Involved in the catabolism of arginine. H2O + L-arginine = L-ornithine + urea Binds 2 manganese ions per subunit. Nitrogen metabolism; urea cycle; L-ornithine and urea from L-arginine: step 1/1. Part of the rocDEF operon. Expression is sigma L dependent, induced by arginine, ornithine or proline. Cells lacking this gene do not grow on arginine as a sole nitrogen source, but do grow on ornithine or ammonium chloride. Belongs to the arginase family.