Cloning, functional characterization, and mode of action of a novel insecticidal pore-forming toxin, sphaericolysin, produced by Bacillus sphaericus

Divergent venom effectors correlate with ecological niche in neuropteran predators

Neuropteran larvae are fierce predators that use venom to attack and feed on arthropod prey. Neuropterans have adapted to diverse and sometimes extreme habitats, suggesting their venom may have evolved accordingly, but the ecology and evolution of venom deployment in different families is poorly understood. We applied spatial transcriptomics, proteomics, morphological analysis, and bioassays to investigate the venom systems in the antlion Euroleon nostras and the lacewing Chrysoperla carnea, which occupy distinct niches. Although the venom system morphology was similar in both species, we observed remarkable differences at the molecular level. E. nostras produces particularly complex venom secreted from three different glands, indicating functional compartmentalization. Furthermore, E. nostras venom and digestive tissues were devoid of bacteria, strongly suggesting that all venom proteins are of insect origin rather than the products of bacterial symbionts. We identified several toxins exclusive to E. nostras venom, including phospholipase A2 and several undescribed proteins with no homologs in the C. carnea genome. The compositional differences have significant ecological implications because only antlion venom conferred insecticidal activity, indicating its use for the immobilization of large prey. Our results indicate that molecular venom evolution plays a role in the adaptation of antlions to their unique ecological niche.

Transcriptome analysis revealed that short-term stress in Blattella germanica to β-cypermethrin can reshape the phenotype of resistance adaptation

Previous studies on insect resistance have primarily focused on resistance monitoring and the molecular mechanisms involved, while overlooking the process of phenotype formation induced by insecticide stress. In this study, we compared the expression profiles of a beta-cypermethrin (β-CYP) resistant strain (R) and a susceptible strain (S) of Blattella germanica after β-CYP induction using transcriptome sequencing. In the short-term stress experiment, we identified a total of 792 and 622 differentially expressed genes (DEGs) in the S and R strains. Additionally, 893 DEGs were identified in the long-term adaptation experiment. To validate the RNA-Seq data, we performed qRT-PCR on eleven selected DEGs, and the results were consistent with the transcriptome sequencing data. These DEGs exhibited down-regulation in the short-term stress group and up-regulation in the long-term adaptation group. Among the validated DEGs, CUO8 and Cyp4g19 were identified and subjected to knockdown using RNA interference. Subsequent insecticide bioassays revealed that the mortality rate of cockroaches treated with β-CYP increased by 69.3% and 66.7% after silencing the CUO8 and Cyp4g19 genes (P<0.05). Furthermore, the silencing of CUO8 resulted in a significant thinning of the cuticle by 59.3% and 53.4% (P<0.05), as observed through transmission electron microscopy and eosin staining, in the S and R strains, respectively. Overall, our findings demonstrate that the phenotypic plasticity in response to short-term stress can reshape the adaptive mechanisms of genetic variation during prolonged exposure to insecticides. And the identified resistance-related genes, CUO8 and Cyp4g19, could serve as potential targets for controlling these pest populations.

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.

Draft Genome Sequence of Bacillus wiedmannii Biovar thuringiensis ZZQ-138, Isolated from a Saline Lake

Ecologically sound approaches to control mosquitoes like Anopheles stephensi, which are obligatory vectors for malaria transmission, are urgently needed because of increasing insecticide resistance. Bacteria from Bacillus are important resources. Here, we report the whole-genome sequence of Bacillus wiedmannii biovar thuringiensis ZZQ-138, which was isolated from sediment from a saline lake.

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.

Synergistic effect of Lysinibacillus sphaericus and glyphosate on temephos-resistant larvae of Aedes aegypti

BACKGROUND

Glyphosate-based herbicides are one of the most commonly used compounds to control perennial weeds around the world. This compound is very persistent in the environment and tends to filter into aquatic ecosystems, affecting non-target species such as mosquito larvae. Aedes aegypti mosquitoes are vectors of multiple arboviruses such as dengue and Zika. Glyphosate can be degraded into non-harmful environmental compounds by Lysinibacillus sphaericus, a spore forming bacterium which can also kill Ae. aegypti larvae. In this study, we assessed the effect of glyphosate concentrations, typically used in Colombia, on the entomopathogenic activity of L. sphaericus against Ae. aegypti larvae.

