Carbon Dioxide Requirement of Various Species of Rumen Bacteria

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Abstract
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.