PathoBactEvol

Bacteria of the Bacillus cereus group are food-borne disease agents producing heat resistant spores, and as such particularly well adapted to heat-treated foods. Recently, a novel food pathogen, B. cytotoxicus, was characterized, showing emergence of new pathotypes in the group. At the same time, increasing evidence indicates that invertebrates, like insects or worms, could play a role of environmental incubators with a high level of selection and a main reservoir of events for generating bacterial diversity. Nevertheless, the molecular and physiological mechanisms of such adaptation are still obscure. This study wants to address questions on what occurs in gene content during the adaptive evolution of B. cereus in the insect and how it can impact pathogenesis. In particular it is not clear to what extent the hostile environment, like the insect gut, can influence the adaptation potential of the bacteria. In this project we propose to produce the scientific knowledge necessary to understand and assess the risk of emergence of B. cereus strains with with higher virulence. The goal is to set up large-scale laboratory experiments where the evolution is simulated with fluctuating selective pressures. This analysis will illustrate the evolutionary process B. cereus follows to survive within the gut environment and resist the host immune system. The major expected outcome of this new project is to uncover the genetic features of evolution, which may be indicators for emergence of new animal pathogens. This will be done at the molecular level by academic partners, investigating the mechanisms for genetic evolution of B. cereus in one of its natural biotic environments: the insect gut. Experiments will be designed to determine whether the insect is a favourable environment for bacterial evolution and study how temperature can influence the induction of adaptation mechanisms in the insect digestive tract, including transfer of genetic material, through plasmids or bacteriophages. Since B. cereus phages are related to DNA transfer and potentially influence bacterial evolution and adaptation, some of them they will be characterized for elucidating of their role in bacterial adaptation. The work will be based on previous results obtained earlier by some of us in a previously ANR-financed project ANR-05-PNRA-013 BCEREUS. Our aim here is to describe the history of the events which arose during the experiment, explain phenotypic differences in terms of genotypic differences, measure parameters of interest for the evolution of bacterial populations and better understand how different life traits evolve in different conditions, and how this is related to fitness improvement. The proposed research will be task-orientated and would need a large range of disciplines: basic microbiology, microbial ecology, microbial physiology, evolutionary biology, genomics, applied mathematics and computing. It will also make use of high throughput sequencing technologies, bioinformatics and on data already available on fully sequenced Bacillus cereus genomes. Emphasis will be put on comparative whole genome analysis of multiple evolved strains (or lineages) and integration of the genomic and phenotypic data using computational approaches and mathematical models. These genomic and functional approaches are aimed at understanding patterns of molecular evolution and their influence on the genetic structure of living organisms and should, in fine, allow us to produce a functional description and an understanding of the evolutionary patterns of the bacteria of the B. cereus group during interaction with the insect host. The rewards of such an integrated experimental programme could be the construction of a predictive framework of pathogen evolution that could be of direct practical relevance to both the short-term (ecological) and long-term (evolutionary) management of infectious diseases in order to limit the risk of emergence of new pathogens.