CO2 requirements and nucleic acid synthesis by Brucella abortus.

C1402 is fixed in pyrimidines of nucleic acids by Brucella abortus, strain 6232, during growth on complex artificial media (Newton et al., 1954). The incorporation of C02 into pyrimidines appears to be more obligatory in this strain of B. abortus which requires an increased pCO2 than it is in Escherichia coli (Bolton et al., 1952); a finding which suggested that strains of B. abortus which require for growth a partial pressure of CO2 above that in air might lack the ability to utilize exogenous pyrimidines for nucleic acid synthesis. It is known (Ruwet, 1951) that exogenous pyrimidines will not substitute for the increased pCO2 requirement. This could constitute a basic metabolic difference between strains of B. abortus which require an increased PCO2 in air for growth and those strains which grow in air, the latter synthesizing nucleic acid pyrimidines from the free bases and the former requiring C02 for these syntheses. The experiments described in the present communication were designed to test this hypothesis.