초록
<P><I>Lactobacillus panis</I> strain PM1 is an obligatory heterofermentative and aerotolerant microorganism that also produces 1,3-propanediol from glycerol. This study investigated the metabolic responses of <I>L. panis</I> PM1 to oxidative stress under aerobic conditions. Growth under aerobic culture triggered an early entrance of <I>L. panis</I> PM1 into the stationary phase along with marked changes in end-product profiles. A ten-fold higher concentration of hydrogen peroxide was accumulated during aerobic culture compared to microaerobic culture. This H<SUB>2</SUB>O<SUB>2</SUB> level was sufficient for the complete inhibition of <I>L. panis</I> PM1 cell growth, along with a significant reduction in end-products typically found during anaerobic growth. <I>In silico</I> analysis revealed that <I>L. panis</I> possessed two genes for NADH oxidase and NADH peroxidase, but their expression levels were not significantly affected by the presence of oxygen. Specific activities for these two enzymes were observed in crude extracts from <I>L. panis</I> PM1. Enzyme assays demonstrated that the majority of the H<SUB>2</SUB>O<SUB>2</SUB> in the culture media was the product of NADH: H<SUB>2</SUB>O<SUB>2</SUB> oxidase which was constitutively-active under both aerobic and microaerobic conditions; whereas, NADH peroxidase was positively-activated by the presence of oxygen and had a long induction time in contrast to NADH oxidase. These observations indicated that a coupled NADH oxidase - NADH peroxidase system was the main oxidative stress resistance mechanism in <I>L. panis</I> PM1, and was regulated by oxygen availability. Under aerobic conditions, NADH is mainly reoxidized by the NADH oxidase - peroxidase system rather than through the production of ethanol (or 1,3-propanediol or succinic acid production if glycerol or citric acid is available). This system helped <I>L. panis</I> PM1 directly use oxygen in its energy metabolism by producing extra ATP in contrast to homofermentative lactobacilli.</P>