Contribution of Type VI Secretion System in Adherent-Invasive Escherichia coli to compete with intestinal microbiota
Résumé
Introduction and objectives Adherent Invasive Escherichia coli (AIEC) has a high capacity to implant itself in the microbiota of people with digestive inflammatory diseases, such as Crohn’s disease. This selective advantage is acquired by dint of its genome plasticity that helped it to gain lots of mutations and consequently to use advantageous mechanisms, compared to other bacteria. Among other mechanisms, the type 6 secretion system (T6SS) is a molecular machinery that allows AIEC to secrete effectors in target cells lumen. AIEC possess two functional T6SS, the first (T6SS-1) would secrete effectors against bacteria from digestive microbiota, and the second (T6SS-2) would preferably target eukaryotic cells. Hence, the objective of this study is to observe the impact caused by AIEC’s T6SS in mice on a mucosa-associated microbiota (ileum and colon) in order to identify potential bacterial preys of this secretion system. Materials and Methods Four isogenic mutants have been generated in AIEC LF82 reference strain: LF82ΔT6SS-1; LF82ΔT6SS-2; LF82ΔT6SS-1,2 and LF82ΔTle3 (an identified phospholipase effector from the T6SS-1). Wild-type mice have been infected with AIEC LF82 and the different isogenic mutants for 4 consecutive days at 109 bacteria/ml. Then, 3 days post-infection different groups of mice have been sacrificed. Samples from colon, ileum and feces have been recovered for DNA extraction to analyse microbiota composition by 16S illumina sequencing approach. Results, Discussion and conclusion Variations of fecal microbiota beta diversity between d0 and d10 were observed in mice infected with AIEC LF82. Interestingly, this variation is different when mice are challenged with the LF82ΔT6SS-1,2 invalidated for both T6SS or with LF82ΔT6SS-1. These results signal that T6SS, especially T6SS-1, has a major impact on mice microbiota. In addition, analysis using linear discriminant analyzes (LDA) helps us identify several genera or bacterial species, targeted by AIEC’s T6SS. For example, the genus Oscillospira, described as positively associated with leanness and physiological health, drops remarkably in the presence of T6SS. Analysis of microbiota associated to intestinal mucosa in mice infected with AIEC LF82 and the T6SS mutants should confirm bacterial preys of AIEC bacteria.