A novel metalloproteinase virulence factor is involved in Bacillus thuringiensis pathogenesis in nematodes and insects

Abstract

The Gram-positive soil bacterium Bacillus thuringiensis has been developed as the leading microbial insecticide for years. The pathogenesis of B. thuringiensis requires common extracellular factors that depend on the PlcR regulon, which regulates a large number of virulence factors; however, the precise role of many of these proteins is not known. In this study, we describe the complete lifecycle of a nematicidal B. thuringiensis strain in the free living nematode Caenorhabditis elegans using in vitro and in vivo molecular techniques to follow host and bacterial effectors during the infection process. We then focus on the metalloproteinase ColB, a collagenase, which was found highly important for destruction of the intestine thereby facilitates the adaptation and colonization of B. thuringiensis in C. elegans. In vivo green fluorescent protein (GFP) reporter-gene studies showed that ColB expression is highly induced and regulated by the global activator PlcR. Finally, we demonstrated that ColB also takes part in B. thuringiensis virulence in an insect model following injection and oral infection. Indeed, addition of purified ColB accelerates the action of Cry toxin proteins in insects, too. These results give novel insights into host adaptation for B. thuringiensis and other B. cereus group bacteria and highlight the role of collagenase metalloproteases to synergize infection process.

Bacillus thuringiensis targets the host intestinal epithelial junctions for successful infection of Caenorhabditis elegans

“…The purified Cry5Ba toxin did not induce the ‘Bob’ phenotype (Kho et al ., ) although it severely damaged of midgut epithelial cells (Peng et al ., ) resulting in shrinkage of the nematode intestine (Wei et al ., ; Peng et al ., ), suggesting that the mechanism of midgut epithelium disruption by Bt infection does not involves Cry toxin action. Therefore, we hypothesized that the epithelial junction may be a target for Bt bacteria to destroy the intestine structures of the nematodes.…”

“…In this work, we analysed the pathogenicity in C. elegans of six nematicidal wild‐type Bt strains (YBT‐1518, C15, G25‐41, G25‐46, G25‐51 and G25‐53) (Zheng et al ., ; Peng et al ., ) and one recombinant Bt strain (BMB0215) (Guo et al ., ) (Supporting Information Table S1). As negative controls we used a non‐nematicidal Bt strain YBT‐1520 (Zhu et al ., ), and an acrystalliferous mutant of Bt strain BMB171 (He et al ., ) (Supporting Information Table S1).…”

“…Indeed, several virulence factors of Bt besides Cry toxins were shown to contribute to the nematodes infection, including the metalloproteases Bmp1 (Luo et al ., ), ColB (Peng et al ., ) and chitinase (Zhang et al ., ). Especially, the Bmp1 and ColB exhibit intestinal tissue degradation activity to enhance the toxicity of Bt (Luo et al ., ; Peng et al ., ). In this study, using Bt ‐C.…”

Spore surface proteins of Brevibacillus laterosporus are involved in insect pathogenesis

“…Future experiments involving combinations of spore surface proteins in different proportions will clarify if such synergisms are involved in the insecticidal action. This is especially true if we imagine entomopathogenesis as a complex process involving the contribution of several factors32.…”

Alcaligenes faecalis ZD02, a Novel Nematicidal Bacterium with an Extracellular Serine Protease Virulence Factor

“…To allow a different visual observation of the effects of A. faecalis ZD02 on worms' intestines, the transgenic worms FT63 (dlg:: gfp) were labeled with green fluorescent protein (GFP) at the intestinal epithelial cell junctions to determine the integrity of the intestine by observing GFP fluorescence (28,29). When FT63 (dlg::gfp) worms were fed E. coli OP50 or BSA, most of their intestines showed an integrated line of clear green fluorescence with a bamboo-like shape under a fluorescence microscope (IX83; Olympus) ( Fig.…”