Sympatric soil communities ofBacillus cereus sensu lato: population structure and potential plasmid dynamics of pXO1- and pXO2-like elements

Abstract

Eighty soil-borne Bacillus cereus group isolates were collected from two neighbouring geographical sites in Belgium. Their genetic relationships and population structure were assessed using Multilocus sequence typing analysis of five chromosomal genes, while the contribution of extrachromosomal elements to the population dynamics was gauged by the presence, diversity and transfer capacity of pXO1- and pXO2-like plasmids. Globally, the bacterial population displayed a broad diversity, including an important subpopulation of psychrotolerant isolates related to Bacillus weihenstephanensis. pXO1- and pXO2-like replicons were present in 12% and 21% of the isolates, but no Bacillus anthracis-related toxin genes were found. Furthermore, only one of the isolates containing a pXO2-related plasmid was shown to be able to mobilize small non-self-conjugative plasmids. Interestingly, several B. cereus sensu lato isolates displaying the same sequence type were observed to have different plasmid contents, suggesting the occurrence of horizontal gene exchange. Similarly, a number of pXO2-like replicons with identical sequences were found in distinct bacterial isolates, therefore strongly arguing for lateral transfers among sympatric bacteria.

Is Cytotoxin K from Bacillus cereus a bona fide enterotoxin?

“…Besides, the NJ tree based on six genes (five housekeeping genes and cytK-2) showed the same tendency as other published B. cereus s.l. phylogenetic studies (Auger et al, 2008;Barker et al, 2005;Fagerlund et al, 2007;Fricker et al, 2011;Han et al, 2006;Hu et al, 2009;Kristoffersen et al, 2011). To verify that cytK was not prone to lateral transfer, 30-kb genome fragments centred on the cytK-2 locus (NCBI database) were also investigated.…”

Evolution of the Bacillus cereus Group

“…It is however not known exactly to what extent horizontal transfer of pXO1-and pXO2-like plasmids may occur in the B. cereus sensu lato population. Hu and co-workers however, in a study of 80 soil-borne B. cereus group isolates from sympiatric communities, detected pXO1-and pXO2-like replicons in 12% and 21% of the isolates, respectively, and showed that strains of the same MLST sequence type had different plasmid contents, while a number of pXO2 replicons were hosted by distinct bacterial isolates, strongly arguing for lateral transfers of genetic material among sympiatric bacteria of the B. cereus group (Hu et al 2009b). Given the fact that newly emerging pathogens (CI/CA strains) seem to arise from transfer of such plasmids, that B. cereus strains encoding alternative capsules (G9241) and possibly other virulence traits from plasmid elements exist, and that knowledge of plasmid diversity in the group is rather limiting, a systematic study targeting B. cereus group plasmids seems warranted.…”

Development of a simple method for the rapid identification of organisms causing anthrax by coagglutination test

“…Additionally, the challenges posed by coincidental or non-coincidental presence of pathogenic microorganisms [5] together with closely related nonpathogenic organisms of the same genus [6] necessitate rapid and specific detection techniques for the organisms that can cause anthrax. As anthrax toxin is essential for the development of anthrax and, B. anthracis isolates that lack plasmid encoding anthrax toxin are nonpathogenic, the toxin is the apt target for the diagnosis of disease [7].…”