Zebrafish: a big fish in the study of the gut microbiota.

The importance of the gut microbiota in host health is now well established, but the underlying mechanisms remain poorly understood. Among the animal models used to investigate microbiota-host interactions, the zebrafish (Danio renio) is gaining attention. Several factors contribute to the recent interest in this model, including its low cost, the ability to assess large cohorts, the possibility to obtain germ-free larvae from non-axenic parents, and the availability of optical methodologies to probe the transparent larvae and adults from various genetic lines. We review recent findings on the zebrafish gut microbiota and its modulation by exogenous microbes, nutrition, and environmental factors. We also highlight the potential of this model for assessing the impact of the gut microbiota on brain development.

Systematic Analysis of the Stress-Induced Genomic Instability of Type Three Secretion System in Aeromonas salmonicida subsp. salmonicida.

The type three secretion system (TTSS) locus of Aeromonas salmonicida subsp. salmonicida, located on the plasmid pAsa5, is known to be lost when the bacterium is grown at temperatures of 25 °C. The loss of the locus is due to the recombination of the insertion sequences flanking the TTSS region. However, the mechanism involved in this recombination is still elusive. Here, we analyzed 22 A. salmonicida subsp. salmonicida strains that had already lost their TTSS locus, and we systematically explored another 47 strains for their susceptibility to lose the same locus when grown at 25 °C. It appeared that strains from Europe were more prone to lose their TTSS locus compared to Canadian strains. More specifically, it was not possible to induce TTSS loss in Canadian strains that have AsaGEI2a, a genomic island, and prophage 3, or in Canadian strains without a genomic island. A comparative genomic approach revealed an almost perfect correlation between the presence of a cluster of genes, not yet characterized, and the susceptibility of various groups of strains to lose their locus. This cluster of genes encodes putative proteins with DNA binding capacity and phage proteins. This discovery creates new opportunities in the study of pAsa5 thermosensitivity.