The arginine deiminase pathway enables Bacillus licheniformis to grow anaerobically on arginine. Both the presence of arginine and anaerobiosis are needed to trigger induction of the pathway. In this study we have cloned and sequenced thearc genes encoding the pathway. They appear clustered in an operon-like structure in the order arcA (arginine deiminase), arcB (ornithine carbamoyltransferase),arcD (putative arginine-ornithine antiporter),arcC (carbamate kinase). It was found that B. licheniformis has an arginine repressor, ArgR, homologous to theB. subtilis arginine repressor AhrC. Mutants affected inargR were isolated. These mutants have lost both repression by arginine of the anabolic ornithine carbamoyltransferase and induction of the arginine deiminase pathway. Electrophoretic band shift experiments and DNase I footprinting revealed that in the presence of arginine, ArgR binds to a site upstream from the arcpromoter. The binding site is centered 108 nucleotides upstream from the transcription start point and contains a single Arg box.