination of microbial culturing on various growth media and metataxonomic analysis (Illumina sequencing). High counts of total mesophilic aerobes, bacterial spores, presumptive lactic acid bacteria, coagulase-positive cocci, and eumycetes were detected. Enterobacteriaceae counts were low in the rearing diets, whereas higher counts of this microbial family were observed in the larvae and frass. The microbiota of the rearing substrates was characterized by the presence of lactic acid bacteria, including the genera Lactobacillus, Leuconostoc and Weissella. The microbiota of the H. illucens larvae fed Cs was characterized by the dominance of Paenibacillus. H. illucens fed diets containing I. galbana were characterized by the presence of Enterococcus, Lysinibacillus, Morganella, and Paenibacillus, depending on the algae inclusion level, while H. illucens fed diets containing S. limacinum were characterized by high relative abundances of Brevundimonas, Enterococcus, Paracoccus, and Paenibacillus, depending on the algae inclusion level. Brevundimonas and Alcaligenes dominated in the frass from larvae fed I. galbana; the predominance of Brevundimonas was also observed in the frass from larvae fed Schyzochitrium-enriched diets. Based on the results of the present study, an effect of algae nutrient bioactive substances (e.g. polysaccharides, high-unsaturated fatty acids, taurine, carotenoids) on the relative abundance of some of the bacterial taxa detected in larvae may be hypothesized, thus opening new intriguing perspectives for the control of the entomopathogenic species and foodborne human pathogens potentially occurring in edible insects. Further studies are needed to support this hypothesis. Finally, new information on the microbial diversity occurring in insect frass was also obtained.

Potential for Bacillus thuringiensis and Other Bacterial Toxins as Biological Control Agents to Combat Dipteran Pests of Medical and Agronomic Importance

The control of dipteran pests is highly relevant to humans due to their involvement in the transmission of serious diseases including malaria, dengue fever, Chikungunya, yellow fever, zika, and filariasis; as well as their agronomic impact on numerous crops. Many bacteria are able to produce proteins that are active against insect species. These bacteria include Bacillus thuringiensis, the most widely-studied pesticidal bacterium, which synthesizes proteins that accumulate in crystals with insecticidal properties and which has been widely used in the biological control of insects from different orders, including Lepidoptera, Coleoptera, and Diptera. In this review, we summarize all the bacterial proteins, from B. thuringiensis and other entomopathogenic bacteria, which have described insecticidal activity against dipteran pests, including species of medical and agronomic importance.

Assessment of the Synergic Effect between Lysinibacillus sphaericus S-Layer Protein and Glyphosate in the Lethality of the Invasive Arboviral Vector Aedes albopictus

Glyphosate and glyphosate-based herbicides are among the most used chemicals in plant pest control. Both glyphosate and its main by-product Aminomethylphosphonic Acid (AMPA) are highly environmentally persistent and, through several processes (including surface runoff and bioaccumulation), affect species beyond their intended targets, especially in aquatic ecosystems. Aedes albopictus is a novel invasive arboviral vector in Colombia and has spread to much of the national territory in recent years. Strains of the bacterium Lysinibacillus sphaericus have shown the ability to degrade glyphosate into environmentally inert compounds, in addition to having great larvicidal efficiency in different mosquito species through the production of several proteins, including the surface layer (S-Layer) protein. The S-Layer is a bacterial structure consisting of glycoprotein monomers, and its functions are thought to include bacterial interactions, protection from the outside medium and biological control. The study assessed the entomopathogenic activity of L. sphaericus S-Layer protein on Ae. albopictus larvae, and the effects that glyphosate and its by-products have in this process. To that end, bioassays were performed to compare the larval mortality between different treatments with and without S-Layer, glyphosate, and glyphosate derivates. Comparisons were made through Analysis of variance (ANOVA) and Tukey's Honestly Significant Difference (HSD) analyses. Significant differences were found in larval mortality in the treatments, and larval mortality was greater when the S-Layer protein was present, though glyphosate field-doses (1.69 g/L) alone had a notable toxicity as well. An apparent synergic effect on the mortality of larval Ae. albopictus when exposed to mixtures containing 1500 ppm of the S-Layer protein, glyphosate, and/or glyphosate derivates was found. Further studies are needed for the in-depth understanding of this mechanism and its consequences on aquatic ecosystems.

