Activity of H+-ATPase in ruminal bacteria with special reference to acid tolerance

Batch culture experiments showed that permeabilized cells and membranes of Ruminococcus albus and Fibrobacter succinogenes, acid-intolerant cellulolytic bacteria, have only one-fourth to one-fifth as much HC ATPase as Megasphaera elsdenii and Streptococcus bovis, which are relatively acid tolerant. Even in the cells grown in continuous culture at pH 7.0, the acid-intolerant bacteria contained less than half as much H+ ATPase as the acid-tolerant bacteria. The amounts of H+-ATPase in the acid-tolerant bacteria were increased by more than twofold when the cells were grown at the lowest pH permitting growth, whereas little increase was observed in the case of the acid-intolerant bacteria. These results indicate that the acid-intolerant bacteria not only contain smaller amounts of H+-ATPase at neutral pH but also have a lower capacity to enhance the level of H+-ATPase in response to low pH than the acid-tolerant bacteria, In addition, the H+-ATPases of the acid-intolerant bacteria were more sensitive to low pH than those of the acid-tolerant bacteria, although the optimal pHs were similar.