牛肉源热杀索丝菌的致腐差异和比较基因组学研究

Spoilage Difference and Comparative Genomics Studies on the Brochothrix thermosphactafrom Beef

为探究牛肉中热杀索丝菌的致腐能力和致腐基因分布特点,经分离纯化、形态观察和PCR鉴定,获得29株热杀索丝菌。将其接种于4℃牛肉汁中,测定挥发性盐基氮(TVB-N)值和乙偶姻指标,评价分离菌株的致腐能力。采用比较基因组学技术分析热杀索丝菌强、弱腐败株基因特点。结果表明,29株热杀索丝菌分离株的TVB-N含量形成较慢,仅有2株菌在第9天超过11.5 mg N/100 g,而产乙偶姻能力强,且有明显差异,其中菌株BT27和BT25含量分别为139.3μg/mL和59.5μg/mL。测定强、弱致腐菌株BT27和BT25的全基因组序列,结果发现,热杀索丝菌基因组中存在大量参与碳水化合物代谢的基因,其中编码糖苷水解酶的基因数量最多,糖基转移酶基因次之。比较基因组学显示,强致腐株BT27被注释到碳水化合物代谢和相应酶的编码基因数量均多于弱致腐株BT25,而两者在编码氨基酸代谢的基因数量相近。研究表明,热杀索丝菌致腐性强、弱与编码碳水化合物代谢基因数量密切相关,研究从基因层面为阐明肉源微生物的致腐机理奠定了良好的基础。

In order to explore the spoilage ability and gene characteristics of Brochothrix thermosphacta in beef,29 strains were obtained by purification,morphological observation and PCR identification from chilled beef.The spoilage potential of these isolates was evaluated by the production of total volatile basic nitrogen(TVB-N)and acetoin index in beef juice at 4℃.The whole genome sequences of strong and weak spoilers were compared.The results showed that the TVB-N values increased slowly,and only two strains exceeded 11.5 mg N/100 g on the 9th day.In contrast,these isolates strongly produced acetoin,and their producing abilities differed.The acetoin contents of strain BT27 and BT25 were 139.3μg/mL and 59.5μg/mL,respectively.The whole genome sequencing of BT27 and BT25 showed a large number of genes involved in carbohydrate metabolism,the largest number of genes was encoding glycoside hydrolase,followed by glycosyltransferase genes.Comparative genomics showed that the number of genes encoding carbohydrate metabolism and corresponding enzymes of strong spoiler BT27 was more than that of weak spoiler BT25,while the number of genes encoding amino acid metabolism was similar between them.This study indicated that the spoilage ability of B.thermosphacta was correlated to the number of genes encoding carbohydrate metabolism,which provided the genetic point of view for elucidating the spoilage mechanism of meat microbiology.