Regulation of nitrogen catabolic enzymes in Vibrio alginolyticus

Repression by ammonia of enzyme systems responsible for the utilization of other nitrogen-containing compounds is known as nitrogen catabolite repression or end-product repression, and has been shown to be a control mechanism in Gram-negative organisms such as Escherichia coli, Klebsiella aerogenes, and Salmonella typhimurium [1,2], yeasts [3] and fungi [4]. However, the inducible nitrogen catabolic enzymes, arginase, alanine dehydrogenase and histidase in Gram-positive Bacillus strains are not regulated by nitrogen catabolite repression [5,6]. Although Vibrio alginolyticus is a Gram-negative bacterium, it is similar to Gram-positive Bacillus strains in a number of respects: they produce true extracellular proteases during the stationary growth phase [7-10]; protease production is rifampin-insensitive [11-13] and is subject to endproduct and catabolite repression which is not relieved by cAMP [9,10,14,15]. In Bacillus subtilis and V. alginolyticus, histidine is the inducer of the Hut enzymes [16,17] whereas in E. coli, K. aerogenes and S. typhimurium urocanic acid is the inducer of the Hut operon [18-20]. Since aspects of enzyme regulation in V. alginolyticus resemble those found in Bacillus strains rather than in the more closely related Gram-negative strains, we investigated the phenomenon of nitrogen catabolite repression in V. alginolyticus.