Sun Jiakai, Su Haochen, Zhang Wenhui, Luo Xuesong, Li Ruichao, Liu Ming
College of Oceanography, Hohai University, Nanjing, China.
Jiangsu Co-Innovation Center for Prevention and Control of Important Animal Infectious Diseases and Zoonoses, College of Veterinary Medicine, Yangzhou University, Yangzhou, China.
Arch Microbiol. 2023 Apr 26;205(5):207. doi: 10.1007/s00203-023-03557-1.
The type VI secretion system (T6SS) is important for interbacterial competition and virulence in Vibrio species. It is generally agreed that T6SS provides a fitness advantage to Vibrios. Some Vibrio species possess one, while others possess two T6SSs. Even within the same Vibrio species, different strains can harbor a variable number of T6SSs. Such is the case in V. fluvialis, an opportunistic human pathogen, that some V. fluvialis strains do not harbor T6SS1. This study found that Amphritea, Marinomonas, Marinobacterium, Vibrio, Photobacterium, and Oceanospirillum species have genes encoding V. fluvialis T6SS1 homologs. The cladogram of T6SS1 genes suggested that these genes appeared to be horizontally acquired by V. fluvialis, V. furnissii, and some other Vibrio species, when compared with the species tree. Codon insertions, codon deletions, nonsense mutations, and the insertion sequence are found in many genes, such as clpV1, tssL1, and tssF1, which encode structure components of T6SS1 in V. furnissii and V. fluvialis. Codon deletion events are more common than codon insertion, insertion sequence disruption, and nonsense mutation events in genes that encode components of T6SS1. Similarly, codon insertions and codon deletions are found in genes relevant to T6SS2, including tssM2, vgrG2 and vasH, in V. furnissii and V. fluvialis. These mutations are likely to disable the functions of T6SSs. Our findings indicate that T6SS may have a fitness disadvantage in V. furnissii and V. fluvialis, and the loss of function in T6SS may help these Vibrio species to survive under certain conditions.
VI型分泌系统（T6SS）对于弧菌属细菌之间的竞争和毒力至关重要。人们普遍认为T6SS为弧菌提供了适应性优势。一些弧菌属细菌拥有一个T6SS，而其他弧菌则拥有两个T6SS。即使在同一弧菌属细菌中，不同菌株所含T6SS的数量也可能不同。河流弧菌作为一种机会性人类病原体就是如此，一些河流弧菌菌株不携带T6SS1。本研究发现，两栖菌属、海单胞菌属、海杆菌属、弧菌属、发光杆菌属和海洋螺菌属的细菌拥有编码河流弧菌T6SS1同源物的基因。T6SS1基因的系统发育树表明，与物种树相比，这些基因似乎是河流弧菌、弗氏弧菌和其他一些弧菌属细菌通过水平基因转移获得的。在许多基因中发现了密码子插入、密码子缺失、无义突变和插入序列，例如在弗氏弧菌和河流弧菌中编码T6SS1结构成分的clpV1、tssL1和tssF1基因。在编码T6SS1成分的基因中，密码子缺失事件比密码子插入、插入序列破坏和无义突变事件更为常见。同样，在弗氏弧菌和河流弧菌中，与T6SS2相关的基因（包括tssM2、vgrG2和vasH）中也发现了密码子插入和密码子缺失。这些突变可能会使T6SS的功能丧失。我们的研究结果表明，T6SS在弗氏弧菌和河流弧菌中可能具有适应性劣势，T6SS功能的丧失可能有助于这些弧菌属细菌在某些条件下生存。