METHODS

Bioassays and toxicity curves were performed to compare the larval mortality between different treatments with and without bacteria and glyphosate (Roundup 747®). Larvae were exposed to both bacteria and glyphosate by adding the compound on chloride-free water. Comparisons were made using both probit regression and ANOVA analysis.

RESULTS

ANOVA showed a significant difference in larval mortality when adding glyphosate and L. sphaericus at the same time. Thus, a positive synergic effect on larval mortality was found when L. sphaericus and glyphosate were mixed. According to probit analysis, median lethal dose (LD50) for bacterial mixture was of 106.23 UFC/ml and for glyphosate was 2.34 g/l.

CONCLUSIONS

A positive synergic effect on the mortality of larval Ae. aegypti when exposed to L. sphaericus mixture and glyphosate was found. Molecular studies focusing on the toxin production of L. sphaericus are required to understand more about this synergistic effect.

Repertoire of the Bacillus thuringiensis Virulence Factors Unrelated to Major Classes of Protein Toxins and Its Role in Specificity of Host-Pathogen Interactions

Bacillus thuringiensis (Bt) is a Gram-positive soil bacteria that infects invertebrates, predominantly of Arthropoda phylum. Due to its immense host range Bt has become a leading producer of biopesticides applied both in biotechnology and agriculture. Cytotoxic effect of Bt, as well as its host specificity, are commonly attributed either to proteinaceous crystal parasporal toxins (Cry and Cyt) produced by bacteria in a stationary phase or to soluble toxins of Vip and Sip families secreted by vegetative cells. At the same time, numerous non-toxin virulence factors of Bt have been discovered, including metalloproteases, chitinases, aminopolyol antibiotics and nucleotide-mimicking moieties. These agents act at each stage of the B. thuringiensis invasion and contribute to cytotoxic properties of Bt strains enhancing toxin activity, ensuring host immune response evasion and participating in extracellular matrix degeneration. In this review we attempt to classify Bt virulence factors unrelated to major groups of protein toxins and discuss their putative role in the establishment of Bt specificity to various groups of insects.

Cophylogenetic analysis suggests cospeciation between the Scorpion Mycoplasma Clade symbionts and their hosts

Scorpions are predator arachnids of ancient origin and worldwide distribution. Two scorpion species, Vaejovis smithi and Centruroides limpidus, were found to harbor two different Mollicutes phylotypes: a Scorpion Mycoplasma Clade (SMC) and Scorpion Group 1 (SG1). Here we investigated, using a targeted gene sequencing strategy, whether these Mollicutes were present in 23 scorpion morphospecies belonging to the Vaejovidae, Carboctonidae, Euscorpiidae, Diplocentridae, and Buthidae families. Our results revealed that SMC is found in a species-specific association with Vaejovidae and Buthidae, whereas SG1 is uniquely found in Vaejovidae. SMC and SG1 co-occur only in Vaejovis smithi where 43% of the individuals host both phylotypes. A phylogenetic analysis of Mollicutes 16S rRNA showed that SMC and SG1 constitute well-delineated phylotypes. Additionally, we found that SMC and scorpion phylogenies are significantly congruent, supporting the observation that a cospeciation process may have occurred. This study highlights the phylogenetic diversity of the scorpion associated Mollicutes through different species revealing a possible cospeciation pattern.

A genome-scale metabolic reconstruction of Lysinibacillus sphaericus unveils unexploited biotechnological potentials

The toxic lineage (TL) of Lysinibacillus sphaericus has been extensively studied because of its potential biotechnological applications in biocontrol of mosquitoes and bioremediation of toxic metals. We previously proposed that L. sphaericus TL should be considered as a novel species based on a comparative genomic analysis. In the current work, we constructed the first manually curated metabolic reconstruction for this species on the basis of the available genomes. We elucidated the central metabolism of the proposed species and, beyond confirming the reported experimental evidence with genomic a support, we found insights to propose novel applications and traits to be considered in further studies. The strains belonging to this lineage exhibit a broad repertory of genes encoding insecticidal factors, some of them remain uncharacterized. These strains exhibit other unexploited biotechnological important traits, such as lactonases (quorum quenching), toxic metal resistance, and potential for aromatic compound degradation. In summary, this study provides a guideline for further research aimed to implement this organism in biocontrol and bioremediation. Similarly, we highlighted the unanswered questions to be responded in order to gain a deeper understanding of the L. sphaericus TL biology.