Culturing-Enriched Metabarcoding Analysis of the Oryctes rhinoceros Gut Microbiome

Simple Summary

The coconut rhinoceros beetle is a pest of palm trees, which may have symbiotic gut microbes that help it digest its food. These microbes may produce enzymes like cellulase, which have uses in human industry. If the microbes are essential for the beetle’s survival, then finding ways to attack the microbes could help fight the pest. We sampled microbes from the guts of larval beetles collected in coconut trees in southern Taiwan, and identified the microbes both by culturing and with molecular biology methods. We found several species of bacteria and a yeast, Candida xylanolytica, with potential digestive functions for the beetle. Some of these microbes had been reported in these beetles before while others are new. Broader surveys of the beetle microbiome are needed to determine whether or not they have a conserved microbiome.

Abstract

Wood-feeding insects should have a source of enzymes like cellulases to digest their food. These enzymes can be produced by the insect, or by microbes living in the wood and/or inside the insect gut. The coconut rhinoceros beetle, Oryctes rhinoceros, is a pest whose digestive microbes are of considerable interest. This study describes the compartments of the O. rhinoceros gut and compares their microbiomes using culturing-enriched metabarcoding. Beetle larvae were collected from a coconut grove in southern Taiwan. Gut contents from the midgut and hindgut were plated on nutrient agar and selective carboxymethylcellulose agar plates. DNA was extracted from gut and fat body samples and 16S rDNA metabarcoding performed to identify unculturable bacteria. Cellulase activity tests were performed on gut fluids and microbe isolates. The midgut and hindgut both showed cellulolytic activity. Bacillus cereus, Citrobacter koseri, and the cellulolytic fungus Candida xylanilytica were cultured from both gut sections in most larvae. Metabarcoding did not find Bacillus cereus, and found that either Citrobacter koseri or Paracoccus sp. were the dominant gut microbes in any given larva. No significant differences were found between midgut and hindgut microbiomes. Bacillus cereus and Citrobacter koseri are common animal gut microbes frequently found in Oryctes rhinoceros studies while Candida xylanilytica and the uncultured Paracoccus sp. had not been identified in this insect before. Some or all of these may well have digestive functions for the beetle, and are most likely acquired from the diet, meaning they may be transient commensalists rather than obligate mutualists. Broader collection efforts and tests with antibiotics will resolve ambiguities in the beetle–microbe interactions.

Insights into the Current Trends in the Utilization of Bacteria for Microbially Induced Calcium Carbonate Precipitation

Nowadays, microbially induced calcium carbonate precipitation (MICP) has received great attention for its potential in construction and geotechnical applications. This technique has been used in biocementation of sand, consolidation of soil, production of self-healing concrete or mortar, and removal of heavy metal ions from water. The products of MICP often have enhanced strength, durability, and self-healing ability. Utilization of the MICP technique can also increase sustainability, especially in the construction industry where a huge portion of the materials used is not sustainable. The presence of bacteria is essential for MICP to occur. Bacteria promote the conversion of suitable compounds into carbonate ions, change the microenvironment to favor precipitation of calcium carbonate, and act as precipitation sites for calcium carbonate crystals. Many bacteria have been discovered and tested for MICP potential. This paper reviews the bacteria used for MICP in some of the most recent studies. Bacteria that can cause MICP include ureolytic bacteria, non-ureolytic bacteria, cyanobacteria, nitrate reducing bacteria, and sulfate reducing bacteria. The most studied bacterium for MICP over the years is Sporosarcina pasteurii. Other bacteria from Bacillus species are also frequently investigated. Several factors that affect MICP performance are bacterial strain, bacterial concentration, nutrient concentration, calcium source concentration, addition of other substances, and methods to distribute bacteria. Several suggestions for future studies such as CO₂ sequestration through MICP, cost reduction by using plant or animal wastes as media, and genetic modification of bacteria to enhance MICP have been put forward.

