Tolerance to Low pH and Lactate Production in Rumen Bacteria

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  • ルーメンバクテリアの低pH耐性と乳酸生成能の関係
  • Tolerance to Low pH and Lactate Product

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Abstract

Correlation between the tolerance to low pH and the capacity to produce lactate was examined by comparison among Streptococcus bovis, Selenomonas ruminantium, Butyrivibrio fibrisolvens, and Ruminococcus albus. Generally, acid-tolerant bacteria produced larger amounts per cell mass and higher proportions of lactate than acid-sensitive bacteria. The cellular content of lactate dehydrogenase (LDH) was basically parallel with lactate production with the exception of S. ruminantium, in which lactate production was higher than that accounted for by its LDH content. This could be because the LDH of S. ruminantium has high affinity to pyruvate. The activity of LDH was higher at low pH in acid-tolerant bacteria than acid-sensitive bacteria. The cells grown at low pH contained much larger amounts of LDH than those grown at pH7.0 except for R. albus, the most acid-sensitive bacterium among the bacteria species examined. R. albus, containing an extremely small amount of LDH and producing only a little lactate, was incapable of enhancing LDH content at low pH. In addition, its LDH was most sensitive to low pH and had the lowest affinity to pyruvate. These results suggest that the capacity to produce lactate including the capability to enhance LDH synthesis in response to low pH and the properties of LDH, is in a part related with acid-tolerance.

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