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-in sensitive 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 supe roxide dismutase (SOD) activity was 10- to 20-fold higher in L. sake ins th an in L. sake(sens), depending on the growth phase. An oxygen-insensitive m utant 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 toler ance. Damage to proteins in L. sake(sens), was evidenced by the increased p rotein carbonyl content and reduced activities of the [Fe-S]-cluster-contai ning enzymes fumarase and fumarate reductase. This study forms a physiologi cal basis for understanding the significance of elevated oxygen stress as a n additional method for inhibition of microbial growth in relation to food preservation.