MODE OF CO 2 FIXATION BY THE MINUTE STREPTOCOCCI

Abstract

The minute streptococci require either oleic acid or an elevated CO2 tension for growth in a casein hydrolyzate medium. Tracer studies indicate that the route of CO2 fixation is via a C3-C1 condensation (Wood-Werkman reaction). Washed CO2-grown whole cells fixed detectable quantities of C14O2 only when resuspended in a complete growth medium. Essentially all radioactivity fixed by cells treated under these conditions was found in B-labeled aspartic acid. Either oxaloacetic acid or elevated levels of aspartic acid replaced the CO2 or oleate requirement in the nutrition of the minute streptococci. The results suggest that oleate may exert its CO2-sparing effect by facilitating the assimilation of aspartate from the growth medium by some unknown mechanism.