Production of β-N-acetylglucosaminidase and chitinase by Aeromonas species isolated from river fish

The beta-N-acetylglucosaminidase (beta-GlcNAcase)- and chitinase-producing abilities of 283 strains in Aeromonas species from intestinal tracts of common carp Cyprinus carpio, crucian carp Carassius auratus, and gray mullet Mugil cephalus, and from their environment were determined using three fluorogenic 4-methylumbelliferone glycosides of N-acetylglucosamine oligosaccharides. As many as 91 to 100% of strains in each Aeromonas species produced at least one of three enzymes, such as beta-GlcNAcase, exo-chitinase and endo-chitinase, and 58 to 80% of strains could produce all three enzymes. Enzyme activities varied remarkably with species and strains, along with bacterial sources, and 20 to 55% of A. hydrophila (except for beta-GlcNAcase), A. jandaei (except for beta-GlcNAcase) and A. sobria showed high activities (> 0.1 U/mg) of beta-GlcNAcase and chitinase. Moreover, there was a significant strain-to-strain variation in composition of chitinoclastic enzymes even within genospecies. These results suggest that the predominant aeromonads in the intestine of freshwater fish play an important role in the digestion of injested chitin-bearing organisms.