Deficiency in Opu Systems Imparts Salt-Sensitivity to .

can be used as a starter strain in fermented foods or as a probiotic. However, it is salt-sensitive. Here, genomes were compared with the genomes of strains of species (, , , and ) that were isolated from fermented foods and show salt tolerance, to identify the basis for the salt-sensitivity of . Osmoprotectant uptake (Opu) systems transport compatible solutes into cells to help them tolerate osmotic stress. , , and each possess five Opu systems (OpuA, OpuB, OpuC, OpuD, and OpuE); has all except OpuB. However, only has the OpuC system. Based on these findings, the and operons, and the and genes, were amplified from . Expression of each of these systems, respectively, in increased salt-tolerance. expressing , , or grew in 10.5% NaCl (w/v), whereas wild-type could not grow in 3.5% NaCl. The salt resistance of was also increased by overexpression of , , , or . These results indicate that the salt-susceptibility of arises because it is deficient in Opu systems.