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Lactobacillus gasseri SF1183 belongs to a subpopulation of bacteria tightly associated to the human ileal epithelium. Cells of SF1183 survive and grow in simulated intestinal and gastric conditions, have a strong antimicrobial activity against Gram-positives and Gram-negatives and secrete molecule(s) sensed by human intestinal cells. We report that the oral administration of SF1183 cells had a protective effect in a murine model of DSS (Dextran-Sulfate-Sodium)-induced colitis. The analysis of the intestinal microbial composition indicated that several bacterial genera were differently represented in the intestine of DSS-treated animals. An overall similar alteration was observed in the microbiota of DSS-treated animals that received SF1183, suggesting that the beneficial role of the probiotic was not played through a reshuffling of the intestinal flora. Based on our in vivo data we propose the SF1183 strain of L. gasseri as a new anti-inflammatory probiotic, potentially useful as a therapeutic agent for the treatment of IBDs.

We identified the recA gene of the moderately thermophilic bacterium Streptococcus thermophilus and investigated the role of its product in the adaptation to heat shock and nutrient starvation. Expression of recA was required for optimal viability and normal cell morphology upon induction of both stresses. Normal induction of GroEL and ClpL in a recA knock-out mutant suggests that the RecA role in heat shock and nutrient starvation response of S. thermophilus is independent from the intracellular accumulation of these stress-specific chaperones.

Bacteria have always been considered ideal organisms for genetic analysis. While this is true for some model organisms, like Escherichia coli , Bacillus subtilis and, more recently, Lactococcus lactis , genetic analysis of other organisms is often prevented by lack of valuable tools, like vectors, transposons and methods for transformation, gene inactivation and random insertional mutagenesis. This is the case of the moderately thermophilic bacterium Streptococcus thermophilus , an organism that, in spite of its widespread use for food fermentations, is only poorly characterized. We report here an insertional mutagenesis system that allows efficient random mutagenesis, easy characterization of the interrupted genes and construction of stable null mutations. This may become a powerful S. thermophilus tool for both genetic analysis and construction of ‘food-grade’ mutants of this biotechnologically relevant microorganism.