一株鳢源鰤诺卡氏菌致病性与全基因组分析

Pathogenicity and whole genome analysis of a Nocardia seriolae strain isolated from snakehead

摘要:

【背景】鰤诺卡氏菌是一种典型的条件致病菌，感染鳢、鲈等多种名优鱼类，易造成存在机体损伤或免疫机能下降的鱼持续性感染，给水产养殖业造成了巨大损失。【目的】了解临床分离鳢源鰤诺卡氏菌对乌斑杂交鳢(斑鳢♀×乌鳢♂)的致病性，并从全基因组层面了解该病原菌的基因组和致病因子信息，为鰤诺卡氏菌后续病原学及鰤诺卡氏菌病防治技术和疫苗的开发研究提供有利的数据支撑。【方法】鰤诺卡氏菌NK201610020通过回归感染试验和发病鱼靶器官组织病理分析，了解鰤诺卡氏菌的毒力和病理特征。通过对试验菌进行全基因组测序和比较基因组学分析，挖掘该菌的基因组与毒力特征。【结果】回归感染试验结果显示，除1.5×10³组外，其余5个感染组致死率高达90%，LD₅₀为1.079×10³ CFU/mL，说明试验菌毒力较强。组织病理学观察到肝、脾、肾呈现严重的病理损伤，而且有肉芽肿结构形成。试验菌全基因组测序发现，全基因组大小为8 294 329 bp，GC含量为68.10%，共预测到编码基因7 812个。比较基因组学分析发现，不同地区不同宿主来源鰤诺卡氏菌在基因组基础特征层面无明显差异，而且一致性在99.9%以上。通过毒力基因数据库比对，预测试验菌全基因组中有171个编码序列可能为毒力基因，其功能主要与细胞壁合成、营养代谢、细菌持续感染相关。【结论】鰤诺卡氏菌毒力强，基因组序列保守，携带多种毒力因子，研究结果为进一步研究鰤诺卡氏菌的致病机制提供了有利的数据支撑。

Abstract:

[Background] The infection of Nocardia seriolae, a typical opportunistic pathogen, has been documented in many kinds of fishes such as Channa argus and Micropterus salmoides, particularly wounded fishes or fishes with decreased immunity. The resulted nocardiosis lasts a long time, causing great loss to the aquaculture. [Objective] This paper aims to clarify the pathogenicity of Nocardia seriolae isolated from hybrid snakehead (C. maculata♀×C. argus♂), as well as the whole genome and virulence factors information of the pathogen, which is expected to lay a basis for the future research on etiology ofNocardia seriolae, prevention and control of this pathogen, and vaccine development. [Methods] Through challenge test and pathological analysis of target snakehead organs, the virulence and pathogenic characteristics of Nocardia seriolae NK201610020 were elucidated. In addition, based on whole-genome sequencing and comparative genomics analysis, the genomic features and virulence genes information of the strain were clarified. [Results] The result of challenge test showed that the death rates in the five infection groups were up to over 90% except the group of 1.5×10³, and the LD₅₀is1.079×10³ CFU/mL, which indicating the strong virulence of the strain. Histopathological results revealed serious pathological damages in liver, spleen, and kidney, as well as formation of granulomas. The whole genome of NK201610020 was 8 294 329 bp with GC content of 68.10% and 7 812 coding genes. The genomes of Nocardia seriolae from different hosts and different regions showed little difference (>99.9% similarity). According to the alignment with virulence gene database, 171 coding genes in the genome of NK201610020 might be virulence genes, which were involved in cell wall synthesis, nutrient metabolism, and persistent bacterial infection. [Conclusion] Nocardia seriolae has strong virulence, and conserved genome sequence containing diverse virulence genes. The results lay a basis for further analysis of Nocardia seriolae pathogenic mechanism.