A collagen-like glycoprotein BclS is involved in the formation of filamentous structures of the exosporium of Lysinibacillus sphaericus.

Ni Zhao, Yong Ge, Tingyu Shi, Xiaomin Hu and Zhiming Yuan

Appl Environ Microbiol. 2014 Aug 22. pii: AEM.02238-14.

Abstract

      Lysinibacillus sphaericus produces mosquitocidal binary toxins (Bin toxins) deposited within a balloon-like exosporium during sporulation. Unlike Bacillus cereus group strains, the exosporium of L. sphaericus is usually devoid of the hair-like nap, an external filamentous structure formed by a collagen-like protein BclA. In this study, a new collagen-like exosporium protein, Bsph_0411 (encoding BclS), was characterized from L. sphaericus C3-41. Thin-section electron microscopy revealed that deletion of bclS resulted in loss of the filamentous structures which attached to the exosporium basal layer and spread through the interspace of spores. In vivo visualization of BclS-GFP/mCherry fusion proteins revealed a dynamic pattern of fluorescence that encased the spore from the mother cell-distal (MCD) pole of the forespore, and the BclS-GFP fusions were found to be located in the interspace of the spore as confirmed by 3D super resolution fluorescence microscopy. Further studies demonstrated that the bclS mutant spores were more sensitive to wet heat treatment and germinated at a lower rate than the wild type spores, and that these phenotypes were significantly restored in the bclS complemented strain. These results suggested novel roles of collagen-like protein in exosporium assembly and spore germination, providing a hint for further understanding the genetic basis of the high persistence of Bin toxins in nature.

http://aem.asm.org/content/early/2014/08/19/AEM.02238-14.short