An in-depth characterization of the entomopathogenic strain Bacillus pumilus 15.1 reveals that it produces inclusion bodies similar to the parasporal crystals of Bacillus thuringiensis

In the present work, the local isolate Bacillus pumilus 15.1 has been morphologically and biochemically characterized in order to gain a better understanding of this novel entomopathogenic strain active against Ceratitis capitata. This strain could represent an interesting biothechnological tool for the control of this pest. Here, we report on its nutrient preferences, extracellular enzyme production, motility mechanism, biofilm production, antibiotic suceptibility, natural resistance to chemical and physical insults, and morphology of the vegetative cells and spores. The pathogen was found to be β-hemolytic and susceptible to penicillin, ampicillin, chloramphenicol, gentamicin, kanamycin, rifampicin, tetracycline, and streptomycin. We also report a series of biocide, thermal, and UV treatments that reduce the viability of B. pumilus 15.1 by several orders of magnitude. Heat and chemical treatments kill at least 99.9 % of vegetative cells, but spores were much more resistant. Bleach was the only chemical that was able to completely eliminate B. pumilus 15.1 spores. Compared to the B. subtilis 168 spores, B. pumilus 15.1 spores were between 2.67 and 350 times more resistant to UV radiation while the vegetative cells of B. pumilus 15.1 were almost up to 3 orders of magnitude more resistant than the model strain. We performed electron microscopy for morphological characterization, and we observed geometric structures resembling the parasporal crystal inclusions synthesized by Bacillus thuringiensis. Some of the results obtained here such as the parasporal inclusion bodies produced by B. pumilus 15.1 could potentially represent virulence factors of this novel and potentially interesting strain.

Toxins Secreted by Bacillus Isolated from Lung Adenocarcinomas Favor the Penetration of Toxic Substances

The aim was to explore the eventual role of bacteria in the induction of lung cancer by smoking habits. Viable bacteria closely related to the genus Bacillus were detected at high frequencies in lung-cancer biopsies. Similar, if not identical, microbes were isolated from cigarettes and in smog. Bacteria present in cigarettes could be transferred to a physiological solution via a "smoker" device that mimicked their potential transfer during smoking those bacteria produce exotoxins able to open transmembrane pores. These channels can be used as a way to penetrate cells of benzopyrenes and other toxic substances present in tobacco products. We hypothesize that Bacillaceae present in tobacco play a key role in the development of lung cancer.

Draft Genome Sequence of the Entomopathogenic Bacterium Bacillus pumilus 15.1, a Strain Highly Toxic to the Mediterranean Fruit Fly Ceratitis capitata

We present the draft whole-genome sequence of the entomopathogenic Bacillus pumilus 15.1 strain that consists of 3,795,691 bp and 3,776 predicted protein-coding genes. This genome sequence provides the basis for understanding the potential mechanism behind the toxicity and virulence of B. pumilus 15.1 against the Mediterranean fruit fly.

Genome sequence and description of the mosquitocidal and heavy metal tolerant strain Lysinibacillus sphaericus CBAM5

Lysinibacillus sphaericus CBAM5, was isolated from subsurface soil of oil well explorations in the Easter Planes of Colombia. This strain has potential in bioremediation of heavy-metal polluted environments and biological control of Culex quinquefasciatus. According to the phylogenetic analysis of 16S rRNA gene sequences, the strain CBAM5 was assigned to the Lysinibacillus sphaericus taxonomic group 1 that comprises mosquito pathogenic strains. After a combination assembly-integration, alignment and gap-filling steps, we propose a 4,610,292 bp chromosomal scaffold. The whole genome (consisting of 5,146,656 bp long, 60 contigs and 5,209 predicted-coding sequences) revealed strong functional and syntenial similarities to the L. sphaericus C3-41 genome. Mosquitocidal (Mtx), binary (Bin) toxins, cereolysin O, and heavy metal resistance clusters from nik, ars, czc, mnt, ter, cop, cad, and znu operons were identified.

