Department of Food and Bioproduct Sciences, College of Agriculture and Bioresources, University of Saskatchewan, 51 Campus Drive, Saskatoon, SK, S7N 5A8, Canada.
AMB Express. 2013 Jan 31;3(1):10. doi: 10.1186/2191-0855-3-10.
Lactobacillus panis strain PM1 is an obligatory heterofermentative and aerotolerant microorganism that also produces 1,3-propanediol from glycerol. This study investigated the metabolic responses of L. panis PM1 to oxidative stress under aerobic conditions. Growth under aerobic culture triggered an early entrance of L. panis 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 H2O2 level was sufficient for the complete inhibition of L. panis PM1 cell growth, along with a significant reduction in end-products typically found during anaerobic growth. In silico analysis revealed that L. panis 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 L. panis PM1. Enzyme assays demonstrated that the majority of the H2O2 in the culture media was the product of NADH: H2O2 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 L. panis 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 L. panis PM1 directly use oxygen in its energy metabolism by producing extra ATP in contrast to homofermentative lactobacilli.
植物乳杆菌 PM1 是一种严格的异型发酵兼耐氧微生物，它可以从甘油生产 1,3-丙二醇。本研究探讨了植物乳杆菌 PM1 在有氧条件下对氧化应激的代谢反应。有氧培养下的生长促使植物乳杆菌 PM1 提前进入静止期，同时产物谱发生明显变化。与微氧培养相比，有氧培养时积累了十倍以上的过氧化氢。该 H2O2 水平足以完全抑制植物乳杆菌 PM1 细胞的生长，并显著减少厌氧生长时通常发现的产物。通过计算分析发现，植物乳杆菌具有两个 NADH 氧化酶和 NADH 过氧化物酶基因，但它们的表达水平不受氧气的影响。在植物乳杆菌 PM1 的粗提物中观察到这两种酶的比活性。酶活性测定表明，培养基中大部分 H2O2 是 NADH：H2O2 氧化酶的产物，该酶在有氧和微氧条件下均为组成型活性；而 NADH 过氧化物酶在氧气存在下被正调控激活，与 NADH 氧化酶相比，其诱导时间较长。这些观察结果表明，在植物乳杆菌 PM1 中，NADH 氧化酶-NADH 过氧化物酶偶联系统是主要的抗氧化应激抗性机制，受氧气供应的调节。在有氧条件下，NADH 主要通过 NADH 氧化酶-过氧化物酶系统而不是通过产生乙醇（或 1,3-丙二醇或琥珀酸，如果有甘油或柠檬酸）来重新氧化。与同型发酵乳杆菌相比，该系统有助于植物乳杆菌 PM1 通过产生额外的 ATP 直接将氧气用于其能量代谢。
