Aerobic Spore Formers from the Human Intestine: Genomic and Physiological Characterization of Potential Probiotic Strains

A total of thirty-two aerobic spore former strains were isolated from intestinal samples of healthy children and analyzed for their hemolytic and antibiotic-resistance activities. Four strains selected as non-hemolytic and sensitive to all antibiotics recommended as relevant by regulatory agencies were short-listed and evaluated for their in silico and in vitro probiotic potentials. The four selected strains were assigned to the Bacillus velenzensis (MV4 and MV11), B. subtilis (MV24) and Priestia megaterium (formerly Bacillus megaterium) (MV30) species. A genomic analysis indicated that MV4, MV11 and MV24 contained a homolog of the gene coding for the fibrinolytic enzyme nattokinase while only MV30 encoded for a glutamic acid decarboxylase essential to synthesize the neurotransmitter GABA. All four strains showed a strong antioxidant activity, formed biofilm and produced/secreted quorum sensing peptides able to induce a cytoprotective stress response in a model of human intestinal (HT29) cells. Altogether, genomic and physiological data indicate that the analyzed strains do not pose safety concerns and have in vitro probiotic potentials.