Bacillus thuringiensis toxins: an overview of their biocidal activity

Bacillus thuringiensis (Bt) is a Gram positive, spore-forming bacterium that synthesizes parasporal crystalline inclusions containing Cry and Cyt proteins, some of which are toxic against a wide range of insect orders, nematodes and human-cancer cells. These toxins have been successfully used as bioinsecticides against caterpillars, beetles, and flies, including mosquitoes and blackflies. Bt also synthesizes insecticidal proteins during the vegetative growth phase, which are subsequently secreted into the growth medium. These proteins are commonly known as vegetative insecticidal proteins (Vips) and hold insecticidal activity against lepidopteran, coleopteran and some homopteran pests. A less well characterized secretory protein with no amino acid similarity to Vip proteins has shown insecticidal activity against coleopteran pests and is termed Sip (secreted insecticidal protein). Bin-like and ETX_MTX2-family proteins (Pfam PF03318), which share amino acid similarities with mosquitocidal binary (Bin) and Mtx2 toxins, respectively, from Lysinibacillus sphaericus, are also produced by some Bt strains. In addition, vast numbers of Bt isolates naturally present in the soil and the phylloplane also synthesize crystal proteins whose biological activity is still unknown. In this review, we provide an updated overview of the known active Bt toxins to date and discuss their activities.

Common Virulence Factors and Tissue Targets of Entomopathogenic Bacteria for Biological Control of Lepidopteran Pests

This review focuses on common insecticidal virulence factors from entomopathogenic bacteria with special emphasis on two insect pathogenic bacteria Photorhabdus (Proteobacteria: Enterobacteriaceae) and Bacillus (Firmicutes: Bacillaceae). Insect pathogenic bacteria of diverse taxonomic groups and phylogenetic origin have been shown to have striking similarities in the virulence factors they produce. It has been suggested that the detection of phage elements surrounding toxin genes, horizontal and lateral gene transfer events, and plasmid shuffling occurrences may be some of the reasons that virulence factor genes have so many analogs throughout the bacterial kingdom. Comparison of virulence factors of Photorhabdus, and Bacillus, two bacteria with dissimilar life styles opens the possibility of re-examining newly discovered toxins for novel tissue targets. For example, nematodes residing in the hemolymph may release bacteria with virulence factors targeting neurons or neuromuscular junctions. The first section of this review focuses on toxins and their context in agriculture. The second describes the mode of action of toxins from common entomopathogens and the third draws comparisons between Gram positive and Gram negative bacteria. The fourth section reviews the implications of the nervous system in biocontrol.

Role of pore-forming toxins in bacterial infectious diseases

Pore-forming toxins (PFTs) are the most common bacterial cytotoxic proteins and are required for virulence in a large number of important pathogens, including Streptococcus pneumoniae, group A and B streptococci, Staphylococcus aureus, Escherichia coli, and Mycobacterium tuberculosis. PFTs generally disrupt host cell membranes, but they can have additional effects independent of pore formation. Substantial effort has been devoted to understanding the molecular mechanisms underlying the functions of certain model PFTs. Likewise, specific host pathways mediating survival and immune responses in the face of toxin-mediated cellular damage have been delineated. However, less is known about the overall functions of PFTs during infection in vivo. This review focuses on common themes in the area of PFT biology, with an emphasis on studies addressing the roles of PFTs in in vivo and ex vivo models of colonization or infection. Common functions of PFTs include disruption of epithelial barrier function and evasion of host immune responses, which contribute to bacterial growth and spreading. The widespread nature of PFTs make this group of toxins an attractive target for the development of new virulence-targeted therapies that may have broad activity against human pathogens.

