Umasuthan Navaneethaiyer, Valderrama Katherinne, Vasquez Ignacio, Segovia Cristopher, Hossain Ahmed, Cao Trung, Gnanagobal Hajarooba, Monk Jennifer, Boyce Danny, Santander Javier
Marine Microbial Pathogenesis and Vaccinology Laboratory, Department of Ocean Sciences, Memorial University of Newfoundland, St. John's, NL A1C 5S7, Canada.
Dr. Joe Brown Aquatic Research Building (JBARB), Department of Ocean Sciences, Memorial University of Newfoundland, Logy Bay, NL A1C 5S7, Canada.
Microorganisms. 2021 Apr 12;9(4):812. doi: 10.3390/microorganisms9040812.
Cunner () is a cleaner fish being considered for utilized in the North Atlantic salmon () aquaculture industry to biocontrol sea lice infestations. However, bacterial diseases due to natural infections in wild cunners have yet to be described. This study reports the isolation of sp. J380 from infected wild cunners and its phenotypic, genomic, and transcriptomic characterization. This Gram-negative motile rod-shaped bacterium showed a mesophilic (4-28 °C) and halotolerant growth. Under iron-limited conditions, sp. J380 produced pyoverdine-type fluorescent siderophore. Koch's postulates were verified in wild cunners by intraperitoneally (i.p.) injecting sp. J380 at 4 × 10, 4 × 10, and 4 × 10 colony forming units (CFU)/dose. Host-range and comparative virulence were also investigated in lumpfish and Atlantic salmon i.p. injected with ~10 CFU/dose. Lumpfish were more susceptible compared to cunners, and Atlantic salmon was resistant to sp. J380 infection. Cunner tissues were heavily colonized by sp. J380 compared to lumpfish and Atlantic salmon suggesting that it might be an opportunistic pathogen in cunners. The genome of sp. J380 was 6.26 megabases (Mb) with a guanine-cytosine (GC) content of 59.7%. Biochemical profiles, as well as comparative and phylogenomic analyses, suggested that sp. J380 belongs to the species complex. Transcriptome profiling under iron-limited vs. iron-enriched conditions identified 1159 differentially expressed genes (DEGs). Cellular metabolic processes, such as ribosomal and energy production, and protein synthesis, were impeded by iron limitation. In contrast, genes involved in environmental adaptation mechanisms including two-component systems, histidine catabolism, and redox balance were transcriptionally up-regulated. Furthermore, iron limitation triggered the differential expression of genes encoding proteins associated with iron homeostasis. As the first report on a bacterial infection in cunners, the current study provides an overview of a new marine pathogen, sp. J380.
康氏躄鱼（Cunner）是一种清洁鱼，正被考虑用于北大西洋鲑鱼（Atlantic salmon）水产养殖业，以生物防治海虱侵扰。然而，野生康氏躄鱼因自然感染导致的细菌性疾病尚未见报道。本研究报告了从受感染的野生康氏躄鱼中分离出J380菌株，并对其进行了表型、基因组和转录组特征分析。这种革兰氏阴性、具运动性的杆状细菌表现出嗜温（4-28℃）和耐盐生长特性。在铁限制条件下，J380菌株产生了吡嗪型荧光铁载体。通过腹腔注射（i.p.）4×10⁶、4×10⁷和4×10⁸菌落形成单位（CFU）/剂量的J380菌株，在野生康氏躄鱼中验证了科赫法则。还对腹腔注射约10⁶CFU/剂量的七鳃鳗和大西洋鲑进行了宿主范围和比较毒力研究。与康氏躄鱼相比，七鳃鳗更易感染，而大西洋鲑对J380菌株感染具有抗性。与七鳃鳗和大西洋鲑相比，康氏躄鱼组织被J380菌株大量定殖，这表明它可能是康氏躄鱼中的一种机会致病菌。J380菌株的基因组为6.26兆碱基（Mb），鸟嘌呤-胞嘧啶（GC）含量为59.7%。生化特征以及比较和系统基因组分析表明，J380菌株属于鲭鱼弧菌（Vibrio anguillarum）物种复合体。在铁限制与铁丰富条件下的转录组分析确定了1159个差异表达基因（DEGs）。铁限制阻碍了核糖体和能量产生以及蛋白质合成等细胞代谢过程。相反，参与环境适应机制的基因，包括双组分系统、组氨酸分解代谢和氧化还原平衡，在转录水平上上调。此外，铁限制引发了与铁稳态相关蛋白质编码基因的差异表达。作为关于康氏躄鱼细菌感染的首次报告，本研究概述了一种新的海洋病原体——J380菌株。
