J. Basic Microbiol. 43 (2003) 6, 534 – 538 DOI: 10.1002/jobm.200310297 © 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 0233-111X/03/612-0534 Short Note (Olson Biochemistry Laboratories, Department of Chemistry and Biochemistry, South Dakota State University, Brookings, SD 57007, USA) Influence of carbon source on pyrimidine synthesis in Pseudomonas mendocina MANUEL F. SANTIAGO 1 and THOMAS P. WEST* (Received 24 April 2003/Accepted 26 June 2003) The effect of carbon source on the regulation of the de novo pyrimidine biosynthetic enzymes in the bacterium Pseudomonas mendocina was studied. When glucose was the carbon source, orotic acid supplementation of P. mendocina cells produced the greatest depression of aspartate transcarbamoy- lase, dihydroorotate dehydrogenase and orotate phosphoribosyltransferase activities while P. mendocina cells grown in the presence of uracil caused the maximal decrease in dihydroorotase and OMP decarboxylase activities. After the pyrimidine starvation of an orotate phosphoribosyltransferase mutant strain of P. mendocina grown on glucose, the pyrimidine biosynthetic pathway enzyme activi- ties were generally diminished. With respect to pyrimidine starvation studies, the carbon source glucose appeared to lessen regulation at the level of enzyme synthesis compared to what has been observed when succinate served as the carbon source. The regulation of the pyrimidine biosynthetic pathway by carbon source in P. mendocina appeared to differ from how carbon source influenced the control of pyrimidine biosynthesis in the closely-related species Pseudomonas stutzeri. Since clinical isolates of the two species classified within the Pseudomonas stutzeri DNA homology group have been found to be of medical importance (POTVLIEGE et al. 1987, ARAGONE et al. 1992), it would seem to be important to study the regulation of nucleic acid metabolism in the P. stutzeri DNA homology group member Pseudomonas mendocina (DE VOS and DE LEY 1983). More specifically, it was of interest to determine how carbon source affects the regulation of pyrimidine biosynthesis in P. mendocina. The de novo pyrimidine biosynthetic pathway utilizes five enzymes to ultimately produce UMP. The genes pyrB, pyrC, pyrD, pyrE and pyrF encode the pathway enzymes aspartate transcarbamoylase (EC 2.1.3.2), dihydroorotase (EC 3.5.2.3), dihydroorotate dehydrogenase (EC 1.3.3.1), orotate phosphoribosyltransferase (EC 2.4.2.10) and orotidine 5′-monophosphate (OMP) decarboxy- lase (EC 4.1.1.23), respectively (O’DONOVAN and NEUHARD 1970). Although various studies have investigated pyrimidine biosynthesis in a number of species of Pseudomonas (ISAAC and HOLLOWAY 1968, CONDON et al. 1976, CHU and WEST 1990, WEST 1994, 1997, SANTIAGO and WEST 2002a), the effect of carbon source on the regulation of pyrimidine biosynthetic enzyme synthesis in pseudomonads has not been fully explored. In this work, pyrimidine biosynthesis in P. mendocina ATCC 25411 was investigated for the influence of carbon source on its regulation by pyrimidines at the level of enzyme synthesis. The findings of this analysis should allow a comparison to be made between the type strains of P. mendocina and the taxonomically-related species P. stutzeri relative to the effect of carbon source on pyrimidine synthesis regulation (DE VOS and DE LEY 1983). 1 Present address: Department of Chemistry, University of Tennessee at Chattanooga, 615 McCallie Avenue, Chattanooga, TN 37403-2598, USA * Corresponding author: Dr. T. P. WEST; e-mail: Thomas_West@sdstate.edu