Carbon Dioxide Requirement of Various Species of Rumen Bacteria1

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The carbon dioxide requirement of 32 strains of rumen bacteria, representing 11 different species, was studied in detail. Increasing concentrations of CO2 were added as NaHCO3 to a specially prepared CO2-free medium which was tubed and inoculated under nitrogen. Prior depletion of CO2 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 CO2 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 CO2-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 CO2. Peptostreptococcus elsdenii B159 was the only organism tested which appeared to have no requirement, either absolute or partial, for CO2. Higher concentrations of CO2 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.

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