Fixation and distribution of C14O2 in Brucella abortus.

The requirement of many Brucella abortus strains for a PCO2 of approximately 0.03 atmosphere for growth seems to differ both quantitatively and qualitatively from the C02 requirement of other heterotrophic organisms. In some microorganisms, C02 can be replaced by certain tricarboxylic acids (Lwoff and Monod, 1946; Ajl and Werkman, 1948), amino acids (Lyman et al., 1947; Abelson et al., 1952a, b; McLean and Purdie, 1952), or purines and pyrimidines (Tuttle and Scherp, 1952; Griffin and Racker, 1956). However, attempts to replace the requirement for C02 of B. abortus strains with carboxylic acids, amino acids, purines and pyrimidines, cellular hydrolyzates, and culture filtrates have been unsuccessful (Gerhardt and Wilson, 1950; Ruwet, 1951). In the investigation of the biochemical basis for the C02 requirement of B. abortus strains, Marr and Wilson (1951) have used C1402. They studied the incorporation of C1402 into the amino acids of B. abortus strain 6232, a strain which requires an increased pC02 in air for growth, and found that the major product of C1402 fixation in this strain was glycine. C1402 was fixed, in lesser amounts, into aspartic acid, glutamic acid, alanine, and threonine. C'"02 fixation into the nucleic acids of B. abortus strain 6232 occurs only in the pyrimidines; fixation of C402 into purines seems to be quantitatively insignificant (Newton et al., 1954). When given a choice of pyrimidine precursors, strain 6232 preferred to synthesize pyrimidines from C02 (Newton and Wilson, 1954). In comparative experiments, a mutant strain 6232 capable of growth in air was found to