The function of C02-related growth-promoting effect in the orangecolored Streptococcus bovis was investigated. In the defined medium, CO2 requirement was very large compared with that in natural media. Most of 14C02 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 14C02 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 02 in natural media.

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Experiments with 14C-labeled glucose indicated that the orange-colored variety of Streptococcus bovis assimilated about 12 % of consumed glucose in the synthetic medium and 6 % in the peptone-yeast extract medium. These values are very much higher than those of ordinary lactic streptococci which show the values of around 0.4%. Although the yield of lactic acid did not exceed 90 % of consumed glucose, this species is also a homofermenter if the assimilated glucose is taken into account. Different from ordinary lactic acid bacteria, S. bovis can grow in the medium containing ammonium salt as a sole source of nitrogen but organic nitrogen is preferable even for this species.The characteristics of orange-colored cocci isolated from bovine rumen were described by 01 et al. (1-3). The cocci were determined to be a variety of Streptococcus bovis Orla-Jensen, for reason of many similarities except for the pigmentation. They also reported that the lactic acid recovery from fermented glucose by this organism was much less than the theoretical value of homo-lactic fermentation.The pigmentation developed in nutritionally poor medium, and growth yield was markedly higher than other homo-lactic fermenters. The orange coloration in S. bovis had already been noticed by HUNGATE (4) but his description on this point was very slight. This paper describes the glucose metabolism of the orange-colored S. bovis. MATERIALS AND METHODS.

The growth yield of orange-colored Streptococcus boils No. 148 isolated from bovine rumen was investigated. The high growth yield of S. bovis occurred in the presence of C02 under batch culture conditions, and the maximum value for YATP (the gram dry weight of organism produced per mol of ATP) was about 18. The growth yield was decreased by the addition of NaHC03 or Na2C03 which are commonly used as neutralizing agents for the culture of ordinary rumen bacteria. The growth-promoting effect of C02 could be partially replaced by some unsaturated fatty acids and oleate-containing compounds.

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