The Effect of PH on Maximum Bacterial Growth Rate and its Possible Role as a Determinant of Bacterial Competition in the Rumen

Five rumen bacteria were inoculated into media with pH values ranging from 6.7 to 4.7 to determine effects on maximum growth rate. Streptococcus bovis, Bacteroides ruminicola, and Selenomanas ruminantium appeared to be more resistant to low pH than either Butyrivibrio fibrisolvens or Megasphaera elsdenii. S. Bovis, B. ruminicola, and S. ruminantium showed gradual decreases in maximum growth rate as pH decreased while B. fibrisolvens and M. elsdenii showed an abrupt transition to no growth. Comparison of maximum growth rates among microbes at various pH's shows that ranking of growth rate between individual species can be pH dependent. The results suggest that pH can be a significant factor determining competition among bacteria in the rumen.