Over-production of exopolysaccharide by Lacticaseibacillus rhamnosus CNCM I-3690 strain cutbacks its beneficial effect on the host

Most lactobacilli produce extracellular polysaccharides that are considered to contribute to the probiotic effect of many strains. Lacticaseibacillus rhamnosus CNCM I-3690 is an anti-inflammatory strain able to counterbalance gut barrier dysfunction. In this study ten spontaneous variants of CNCM I-3690 with different EPS-production were generated and characterized by their ropy phenotype, the quantification of the secreted EPS and genetic analysis. Amongst them, two were further analysed in vitro and in vivo: an EPS over-producer (7292) and a low-producer derivative of 7292 (7358, with similar EPS levels than the wild type (WT) strain). Our results showed that 7292 does not have anti-inflammatory profile in vitro, and lost the capacity to adhere to the colonic epithelial cells as well as the protective effect on the permeability. Finally, 7292 lost the protective effects of the WT strain in a murine model of gut dysfunction. Notably, strain 7292 was unable to stimulate goblet cell mucus production and colonic IL-10 production, all key features for the beneficial effect of the WT strain. Furthermore, transcriptome analysis of colonic samples from 7292-treated mice showed a down-regulation of anti-inflammatory genes. Altogether, our results point out that the increase of EPS production in CNCM I-3690 impairs its protective effects and highlight the importance of the correct EPS synthesis for the beneficial effects of this strain.

Role of lactic acid bacteria in fermented vegetables

The consumption of fermented vegetables is widespread throughout the world and represents an important component of the human diet with considerable contribution to the food supply for a world popula­tion in continuous growth. Many of the fermented vegetables share a general process which requires salting and acidification steps. Among the microorganisms responsible for fermentation, lactic acid bacteria are the most relevant with important organoleptic, quality and safety benefits. This review deals with the microbial ecology of fermented vegetables focusing on the biodiversity of lactic acid bacteria, the most important molecular tech­niques used for their identification and genotyping, their importance for the formation of biofilms as well as their use as starter cultures for obtaining high-quality and safe vegetable products.