Delestrait Guillaume

  Master thesis of Guillaume Delestrait

Nanoscale study of flagella in Bacillus thuringiensis strains

The Bacillus cereus sensu lato group, a very homogeneous cluster within the Bacillus genus, comprises six recognized species: B. cereus sensu stricto, B. thuringiensis, B. anthracis, B. mycoides, B. pseudomycoides and B. weihenstephanensis [1]. These bacteria are Gram-positive spore-forming, aerobic-to-facultative, rod-shaped, and widely distributed environmentally [2]. The B. cereus group species exhibit remarkably similar genetic background, cell structure and physiology. However, the pathogenic potential and diverse host range have defined the members of this group. For example, whereas B. thuringiensis is an entomopathogenic bacterium used as bioinsecticide [3], B. cereus is known mainly as an opportunistic food poisoning pathogen able to cause diarrhoea and vomiting syndromes [2]. Additionally, B. anthracis, the etiological agent of anthrax, is found worldwide and is able to infect virtually all mammals [4]. Since these bacteria are potentially enterotoxic to humans or insects, the nanoscale analysis of their cell surface components has become an important issue. Particularly, several studies using B. cereus and B. thuringiensis isolates have demonstrated that swarming (flagellum-driven motility) is necessary for biofilm formation and it is coupled with an increased secretion of certain hemolysis [5, 6]. Moreover, there is growing evidence that flagella are important organelles for cell surface interactions, including bacteria-host interactions.

In the frame of a close collaboration between Prof. Mahillon team (ELI-ELIM, UCL) and Prof. Dufrêne team (IMCN-BSMA, UCL), we are using atomic force microscopy (AFM) in order to analyze the cell surface properties and morphology of different B. thuringiensis strains with emphasis on flagella arrangement and expression. The general strategy of this project involves (i) improving techniques for surface analysis (advanced procedures for sample preparation, and tip modifications, high-resolution imaging, single-molecule manipulations), and (ii) applying these nanotools to a range of different B. thuringiensis strains. Shown here below are two AFM images of flagellated (left) and non-flagellated (right) Bacillus thuringiensis strains.

References:
[1] Jensen GB, Hansen BM, Eilenberg J, Mahillon, J. (2003) The hidden lifestyles of Bacillus cereus and relatives. Environ Microbiol. 5: 631-640.
[2] Bottone, EJ. (2010) Bacillus cereus: a volatile human pathogen. Clin. Microbiol. Rev. 23, 382-398.
[3] Bravo A, Gill SS, Soberón M. (2007) Mode of action of Bacillus thuringiensis Cry and Cyt toxins and their potential for insect control. Toxicon 49: 423-435.
[4] Klee SR, Brzuszkiewicz EB, Nattermann H, Brüggemann H, Dupke S, et al. (2010) The Genome of a Bacillus isolate causing Anthrax in Chimpanzees combines chromosomal properties of B. cereus with B. anthracis virulence plasmids. PLoS ONE 5: e10986.
[6] Ghelardi, E, Celandroni, F, Salvetti, S, Ceragioli, M, Beecher, DJ, et al. (2007) Swarming behavior and hemolysin BL secretion by Bacillus cereus. Appl. Environ. Microbiol. 73: 4089-4093.
[7] Houry, A, Briandet, R, Aymerich, S, Gohar, M. (2010) Involvement of motility and flagella in Bacillus cereus biofilm formation. Microbiology 156: 1009-1018.