Arginine and Citrulline Catabolic Pathways Encoded by the arc Gene Cluster of Lactobacillus brevis ATCC 367

ABSTRACT High concentrations of l -arginine or l -citrulline in the growth medium provided the wine bacterium Lactobacillus brevis with a significant growth advantage. The arginine deiminase pathway (ADI) arc gene cluster of Lactobacillus brevis contains three genes— arcD , arcE1 , and arcE2 —encoding putative l -arginine/ l -ornithine exchangers. Uptake experiments with Lactococcus lactis cells expressing the genes showed that all three transported l -ornithine with affinities in the micromolar range. Similarly, ArcD and ArcE2 transported l -arginine, while ArcE1 transported l -citrulline, an intermediate of the ADI pathway. Chase experiments showed very efficient exchange of l -arginine and l -ornithine by ArcD and ArcE2 and of l -citrulline and l -ornithine by ArcE1. Low affinities (millimolar range) combined with low translocation rates were found for ArcD and ArcE2 with l -citrulline and for ArcE1 with l -arginine. Resting cells of Lactobacillus brevis grown in the presence of l -arginine and l -citrulline rapidly consumed l -arginine and l -citrulline, respectively, while producing ammonia and l -ornithine. About 10% of l -arginine degraded was excreted by the cells as l -citrulline. Degradation of l -arginine and l -citrulline was not subject to carbon catabolite repression by glucose in the medium. At a high medium pH, l -citrulline in the medium was required for induction of the l -citrulline degradation pathway. Pathways are proposed for the catabolic breakdown of l -arginine and l -citrulline that merge at the level of ornithine transcarbamylase in the ADI pathway. l -Arginine uptake is catalyzed by ArcD and/or ArcE2, l -citrulline by ArcE1. l -Citrulline excretion during l -arginine breakdown is proposed to be catalyzed by ArcD and/or ArcE2 through l -arginine/ l -citrulline exchange. IMPORTANCE Lactobacillus brevis , a bacterium isolated from wine, as well as other food environments, expresses a catabolic pathway for the breakdown of l -citrulline in the medium that consists of the l -citrulline /l -ornithine exchanger ArcE1 and part of the catabolic arginine deiminase (ADI) pathway enzymes. The proposed pathways for l -arginine and l -citrulline breakdown provide a mechanism for l -citrulline accumulation in fermented food products that is the precursor of the carcinogen ethyl carbamate.