New Records of Virgibacillus Species Found in Thai Fish Sauce Fermentation

Proteinase-producing bacteria found in fish sauce f ermentation could have their important roles in hydrolyzing protein during the f ish sauce fermentation process. Two strains of proteinase-producing bacteria (SK33 and SK37) were isolated from the first month of Thai fish sauce fermented samples. SK33 and SK37 were Gram-positive rod, endospore-forming and moderately halophilic bacteria. They grew well in tryptic soy broth (with initial pH 7) containing 3-25% NaCl, an d showed poor growth in the absence of NaCl at 35 oC. They did not possess hemolytic activity. meso -Diaminopimelic acid was detected in their cell wall peptidoglycan. The 16S rDNA of the two strains were partially sequenced (DQ910838 and DQ910840). SK33 showed the similarity with SK37 at relatedness value of 82%. When phylogenetic tree analysis was performed, SK33 and SK37 indicated in the same cluster of Virgibacillus halodenitrificans. SK33 and SK37 were similar to V. halodenitrificans DSM10037 95 and 96% similarity, repectively. This is the first report of Virgibacillus sp. found in Thai fish sauce fermentation. The two bacterial strains could hydrolyze fish tissue extra ct from anchovy which was the raw material for fish sauce fermentation and used for t he preparation of fish broth. Virgibacillus sp. SK37 had optimal proteinase production conditi on at 35 °C in fish broth containing 5% NaCl at the initial pH 7, while Virgibacillus sp. SK33 had its optimal proteinase production condition at 40 °C in the fish broth containing 25% NaCl at the initial pH 7. SK33 and SK37 had optimal growth conditions at 18 and 20% NaCl, respectively in fish broth incubated at 35 oC. They could also grow and produce proteinase at pH 5.5-7.5 which was the pH range of fish sauce fermentation. This study reveals that Virgibacillus sp. SK33 and Virgibacillus sp. SK37 could be potential strains for applying as starter cultures to accelerate fish sauce fermen tation.