Shu Feng-Ling, Jin Li-Yun, Liu Hao, Tao Zhen, Yin Fei, Xie Jia-Song, Zhou Su-Ming
Key Laboratory of the Ministry of Education for Applied Marine Biotechnology, School of Marine Science, Ningbo University, Ningbo, China.
School of Fisheries, Zhejiang Ocean University, Zhoushan, Zhejiang Province, China.
J Fish Dis. 2023 Mar;46(3):229-238. doi: 10.1111/jfd.13737. Epub 2022 Dec 9.
Pseudomonas plecoglossicida is an important pathogenic bacterium in aquaculture that causes visceral granulomas in large yellow croaker (Larimichthys crocea). Uridine diphosphate glucose phosphorylase encoded by galU plays a key role in biosynthesis of the bacterial envelope, particularly lipopolysaccharide and the capsule. In this study, we inactivated the galU gene in the P. plecoglossicida isolate XSDHY-P. The galU mutant strain showed impaired growth in the early exponential stage and lacked the O polysaccharide side chain in lipopolysaccharide, but almost no defect in biofilm formation was detected. The galU mutant strain also exhibited significantly more sensitivity to the bactericidal action of normal fish serum mediated by the complement system compared to the wild-type strain. In a cell model originating from the head kidney of large yellow croaker, the galU mutant strain showed lower capacities of adhesion, invasion, and intracellular survival compared to the wild-type strain. In addition, the deficiency of the galU mutant drastically decreased bacterial loads in tissues and attenuated P. plecoglossicida virulence in fish. These results suggest that the galU gene of P. plecoglossicida is required for in vivo survival in large yellow croaker.
嗜水气单胞菌是水产养殖中的一种重要病原菌，可导致大黄鱼（Larimichthys crocea）出现内脏肉芽肿。由galU编码的尿苷二磷酸葡萄糖磷酸化酶在细菌包膜的生物合成中起关键作用，特别是在脂多糖和荚膜的生物合成中。在本研究中，我们使嗜水气单胞菌分离株XSDHY-P中的galU基因失活。galU突变株在指数生长早期生长受损，脂多糖中缺乏O多糖侧链，但未检测到生物膜形成有明显缺陷。与野生型菌株相比，galU突变株对补体系统介导的正常鱼血清杀菌作用也表现出明显更高的敏感性。在源自大黄鱼头肾的细胞模型中，与野生型菌株相比，galU突变株表现出较低的粘附、侵袭和细胞内存活能力。此外，galU突变株的缺陷显著降低了组织中的细菌载量，并减弱了嗜水气单胞菌在鱼体内的毒力。这些结果表明，嗜水气单胞菌的galU基因是大黄鱼体内生存所必需的。
