The carbon dioxide requirement of 32 strains of rumen bacteria, representing 11 different species, was studied in detail. Increasing concentrations of CO(2) were added as NaHCO(3) to a specially prepared CO(2)-free medium which was tubed and inoculated under nitrogen. Prior depletion of CO(2) in the inoculum was found to affect the level of requirement; however, the complexity and buffering capacity of the medium did not appear to be involved. An absolute requirement for CO(2) was observed for eight strains of Bacteroides ruminicola, three strains of Bacteroides succinogenes, four strains of Ruminococcus flavefaciens, two strains of Lachnospira multiparus, one strain of Succinimonas amylolytica, and two strains of Butyrivibrio fibrisolvens. Inconsistent growth responses were obtained in CO(2)-free media with one strain each of B. fibrisolvens, Ruminococcus albus, and Selenomonas ruminantium. Growth of six additional strains of B. fibrisolvens, and single strains of Eubacterium ruminantium and Succinivibrio dextrinosolvens was markedly increased or stimulated by increasing concentrations of CO(2). Peptostreptococcus elsdenii B159 was the only organism tested which appeared to have no requirement, either absolute or partial, for CO(2). Higher concentrations of CO(2) were required for the initiation of growth, as well as for optimal growth, by those species which produce succinic acid as one of their primary end products.
Agar Bacteria