冷藏大黄鱼SSO希瓦氏菌致腐能力差异机制初探

为探讨特定腐败菌(SSO)希瓦氏菌(Shewanella)致腐能力的差异机制,采用生化和16S rDNA鉴定冷藏大黄鱼货架期终点的产H2S菌,在灭菌鱼汁和无菌鱼块筛选4株致腐差异的希瓦氏菌,扩增氧化三甲胺(TMAO)还原酶基因及分析其表达量,并预测其蛋白质的理化性质。结果显示,22株产H2S菌均为希瓦氏菌属,其中 S.baltica占54.5%,为S. putrefaciens占40.9%,S. hafniensis占4.5%。希瓦氏菌在灭菌鱼汁中致腐能力存在显著差异,其中S. balticaXH2和XH8的缺点评分和TVB-N最高,S. putrefaciensXH14和XH17菌最低。接种无菌鱼块的4株希瓦氏菌中XH2的样品在72h出现腐败气味,48h细菌高于107cfu/g,产生较高的TMA、TVB-N、尸胺和腐胺和,XH8菌次之,XH14和XH17菌最慢。四株希瓦氏菌都扩增出2490bp的torA基因,且torA基因的表达量与致腐能力密切相关,S.balticaXH2最高。预测的TorA蛋白中S.balticaXH2的分子量和不稳定指数最大,理论等电点和总平均疏水性最小。可见,S. baltica XH2为冷藏大黄鱼的SSO,其强致腐能力与torA基因高表达量和TorA蛋白理化性质有关。研究为阐明希瓦氏菌致腐机制奠定了良好的基础。

Preliminary mechanism of different spoilage potential of specific spoilage organism,Shewanella,in refrigerated Larimichthys crocea

To evaluate the mechanism of difference spoilage potential of the specific spoilage organism (SSO), Shewanella, H2S-producing bacteria isolated from the refrigerated large yellow croaker were identified using the physicochemical reactions and 16s rDNA. Four strains with differences spoilage potential were selected in the sterile fish juice and fish block. The gene and expression of trimethylamine oxidation (TMAO) reductase in four strains were amplified and determined, and physicochemical properties of the protein were predicted. The results showed that all H2S-producing bacteria were identified to Shewanella, in which S. baltica, S. putrefaciens and S.hafniensis accounted for 54.5%, 40.9% and 4.5%, respectively. Significant differences of the spoilage potential were in fish juice among Shewanella observed. The sensory score and TVB-N content of isolates S. baltica XH2 and XH8 were significantly higher than other strains (p< 0.05), whereas the indicators of isolates S. putrefaciens XH14 and XH17 were the lowest. The sample inoculated S. baltica XH2 was found to produce off-odors after 72h, higher than 107 cfu/g of TVC after 48h, strong reduction ability of TMAO to TMA, high accumulation of TVB-N, cadaverine and putrescin, followed by S. baltica XH8, S. putrefaciens XH14 and XH17. The 2490 bp fragment of torA gene were amplified in four Shewanella isolates. Expression of torA gene of four isolates was correlated with the spoilage potential, in which S.baltica XH2 exhibited the highest expression. Furthermore, the biggest molecular weight and aliphatic index of predicted TorA protein were observed, whereas theoretical pI and gravy were the lowest in S.baltica XH2. Thus, SSO in chilled large yellow croaker was S. baltica XH2, and the high spoilage potential in the isolate was associated with high level of torA expression and some physicochemical properties of TorA protein. It will provide a good foundation to clarify the mechanism of spoilage in Shewanella.