ACTIVITY OF H-ATPASE IN RUMINAL BACTERIA WITH SPECIAL REFERENCE TO ACID TOLERANCE()

Batch culture experiments showed that permeabilized cells and membrane s of Ruminococcus albus and Fibrobacter succinogenes, acid-intolerant cellulolytic bacteria, have only one-fourth to one-fifth as much HC AT Pase as Megasphaera elsdenii and Streptococcus bovis, which are relati vely acid tolerant. Even in the cells grown in continuous culture at p H 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 th e acid-tolerant bacteria were increased by more than twofold when the cells were grown at the lowest pH permitting growth, whereas little in crease was observed in the case of the acid-intolerant bacteria. These results indicate that the acid-intolerant bacteria not only contain s maller amounts of H+-ATPase at neutral pH but also have a lower capaci ty to enhance the level of H+-ATPase in response to low pH than the ac id-tolerant bacteria, In addition, the H+-ATPases of the acid-intolera nt bacteria were more sensitive to low pH than those of the acid-toler ant bacteria, although the optimal pHs were similar.