We previously demonstrated that Streptococcus mutans expresses a functional agmatine deiminase system (AgDS) encoded by the agmatine-inducible aguBDAC operon (A. R. Griswold, Y. Y. Chen, and R. A. Burne, J. Bacteriol. 186:1902Bacteriol. 186: -1904Bacteriol. 186: , 2004). The AgDS yields ammonia, CO 2 , and ATP while converting agmatine to putrescine and is proposed to augment the acid resistance properties and pathogenic potential of S. mutans. To initiate a study of agu gene regulation, the aguB transcription initiation site was identified by primer extension and a putative 70 -like promoter was mapped 5 to aguB. Analysis of the genome database revealed an open reading frame (SMU.261c) encoding a putative transcriptional regulator located 239 bases upstream of aguB. Inactivation of SMU.261c decreased AgD activity by sevenfold and eliminated agmatine induction. AgD was also found to be induced by certain environmental stresses, including low pH and heat, implying that the AgDS may also be a part of a general stress response pathway of this organism. Interestingly, an AgDS-deficient strain was unable to grow in the presence of 20 mM agmatine, suggesting that the AgDS converts a growth-inhibitory substance into products that can enhance acid tolerance and contribute to the competitive fitness of the organism at low pH. The capacity to detoxify and catabolize agmatine is likely to have major ramifications on oral biofilm ecology.
An operon encoding enzymes of the agmatine deiminase system (AgDS) has been identified in the cariogenic bacterium Streptococcus mutans UA159. The AgDS is regulated by agmatine induction and carbohydrate catabolite repression. Ammonia is produced from agmatine at low pH, suggesting that the AgDS could augment acid tolerance.
The arginine deiminase system (ADS) is of critical importance in oral biofilm pH homeostasis and microbial ecology. The ADS consists of three enzymes. Arginine is hydrolyzed by AD (ArcA) to generate citrulline and ammonia. Citrulline is then converted to ornithine and carbamoylphosphate via ornithine carbamoyltransferase (ArcB). Finally, carbamate kinase (ArcC) transfers a phosphate from carbamoylphosphate to ADP, yielding ATP. Ammonia production from this pathway protects bacteria from lethal acidification, and ATP production provides a source of energy for the cells. The purpose of this study was to initiate a characterization of the arc operon of Streptococcus rattus, the least cariogenic and sole ADS-positive member of the mutans streptococci. Using an arcB gene fragment obtained by degenerate PCRs, the FA-1 arc operon was identified in subgenomic DNA libraries and sequence analysis was performed. Results showed that the genes encoding the AD pathway in S. rattus FA-1 are organized as an arcABCDT-adiR operon gene cluster, including the enzymes of the pathway, an arginine-ornithine antiporter (ArcD) and a putative regulatory protein (AdiR). The arcA transcriptional start site was identified by primer extension, and a 70 -like promoter was mapped 5 to arcA. Reverse transcriptase PCR was used to establish that arcABCDT could be cotranscribed. Reporter gene fusions and AD assays demonstrated that the operon is regulated by substrate induction and catabolite repression, the latter apparently through a CcpA-dependent pathway.
Collectively, these results indicate that, in contrast to other Streptococcus species, the S. mutans Opp system, and particularly the OppA protein, does not represent an important trait required for growth and colonization.
The agmatine deiminase system was identified in seven strains of mutans streptococci. Genes encoding the AgDS of Streptococcus rattus FA-1 were sequenced and found to share homology with the agu genes of Streptococcus mutans UA159. Agmatine inhibited bacterial growth, suggesting that the AgDS degrades a deleterious substance into useful compounds.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.