Comparison of spoilage potential and TorA protein betweenShewanella baltica and Aeromonas salmonicida

To evaluate the differences of spoilage potential of Shewanella and Aeromonas in refrigerated seafood, growth curves and production of trimethylamine (TMA), biogenic amines and total volatile basic nitrogen (TVB-N) in S. baltica and A. salmonicida isolated from Larimichthys crocea were measured at 28 °C and 4 °C. And trimethylamine reductase ( torA ) gene in the two strains were amplified, and similarity, physicochemical properties and spatial structures of TorA protein were compared by bioinformatics. A. salmonicida grew faster at 28 °C, while S. baltica grew faster at 4 °C. Compared with more amount of cadaverine in A. salmonicida , S. baltica produced the higher levels of TMA, biogenic amines, and TVB-N in refrigerated fish juice. The torA genes of 2 490 bp and 1 959 bp were amplified from S. baltica and A. salmonicida respectively, and similarity of TorA protein in its same genus was higher than 97%, and similarity between the two strains was only 36.90%. The molecular weight and isoelectric point of TorA protein in S. baltica were about 92.3 ku and 6.52 , while those were about 90.6 ku and 6.74 in A. salmonicida. The highest amino acid of the predicted protein was glycine and alanine in two strains respectively, resulting in the significant difference of protein spatial structure. The expression levels of torA and ornithine decarboxylase ODC genes in S. baltica were 1.26 and 19.04 times compared to A. salmonicida. Thus, S. baltica and A. salmonicida are psychrophilic spoilage strains in marine products, in which S. baltica has stronger ability to produce amine metabolites due to specific physicochemical properties of TorA protein and its high expression. The study provides theoretical support for revealing the mechanism of microbial spoilage in seafood.