Superoxide dismutase plays an important role in the survival of Lactobacillus sake upon exposure to elevated oxygen

In this study, the responses of two Lactobacillus sake strains to elevated oxygen concentrations at 8 degreesC were investigated. L. sake DSM 6333 (L. sake(sens)), unlike L. sake NCFB 2813 (L. sake(ins)), showed a low growth rate in the presence of 90% O-2 and a rapid loss in viability shortly after entry into stationary phase. The steady-state cytosolic superoxide radical (O-2(-)) concentration in L. sake(sens) was 0.134 muM and in the oxygen-insensitive mutant LSUV4 it was 0.013 muM. The nine- to ten-fold decrease in the rate of O-2(-) elimination in L. sakesens indicates the significance of the O-2(-) -scavenging system in protecting against elevated O-2. The superoxide dismutase (SOD) activity was 10- to 20-fold higher in L. sake ins than in L. sake(sens), depending on the growth phase. An oxygen-insensitive mutant of L. sake,ens, designated as strain LSUV4, had a ten-fold higher SOD activity than the wild-type strain, which likely restored its oxygen tolerance. Damage to proteins in L. sake(sens), was evidenced by the increased protein carbonyl content and reduced activities of the [Fe-S]-cluster-containing enzymes fumarase and fumarate reductase. This study forms a physiological basis for understanding the significance of elevated oxygen stress as an additional method for inhibition of microbial growth in relation to food preservation.