Isolation of new nitrite-reducing bacteria, and augmentation of nitrite reduction in the rumen by introducing one of the isolated bacteria
2003
Asanuma, N. (Meiji Univ., Kawasaki, Kanagawa (Japan). Faculty of Agriculture) | Yoshii, T. | Hino, T.
Summary Nitrite-reducing bacteria were isolated from dog feces. An isolated bacterium (No. 1) that had the highest ability to reduce nitrite was able to grow in a medium usually used for growing ruminal bacteria. Bacterium No. 1 utilized starch and various sugars, but did not utilize cellulose, suggesting that No. 1 grows in the rumen more readily when concentrate diets are fed than when roughage diets are fed. Based on high similarity of No. 1 in 16S rDNA sequence to Clostridium sp. (>94 %), as well as other characteristics, No. 1 was deduced to be Clostridium sp. No. 1 was suggested to be unable to acquire energy by electron transport phosphorylation coupled with nitrate and/or nitrite reduction. Nitrite reductase (NiR) in No. 1 was localized in the cytosol, and appeared to accept electrons from ferredoxin. The amount of NiR in No. 1 cells increased when nitrite was present in the medium, suggesting that NiR synthesis is stimulated by nitrite. The optimal pH of No. 1 NiR was 6.5, and the Km value was 5 mM. NiR activity was inhibited by ammonia in an allosteric fashion. These enzyme properties were quite different from those of NiR in nitrite-reducing ruminal bacteria. Addition of No. 1 (0.5 % of total cell number of ruminal bacteria) to a culture of mixed ruminal microorganisms markedly augmented nitrite reduction, which alleviated the adverse effect of nitrite on fermentation and cellulose digestion, and greatly reduced methane production. Consequently, it may be beneficial to use No. 1 as a probiotic for reducing ruminal methanogenesis without suppressing overall fermentation and fiber digestion.
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