Genomics and Proteomics Analyses Revealed Novel Candidate Pesticidal Proteins in a Lepidopteran-Toxic Bacillus thuringiensis Strain

Discovery and identification of novel insecticidal proteins in Bacillus thuringiensis (Bt) strains are of crucial importance for efficient biological control of pests and better management of insect resistance. In this study, the Bt strain KhF, toxic for Plodia interpunctella and Grapholita molesta larvae, underwent genomics and proteomics analyses to achieve a better understanding of the bases of its pathogenicity. The whole-genome sequencing results revealed that the KhF strain contained nine coding sequences with homologies to Bt insecticidal genes. The lepidopteran toxic mixture of spores and crystals of this Bt strain was subjected to liquid chromatography and tandem mass spectrometry (LC-MS/MS) to assess the protein composition. The results of the proteomic analyses, combined with the toxin gene sequences, revealed that two of the main components of the crystals were two new candidate pesticidal proteins, named KhFA and KhFB. These proteins showed a similarity lower than 36% to the other known Bt toxins. The phylogenetic analysis showed that the KhFA and KhFB grouped with the newly denominated Xpp and Mpp (former ETX/Mtx) pesticidal protein groups, respectively. Altogether, this study has led to the discovery of two novel candidate pesticidal toxins in the lepidopteran toxic KhF strain.

Genetically modified entomopathogenic bacteria, recent developments, benefits and impacts: A review

Entomopathogenic bacteria (EPBs), insect pathogens that produce pest-specific toxins, are environmentally-friendly alternatives to chemical insecticides. However, the most important problem with EPBs application is their limited field stability. Moreover, environmental factors such as solar radiation, leaf temperature, and vapor pressure can affect the pathogenicity of these pathogens and their toxins. Scientists have conducted intensive research to overcome such problems. Genetic engineering has great potential for the development of new engineered entomopathogens with more resistance to adverse environmental factors. Genetically modified entomopathogenic bacteria (GM-EPBs) have many advantages over wild EPBs, such as higher pathogenicity, lower spraying requirements and longer-term persistence. Genetic manipulations have been mostly applied to members of the bacterial genera Bacillus, Lysinibacillus, Pseudomonas, Serratia, Photorhabdus and Xenorhabdus. Although many researchers have found that GM-EPBs can be used safely as plant protection bioproducts, limited attention has been paid to their potential ecological impacts. The main concerns about GM-EPBs and their products are their potential unintended effects on beneficial insects (predators, parasitoids, pollinators, etc.) and rhizospheric bacteria. This review address recent update on the significant role of GM-EPBs in biological control, examining them through different perspectives in an attempt to generate critical discussion and aid in the understanding of their potential ecological impacts.

The Anopheles coluzzii microbiome and its interaction with the intracellular parasite Wolbachia

Wolbachia, an endosymbiotic alpha-proteobacterium commonly found in insects, can inhibit the transmission of human pathogens by mosquitoes. Biocontrol programs are underway using Aedes aegypti mosquitoes trans-infected with a non-natural Wolbachia strain to reduce dengue virus transmission. Less is known about the impact of Wolbachia on the biology and vectorial capacity of Anopheles mosquitoes, the vectors of malaria parasites. A naturally occurring strain of Wolbachia, wAnga, infects populations of the major malaria vectors Anopheles gambiae and Anopheles coluzzii in Burkina Faso. Previous studies found wAnga infection was negatively correlated with Plasmodium infection in the mosquito and wAnga influenced mosquito egg-laying behavior. Here, we investigate wAnga in natural populations of An. coluzzii and its interactions with other resident microbiota using targeted 16S sequencing. Though we find no major differences in microbiota composition associated with wAnga infection, we do find several taxa that correlate with the presence or absence of wAnga in female mosquitoes following oviposition, with the caveat that we could not rule out batch effects due to the unanticipated impact of wAnga on oviposition timing. These data suggest wAnga may influence or interact with the Anopheles microbiota, which may contribute to the impact of wAnga on Anopheles biology and vectorial capacity.

