Phylogenetic analysis and gene linkage of ArgR/AhrC orthologs revealed groups of syntenie in Gram-positive bacteria

Arginine regulates genes involved in arginine metabolism at the transcriptional level via an arginine repressor ArgR of Lactobacillus plantarum, also called AhrC in Bacillus subtilis. ArgR and AhrC were used to search for ArgR orthologs in partially- or completely- sequenced genomes. Two to four ArgR-like putative proteins (paralogs) were found in Staphylococcus aureus, Lactococcus lactis, Enterococcus faecalis and in different Streptococcus species. A phylogenetic tree with 41 ArgR-like putative proteins was constructed. When the genes surrounding the argR genes were searched, three groups of associated genes were found. In general, these groups corresponded to ArgR homology clusters in the phylogenetic tree. The argR gene was linked to recN (15 cases including L. plantarum ArgR and B. subtilis AhrC); to arc genes involved in arginine catabolism by the arginine deiminase pathway (7 cases); to arg genes encoding arginine biosynthetic enzymes (3 cases) and to no specific genes in the other cases. The first two gene linkage groups were found in Lc. Lactis, S. aureus and in Streptococcus (S. thermophilus, S. equi, S. mutans, S, pyogenes and S. pneumoniae). In E. faecalis, two out of four copies were contiguous and divergently transcribed. The fact that argR genes linked to specific genes encode homologous groups of ArgR paralogs, suggests that these sets of ArgR proteins may play different roles.