The metabolism of C2 compounds in micro-organisms. 1. The incorporation of [2-14C]acetate by Pseudomonas fluorescens, and by a Corynebacterium, grown on ammonium acetate

Publisher Website
Google Scholar
Abstract
Washed cells of P. fluorescens KB 1, grown on ammonium acetate as sole C source, rapidly oxidize acetate and all the intermediates of the tricarboxylic acid cycle, confirming that this cycle operates in this organism. Cultures of Pseudomonas KB 1 and of the gram positive organism tentatively identified as Corynebacterium sp., growing on ammonium acetate, were incubated for short periods (3 seconds-5 minutes) with 2-C14-acetate. Isotope was incorporated into both the 75% aqueous ethanol-soluble fraction and into protein. The distribution of the incorporated isotope amongst the labeled compounds in the ethanol-soluble fraction showed that intermediates of the tricarboxylic acid cycle, and amino acids directly derived therefrom, rapidly became labeled. Although the proportion of the total radioactivity present in citrate and glutamate was higher than that present in the C4 dicarboxylic acids after establishment of isotopic "steady-state" conditions, the distribution of radioactivity during the earliest stages of the incubation was radically different. Initially, over 70% of the total isotope incorporated was present in C4 compounds. These results show that initially the label was introduced into malate without passing through citrate and that, therefore, a second point of entry of acetate into the tricarboxylic acid cycle must exist in these organisms. These findings are in accordance with the operation in intact cells of the "glyoxylate by-pass" of the tricarboxylic acid cycle, demonstrated in cell extracts. This by-pass serves to replace, from acetate, C4 dicarboxylic acids drained from the tricarboxylic acid cycle when microorganisms grow on this single C source.