Isolation,identification and genetic organization of the ADI operon in <Emphasis Type="Italic">Enterococcus faecium</Emphasis> GR7

L-Arginine is an indispensable amino acid, as it is required for normal growth of microbes, plants and animals (Szende et al., Cancer Cell Int 1:1475–1480, 2001). Arginine deiminase is the first enzyme of arginine deiminase (ADI) pathway, which catalyzes the conversion of arginine to citrulline and ammonia in an irreversible reaction. Lactic acid bacteria isolated from dairy products were investigated for their ability to hydrolyze arginine. Citrulline production in many LAB strains suggests that the arginine metabolism takes place via the arginine deiminase pathway. The highest arginine deiminase specific activity (0.27 IU/mg) was reported in isolate GR7, which was characterized morphologically, biochemically and by 16S rRNA gene sequencing as Enterococcus faecium. Genetic organization of the ADI operon in E. faecium GR7 was further studied using various molecular biology and computational techniques. Sequence analysis revealed that the genes involved in arginine catabolism are clustered together in an operon (3,906 bp) consisting of the genes arcA (arginine deiminase), arcB (ornithine transcarbamylase), and arcC (carbamate kinase), which are localized on the anti-sense strand of genomic DNA. Nucleotide sequence analysis revealed three open reading frames (ORFs) that were arranged contiguously and transcribed in the same direction, as an apparent operon. The genes followed the order arcC, arcB, arcA, which differs from that found in other microorganisms. The information obtained in this study provides the basis for testing the potential of arginine catabolism to control the emergence of arginine auxotrophic tumors.