The function of CO₂-related growth-promoting effect in the orange-colored Streptococcus bovis was investigated. In the defined medium, CO₂ requirement was very large compared with that in natural media. Most of ¹⁴CO₂ incorporated was detected in the protein part. On the other hand, in the Polypepton-yeast extract medium, ¹⁴CO₂ incorporation was extremely small and about 40% of the incorporated ¹⁴CO₂ was found in the lipid part.
Though S. bovis required only biotin as an essential factor among the vitamins, in the Polypepton medium, some of unsaturated fatty acids and oleate-containing compounds could replace not only biotin but also CO₂ requirement, whereas, in the synthetic medium, these compounds could not replace CO₂ requirement. This result suggests that CO₂ takes part in synthesizing not only amino acids but also fatty acids.
S. bovis is sensitive to oxygen, but CO₂ or unsaturated fatty acids can be replaced by O₂ in natural media.