Carbamoyl-phosphate synthetases (CPS) in lactic acid bacteria and other Gram-positive bacteria

Abstract

Carbamoyl-phosphate synthetases (CPS) catalyze carbamoyl phosphate (CP) biosynthesis from glutamine, bicarbonate and ATP. CPS are formed of two subunits, a small glutaminase subunit and a large synthetase subunit. CP is a common intermediate of arginine and pyrimidine biosynthesis. CPS in prokaryotes are either arginine-regulated (CPS-A), pyrimidine-regulated (CPS-P) or regulated by both components. Two to zero CPS are present in the four lactic acid bacteria studied (Lactobacillus plantarum, Enterococcus faecalis, Lactococcus lactis and Lactobacillus delbrueckii ssp. lactis). Only L. plantarum harbours two CPS with a CPS-P providing CP for both metabolic pathways. CPS-A can only supplement CP for arginine biosynthesis in higher concentrations of CO2 or bicarbonate. The CPS-P present in L. plantarum and E. faecalis is encoded by genes within the pyr operon, and genes dispersed within the chromosome in Lc. lactis. CPS is absent in L. delbrueckii ssp. lactis and the catabolism of arginine via the arginine deiminase pathway (ADI) provides the CP for pyrimidine biosynthesis. In addition to their functional CPS-P, E. faecalis and Lc. lactis also harbour an ADI pathway so that arginine catabolism may regulate CP biosynthesis in these species. Lactic acid bacteria CPS were compared to CPS of 13 Gram-positive bacteria with sequenced or partially sequenced genomes. Most organisms harbour a CPS-P. CPS-P is also found in the few organisms (L. plantarum, B. subtilis and B. stearothermophilus) which harbour a CPS-A. The number of CPS and the organization of their genes is variable in Gram-positive bacteria.