Bacteria Decomposing Amino Acids in Bulk-Stored Capelin (Mallotus villosus)

Abstract

Bacteria that decompose amino acids were isolated from anaerobically stored capelin (Mallotus villosus) depleted of trimethylamine oxide (TMAO). Some of the 19 isolated strains could be assigned to Lactobacillus, or Bacteroidaceae, but others were not easily identified. Bacteria of the family Bacteroidaceae dominated the anaerobic viable count in the capelin mass in a period after the total reduction of TMAO. Most of the isolated strains differed from each other by decomposing different sets of the free amino acids, or decomposing amino acids at different rates during anaerobic growth in capelin extracts. Most strains isolated from the fish at the later stages of storage, and notably the Bacteroidaceae, produced copious amounts of NH3. Hydrophilic amino acids were the main source of the NH3 produced. Hydrophobic amino acids and other nonprotein nitrogenous components of the capelin extract were not decomposed by any of the 19 organisms, with the exception of the quantitatively less significant hypoxanthine, which was decomposed by three of the strains. Members of the family Bacteroidaceae may be prominent spoilage bacteria in fish, having until now escaped attention because of their obligate anaerobic and psychrotrophic nature.