Utilization of CO 2 and Acetate in Amino Acid Synthesis by Streptococcus bovis. ∗

Carbon dioxide exerts a marked influence on the metabolic activities and nutritional requirements of Streptococcus bovis. A requirement for CO₂ exists when some strains are grown in media containing simple nitrogen sources(1–4); in other strains of S. bovis, CO₂ is involved in the production of polysaccharides (5–6), and of destransucrase(7). Acetate also affects the metabolism of S. bovis. Bailey and Oxford found that it was required for dextran synthesis(6), and we demonstrated its ability to stimulate growth and to be incorporated into cells growing in an ammonium medium(3).

This paper reports the utilization of CO₂ and acetate in amino acid synthesis by S. bovis growing on different nitrogen sources, and elaborates further some of the nutritional requirements for growth of this organism in the absence of CO₂.

Materials and methods. Microbiological. The organism used was Streptococcus bovis strain P 10. Procedures for maintenance of cultures, performance of growth tests, and preparation of inocula were identical to those previously described(8). The basal medium was that of Prescott and Stutts(1), supplemented as indicated below with nitrogen sources consisting of (i) L-arginine, (ii) ammonium acetate, or (iii), the complex amino acid mixture of Henderson and Snell(9). Some growth experiments requiring removal of CO₂ were performed with special flasks, (10), but usually, cultures were grown in 50 ml Erlenmeyer flasks, stoppered with porous plastic plugs, and incubated over 20% KOH in large vacuum desiccators. Shredded filter paper was immersed in the KOH solution to increase surface area, and the desiccator was evacuated to approximately 40 mm. In some experiments, cultures were incubated over the KOH in vacuo; in others, air was readmitted through a trap containing 20% KOH. The CO₂ was supplied to cultures either as a filter-sterilized NaHCO₃ solution, or as a gaseous atmosphere.