Influence of Culture Eh on the Growth and Metabolism of the Rumen Bacteria Selenomonas ruminantium, Bacteroides amylophilus, Bacteroides succinogenes and Streptococcus bovis in Batch Culture

Abstract

One facultatively and three strictly anaerobic rumen bacteria were grown in pH-controlled anaerobic batch cultures in which the E h of the medium was regulated by the addition of titanium (III) citrate solution at values below −50 mV and potassium ferricyanide above −50 mV. Growth occurred over a wide range of E h, with the maximum limit being +360, + 250, +175 and +414 mV for Selenomonas ruminantium, Bacteroides amylophilus, Bacteroides succinogenes and the aerotolerant Streptococcus bovis, respectively. Changes in E h had little influence on the growth yield or ratios of fermentation end-products in these bacteria over a fairly wide range, although the specific growth rate of all species tended to decline at E h values above 0 mV. Abnormal, elongated forms of Sel. ruminantium and B. succinogenes predominated at high E h. It was concluded that O2, and not a high E h, is the toxic factor in ‘oxidized’ anaerobic growth medium, and that it would not normally be necessary to regulate E h closely in experiments where the growth and metabolism of these bacteria is under study, provided that O2-free conditions were maintained.