Arginine deiminase in microorganisms.

The arginine deiminase (ADI) pathway comprises three central enzymes, namely arginine deiminase, ornithine transcarbamoylase and carbamate kinase, whose importance is often neglected in reviews of amino acid metabolism in microorganisms. The relevance of the ADI pathway is underscored by the early observations that under anaerobic conditions and in the absence of terminal electron acceptors such as nitrate and nitrite, fermentative arginine breakdown via the ADI system can be used as the sole energy source for bacteria such as Pseudomonas aeruginosa, Bacillus licheniformis and Enterococcus faecalis, where the pathway and its enzymes were originally discovered. The wide distribution of the ADI system further emphasizes its role as a secondary energy-providing pathway in suboptimal or harsh growth conditions, such as low-oxygen, low pH, high-salt and low-carbohydrate environments. Moreover, the generation of ammonia via the ADI system may reduce pH stress in specific microniches containing high concentrations of organic acids. A role for ADI in bacterial survival and pathogenicity has been identified in clinical cultures, as shown for Burkholderia pseudomallei isolates from patients with melioidosis. In food matrices, the ADI system may play a role in the establishment of specific microbial communities, as exemplified by the adaptation of Lactobacillus sakei to fermented meat matrices. Staphylococcus spp., which have significance for both clinical settings and food technology, also seem to benefit from the ADI system, albeit in a species- and even strain-dependent manner.