Metabolism of pyrimidine bases and nucleosides by Pseudomonas fluorescens biotype F

Pyrimidine metabolism in Pseudomonas fluorescens biotype F, and its ability to grow in liquid culture on pyrimidines and related compounds was investigated. lt was found that uracil, uridine, cytosine, cytidine, deoxycytidine, dihydrouracil, dihydrothymine. p-alanine or B-aminoisobutyric acid could be utilized by this pseudomonad as a sole nitrogen source. Only uridine. cytidine, 6-alanine, B-aminoisobutyric acid or ribose were capable of supporting its growth as a sole source of carbon. ln solid medium, the pyrimidine analogue S-fluorouracil or S-fluorouridine could prevent P. fluorescens biotype F growth at a low concentration while a 2O-fold higher concentration of S-fluorocytosine, S-fluorodeoxyuridine or 6-azauracil was necessary to block its growth. The pyrimidine salvage enzymes cytosine deaminase, nucleoside hydrolase, uridine phosphorylase, thymidine phosphorylase and cytidine deaminase were assayed. Only cytosine deaminase and nucleoside hydrolase activities could be detected under the assay conditions used. The effect of growth conditions on cytosine deaminase and nucleoside hydrolase levels in the micro-organism was explored. Cytosine deaminase activity was shown to increase if glycerol was substituted for glucose as the sole carbon source or if asparagine replaced (NH4)2SO4 as the sole nitrogen source in each respective medium. ln contrast, nucleoside hydrolase activity remained virtually unchanged whether the carbon source in the medium was glucose or glycerol. A decrease in nucleoside hydrolase activity was witnessed when asparagine was present in the medium instead of (NHo)rSOu as the sole source of nitrogen. lntroduction Pyrimidine metabolism in pseudomonads has been studied far less than in other bacteria (O'Donovan and Neuhard, 1970). The extensive taxonomic classification study of aerobic pseudomonads by Stanier et al. (1966) did not examine whether pyrimidine bases and nucleosides could support their growth. Later studies have investigated the utilization of pyrimidine bases and nucleosides by aerobic pseudomonads. In a comprehensive study of pyrimidine metabolism in Pseudomonas acidoaorans, it was shown that only uracil, cytosine or thymine could support its growth as a sole nitrogen source and that pyrimidines could not sustain $owth ofthis pseudomonad as sole carbon sources (Kelln and $7arren, L974).In Pseudomonas facilis, uracil, dihydrouracil, thymine or dihydrothymine could serve as a sole source of nitrogen (Kramer and Kaltwasser, 1969). A number of studies have investigated the growth of fluorescent pseudomonads on pyrimidines (Fink et a1.,1954; Potter e, a1.,1982; \trflest and Chu, 1985, 1986). Growth on uridine, cytidine, dihydrouracil or dihydrothymine was observed for Pseudnmonas aerugirnsq Pseudamorws chbroraphis and Psadomoras aureofocieru as either a nitrogen or a carbon source. For these pseudgmonads, uracil, thymine or cytosine gupported their growth exclusively as a nitrogen source. Deoxycytidine also supported P. aeruginosa growth only as a nitrogen source. The least versatile of the fluorescent pseudomonads examined was Pseudomonas putida. It grew