Diversity of thermal ecotypes and potential pathotypes ofBacillus thuringiensissoil isolates

Abstract

Ecological diversification of Bacillus thuringiensis soil isolates was examined to determine whether bacteria adapted to grow at low temperature and/or potentially pathogenic correspond to genetically distinct lineages. Altogether, nine phylogenetic lineages were found among bacilli originating from North-Eastern Poland (n = 24) and Lithuania (n = 25) using multi-locus sequence typing. This clustering was chiefly confirmed by pulsed-field gel electrophoresis. One third of the bacilli were found to be psychrotolerant, which strongly supports the hypothesis of the existence of thermal ecotypes among B. thuringiensis. PCR screening was also performed to detect potential enterotoxin genes and Bacillus anthracis pXO1- and pXO2-like replicons. The cytK-positive isolates (22%) were significantly associated with two phylogenetic lineages (potential CytK pathotypes), whereas there was no correlation between phylogenetic grouping and the presence of the potential tripartite enterotoxin pathotypes (86% of strains). A statistically significant association between phylogenetic lineages and ecologic properties was found with regard to the cry1-positive Lithuanian isolates, while the cry genes in Polish isolates and the pXO1- and pXO2 replicon-like elements showed scattered distribution across phylogenetic lineages. Our results support the hypothesis that B. thuringiensis comprises strains belonging to different phylogenetic lineages, which exhibit specific ecological properties.

Eco-Genetic Structure of Bacillus cereus sensu lato Populations from Different Environments in Northeastern Poland

“…In this study we found lineages of isolates, mostly within clade III, capable of growth at low temperature (thermal ecotypes), as previously observed among B. cereus s.l. and B. thuringiensis [30], [56]. However, in contrast to the previous report [30], in which we found association between the cytotoxic potential with some B. thuringiensis ecotypes, in this study the presence of cytK was mainly associated with isolates from farm samplings where human activity is extensive, while the gene was absent in isolates originating from Białowieża NP.…”

“…However, the above hypothesis was not confirmed in our study as (i) only seven STs included bacilli classified into different species, (ii) the isolates classified to the same species but originated from different habitats exhibited a tendency of clustering to particular complexes, and (iii) B. mycoides isolates showed higher genetic similarity than B. cereus s.s. and B. thuringiensis confirmed statistically by significantly lower number of clonal complexes with high number of isolates (4 CCs; N = 78/84). The previous reports largely focused on B. cereus s.s. , B. anthracis , and/or B. thuringiensis [12], [28], [30]. Here we present for the first time the genetic structure for B. mycoides .…”

“…were isolated as described previously [30]. Bacilli showing rhizoidal growth on the MYP agar (Oxoid, Basingstoke, UK), a selective medium for the B. cereus group, were classified as B. mycoides/B.…”

“…The 534–599 bp fragments originating from these loci were amplified as described previously [30] in the Veriti 96-Well thermal cycler (Applied Biosystems) with the pairs of primers recommended in the B. cereus PubMLST database (http://pubmlst.org/bcereus) (see Table S2). Amplicons were analyzed by the capillary electrophoresis QIAxcel system (Qiagen).…”

Ribosomal background of the Bacillus cereus group thermotypes

“…species makes their classification troublesome17. Therefore, several studies suggested that the B. cereus group should be considered as a single evolutionary unit characterized by clonal expansion and adaptation to various hosts and/or environments that possibly led to the formation of distinct phenotypes, also called ecotypes, within major phylogenetic lineages141819.…”