Identification and characterization of novel systems for oxygen metabolism and anti-oxidative stress protection in anaerobes

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Our purpose is to know the mechanism of O_2 sensitivity of the obligatory anaerobes Clostridium and Bifidomacterium. Clostridium acetobutylicum, which is well known as an efficient acetone-butanol fermenting bacteria, senses the contamination of O_2 in the growth environments quickly and expresses the O_2 responsive genes. In this study, we investigated the function of O_2-responsive nror operon enzymes by purification of the proteins and characterization of their enzymatic activity. We propose that the obligate anaerobe C. acetobutylicum possesses an efficient multi-enzyme complex that can scavenge O_2 and ROS using NROR as a master electron donor protein. The primary factor responsible for aerobic growth inhibition of Bifidobacterium species is proposed to be the production of H_2O_2 in the growth medium. A H_2O_2-forming NADH oxidase was purified from O_2-sensitive Bifidobacterium bifidum and was identified as a b-type DHOD. The kinetic parameters suggested that the enzyme could be involved in H_2O_2 production in highly aerated environments.