The evidence on the degradation processes in the midgut epithelial cells of the larval antlion Euroleon nostras (Geoffroy in Fourcroy, 1785) (Myrmeleontidae, Neuroptera)

We analysed structural differences between midgut epithelial cells of fed instar antlions' larvae Euroleon nostras and starved ones. In starved larvae the presence of autophagolysosome-like structures was observed, which are characteristic structures associated with autophagy. The results presented here provide insight supporting the role of autophagy as a cell survival mechanism for the periods of food deprivation. Additional structural changes in the cytoplasm were seen in the spherites. The ultrastructure and chemical composition of spherites in the midgut epithelial cells of first, second and third instar larvae were observed with light microscopy and transmission electron microscopy (TEM). A detailed characterization of the elemental composition of the spherites was studied using analytical electron microscopy; a combination of energy dispersive X-ray spectroscopy (EDXS), electron energy-loss spectroscopy (EELS) and energy filtering TEM (EFTEM) was applied. The structure and elemental composition of the spherites changed during the period of larval life. Moreover, changes in chemical composition were found between spherites from fed and starved E. nostras. In fed first instar larvae, the spherites contained an organic matrix, composed of C, N and O. In this matrix, P, Cl, Ca and Fe were detected. In starved first instar larvae, only C, N and P were present. The spherites of fed second instar larvae were rich in organic and inorganic elements and were composed of C, N, O, Na, Mg, P, S, Cl, K, Ca, Mn, Fe and Zn. In starved second instar larvae, the chemical elements N, O, P, Ca and Fe were found. In fed third instar larvae, the spherites contained C, N, O, Na, Mg, P, Cl, K, Ca, Mn, Fe, Co and Zn. In starved third larvae, C, O, Si, Ca, and Fe were detected. Generally, the spherites are exploited in starved larvae. These results suggest that the elemental supply of spherites may provide crucial support for physiological processes during starvation periods amongst E. nostras instar larvae. In some cases in fed second and fed third instar larvae, spherites were seen in the lumen of the midgut. Such spherites could serve as reservoirs for nontoxic waste material that cannot be metabolized.

The bacterium, Lysinibacillus sphaericus, as an insect pathogen

Since the first bacteria with insecticidal activity against mosquito larvae were reported in the 1960s, many have been described, with the most potent being isolates of Bacillus thuringiensis or Lysinibacillus sphaericus (formerly and best known as Bacillus sphaericus). Given environmental concerns over the use of broad spectrum synthetic chemical insecticides and the evolution of resistance to these, industry placed emphasis on the development of bacteria as alternative control agents. To date, numerous commercial formulations of B. thuringiensis subsp. israelensis (Bti) are available in many countries for control of nuisance and vector mosquitoes. Within the past few years, commercial formulations of L. sphaericus (Ls) have become available. Because Bti has been in use for more than 30 years, its properties are well know, more so than those of Ls. Thus, the purpose of this review is to summarise the most critical aspects of Ls and the various proteins that account for its insecticidal properties, especially the mosquitocidal activity of the most common isolates studied. Data are reviewed for the binary toxin, which accounts for the activity of sporulated cells, as well as for other toxins produced during vegetative growth, including sphaericolysin (active against cockroaches and caterpillars) and the different mosquitocidal Mtx and Cry toxins. Future studies of these could well lead to novel potent and environmentally compatible insecticidal products for controlling a range of insect pests and vectors of disease.

Application of analytical electron microscopic methods to investigate the function of spherites in the midgut of the larval antlion Euroleon nostras (Neuroptera: Myrmeleontidae)

This study presents an application of analytical electron microscopy in biology to investigate the chemical composition of the spherites and to elucidate the importance of these methods in the life sciences. The structure of the spherites in the midgut cells of first, second, and third instar larvae Euroleon nostras was investigated by a combination of transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDXS), electron energy-loss spectroscopy (EELS), and energy filtering TEM (EFTEM). The structure and chemical composition of the spherites changed during the metamorphosis. In first larvae, the spherites are composed of amorphous, flocculent material, containing C, N, and O. In second larvae and third ones, the spherites have concentric layers of alternating electron-dense and electron-lucent material. In second larvae, Si, P, Ca, and Fe are accumulated in the spherite organic matrix, composed of C, N, and O. In the spherites of third larvae, additionally Al was found. Therefore, the spherites are thought to store organic compounds in all three larval stages of E. nostras and additionally inorganic compounds in second and third ones. In first larvae, spherites are present in the midgut cells; in second and third larvae, they are present in the cells of the midgut and in its lumen. It could be suggested that the spherites might be involved in the regulation of the appropriate mineral composition of the internal environment and could serve as the accumulation site of nontoxic waste materials that cannot be metabolized.

