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

Carbamoyl-phosphate synthetases (CPS) catalyze carbamoyl phosphate (CP) bio synthesis from glutamine, bicarbonate and ATP. CPS are formed of two subuni ts, a small glutaminase subunit and a large synthetase subunit. CP is a com mon intermediate of arginine and pyrimidine biosynthesis. CPS in prokaryote s are either arginine-regulated (CPS-A), pyrimidine-regulated (CPS-P) or re gulated by both components. Two to zero CPS are present in the four lactic acid bacteria studied (Lactobacillus plantarum, Enterococcus faecalis, Lact ococcus lactis and Lactobacillus delbrueckii ssp. lactis). Only L. plantaru m harbours two CPS with a CPS-P providing CP for both metabolic pathways. C PS-A can only supplement CP for arginine biosynthesis in higher concentrati ons of CO2 or bicarbonate. The CPS-P present in L. plantarum and E. faecali s 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) provide s 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 c atabolism may regulate CP biosynthesis in these species. Lactic acid bacter ia 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. stearothermoph ilus) which harbour a CPS-A. The number of CPS and the organization of thei r genes is variable in Gram-positive bacteria.