In vitro analysis of the anticancer activity of Lysinibacillus sphaericus binary toxin in human cancer cell lines

Binary or Bin toxin produced by Lysinibacillus sphaericus is composed of BinA (42 kDa) and BinB (51 kDa) subunits. These work together to exert maximal toxicity against mosquito larvae via pore formation and induction of apoptosis. The C-terminal domains in both subunits are homologous to those of aerolysin-type β pore-forming toxins, including parasporin-2 (PS2). The latter is one of the Bacillus thuringiensis toxins that exhibits specific cytotoxicity against human cancer cells. The present study investigates the possible anticancer activity of Bin toxin using PS2 as a control. We demonstrate that treatment with a high concentration of trypsin-activated Bin inhibits cell proliferation in human cancer cells A549, Caco-2, HepG2, HK-1 and KKU-M055. In the most susceptible cells, HK-1, Bin toxin exposure led to morphological alterations, decreased migration, decreased adhesion activity and apoptosis induction. Although these effects necessitated high concentrations, they suggest that Bin toxin may be optimized as a novel potential cancer-therapeutic agent.

Identification of bacterial endospores and targeted detection of foodborne viruses in industrially reared insects for food

With edible insects being increasingly produced, food safety authorities have called for the determination of microbiological challenges posed to human health. Here, we find that the bacterial endospore fraction in industrially reared mealworm and cricket samples is largely comprised of Bacillus cereus group members that can pose insect or human health risks. Hepatitis A virus, hepatitis E virus and norovirus genogroup II were not detected in the sample collection, indicating a low food safety risk from these viral pathogens.

Liposome-Based Study Provides Insight into Cellular Internalization Mechanism of Mosquito-Larvicidal BinAB Toxin

Glycosylphosphatidylinositols (GPIs) anchored proteins are commonly localized onto lipid rafts. These extracellular proteins participate in a variety of cellular functions, including as receptors for viruses and toxins. Intracellular trafficking of World Health Organization recognized mosquito-larvicidal BinAB toxin is mediated via GPI-anchored Cqm1 receptor protein in Culex mosquitoes. We confirmed conformational change in Cqm1 dimer on interaction with BinA/BinB proteins by dynamic light scattering, modelling of hydrodynamic parameters using the atomic structures, and synchrotron Small Angle solution X-ray scattering (SAXS). A reliable model of the receptor-BinB complex was also constructed from joint SAXS/SANS refinement. We confirmed electrostatic interactions of the Cqm1 ectodomain with lipid rafts reconstituted in model membranes and report receptor-dependent impairment of model liposomes by BinA/B proteins. Liposomal disruption was toxin concentration-dependent as monitored by the release of encapsulated carboxyfluorescein dye. Interestingly, BinA alone, without BinB, showed efficient efflux of the fluorescent dye in agreement with the reported high larvicidal activity of BinA variants. The study provides insight into BinA/B toxin internalization mechanism in the membrane model that is toxin internalization is mediated via receptor-dependent pore formation mechanism. It also suggests a tangible and environmentally safe strategy for control of mosquito population.

Computational analysis identifies druggable mutations in human rBAT mediated Cystinuria

Culex quinquefasciatus Cqm1 protein acts as the receptor for Lysinibacillus sphaericus mosquito-larvicidal binary (BinAB) toxin that is used worldwide for mosquito control. We found amino acid transporter protein, rBAT, as phylogenetically closest Cqm1 homolog in humans. The present study reveals large evolutionary distance between Cqm1 and rBAT, and rBAT ectodomain lacks the sequence motif which serves as binding-site for the BinAB toxin. Thus, BinAB toxin can be expected to remain safe for humans. rBAT (heavy subunit; SLC3A1) and catalytic b^0,+AT (light subunit; SLC7A9), linked by single disulfide bond, mediate renal reabsorption of cystine and dibasic amino acids in Na⁺ independent manner. Mutations in rBAT cause type I Cystinuria disease which shows global prevalence, and rBAT can be thought as an important pharmacological target. However, 3D structures of rBAT and b^0,+AT, the two components of b^0,+ heteromeric amino acid transporter systems, are not available. We constructed a reliable homology model of rBAT using Cqm1 coordinates and that of transmembrane b^0,+AT subunit using LAT1 coordinates. Mapping of pathogenic mutations onto rBAT ectodomain revealed their scattered distribution throughout the rBAT protein. Further, our computational simulations-based scoring of several known deleterious mutations of rBAT revealed that mutations those do not compromise the protein fold and stability, are localized on the same face of the molecule. These residues are expected to interact with the b^0,+AT transporter. The present study thus identifies druggable sites on rBAT that could be targeted for the treatment of type I Cystinuria.Communicated by Ramaswamy H. Sarma.