Properties and applied use of the mosquitocidal bacterium, Bacillus sphaericus

Strains of Bacillus sphaericus exhibit varying levels of virulence against mosquito larvae. The most potent strain, B. sphaericus 2362, which is the active ingredient in the commercial product VectoLex^®, together with another well-known larvicide Bacillus thuringiensis subsp. israelensis, are used to control vector and nuisance mosquito larvae in many regions of the world. Although not all strains of B. sphaericus are mosquitocidal, lethal strains produce one or two combinations of three different types of toxins. These are (1) the binary toxin (Bin) composed of two proteins of 42 kDa (BinA) and 51 kDa (BinB), which are synthesized during sporulation and co-crystallize, (2) the soluble mosquitocidal toxins (Mtx1, Mtx2 and Mtx3) produced during vegetative growth, and (3) the two-component crystal toxin (Cry48Aa1/Cry49Aa1). Non-mosquitocidal toxins are also produced by certain strains of B. sphaericus, for examples sphaericolysin, a novel insecticidal protein toxic to cockroaches. Larvicides based on B. sphaericus-based have the advantage of longer persistence in treated habitats compared to B. thuringiensis subsp. israelensis. However, resistance is a much greater threat, and has already emerged at significant levels in field populations in China and Thailand treated with B. sphaericus. This likely occurred because toxicity depends principally on Bin rather than various combinations of crystal (Cry) and cytolytic (Cyt) toxins present in B. thuringiensis subsp. israelensis. Here we review both the general characteristics of B. sphaericus, particularly as they relate to larvicidal isolates, and strategies or considerations for engineering more potent strains of this bacterium that contain built-in mechanisms that delay or overcome resistance to Bin in natural mosquito populations.

The MACPF/CDC family of pore-forming toxins

Pore-forming toxins (PFTs) are commonly associated with bacterial pathogenesis. In eukaryotes, however, PFTs operate in the immune system or are deployed for attacking prey (e.g. venoms). This review focuses upon two families of globular protein PFTs: the cholesterol-dependent cytolysins (CDCs) and the membrane attack complex/perforin superfamily (MACPF). CDCs are produced by Gram-positive bacteria and lyse or permeabilize host cells or intracellular organelles during infection. In eukaryotes, MACPF proteins have both lytic and non-lytic roles and function in immunity, invasion and development. The structure and molecular mechanism of several CDCs are relatively well characterized. Pore formation involves oligomerization and assembly of soluble monomers into a ring-shaped pre-pore which undergoes conformational change to insert into membranes, forming a large amphipathic transmembrane β-barrel. In contrast, the structure and mechanism of MACPF proteins has remained obscure. Recent crystallographic studies now reveal that although MACPF and CDCs are extremely divergent at the sequence level, they share a common fold. Together with biochemical studies, these structural data suggest that lytic MACPF proteins use a CDC-like mechanism of membrane disruption, and will help understand the roles these proteins play in immunity and development.

Complete genome sequence of the mosquitocidal bacterium Bacillus sphaericus C3-41 and comparison with those of closely related Bacillus species

Bacillus sphaericus strain C3-41 is an aerobic, mesophilic, spore-forming bacterium that has been used with great success in mosquito control programs worldwide. Genome sequencing revealed that the complete genome of this entomopathogenic bacterium is composed of a chromosomal replicon of 4,639,821 bp and a plasmid replicon of 177,642 bp, containing 4,786 and 186 potential protein-coding sequences, respectively. Comparison of the genome with other published sequences indicated that the B. sphaericus C3-41 chromosome is most similar to that of Bacillus sp. strain NRRL B-14905, a marine species that, like B. sphaericus, is unable to metabolize polysaccharides. The lack of key enzymes and sugar transport systems in the two bacteria appears to be the main reason for this inability, and the abundance of proteolytic enzymes and transport systems may endow these bacteria with exclusive metabolic pathways for a wide variety of organic compounds and amino acids. The genes shared between B. sphaericus C3-41 and Bacillus sp. strain NRRL B-14905, including mobile genetic elements, membrane-associated proteins, and transport systems, demonstrated that these two species are a biologically and phylogenetically divergent group. Knowledge of the genome sequence of B. sphaericus C3-41 thus increases our understanding of the bacilli and may also offer prospects for future genetic improvement of this important biological control agent.