Project description:Cunner (Tautogolabrus adspersus) is a cleaner fish being considered for utilized in the North Atlantic salmon (Salmo salar) 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 Pseudomonas 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, Pseudomonas sp. J380 produced pyoverdine-type fluorescent siderophore. Koch's postulates were verified in wild cunners by intraperitoneally (i.p.) injecting Pseudomonas sp. J380 at 4 × 103, 4 × 105, and 4 × 107 colony forming units (CFU)/dose. Host-range and comparative virulence were also investigated in lumpfish and Atlantic salmon i.p. injected with ~106 CFU/dose. Lumpfish were more susceptible compared to cunners, and Atlantic salmon was resistant to Pseudomonas sp. J380 infection. Cunner tissues were heavily colonized by Pseudomonas sp. J380 compared to lumpfish and Atlantic salmon suggesting that it might be an opportunistic pathogen in cunners. The genome of Pseudomonas 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 Pseudomonas sp. J380 belongs to the P. fluorescens 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, Pseudomonas sp. J380.
Project description:The intestinal microbiota is involved in a wide range of biological processes that benefit the host, including providing nutrition and modulating the immune system. Fine flounder (Paralichthys adspersus) is a flatfish of commercial interest that is native to the Chilean coast. The high value of this flatfish has prompted the development of stock enhancement and aquaculture activities. Knowledge of microbiota may help to improve the cultivation of this species; however, few comparative studies have evaluated the intestinal microbiota composition in farmed versus wild fishes. Intestinal contents from wild and aquaculture fish were collected, and DNA was extracted. Subsequently, the V3-region of 16S rRNA was PCR amplified and sequenced using the Ion Torrent platform. The comparison between wild and aquaculture specimens revealed important differences in the composition of the microbiota. The most abundant phylum in wild flounder was Proteobacteria, with an average relative abundance of 68.1 ± 15.4%; in contrast, in aquaculture flounder, this phylum had an average relative abundance of 30.8 ± 24.1%. Reciprocally, the most abundant phylum in flounder aquaculture was Firmicutes, averaging 61.2 ± 28.4%; in contrast, this phylum showed low abundance in wild flounder, in which it averaged 4.7 ± 4%. The phylum Actinobacteria showed greater abundance in wild flounder, ranging from 21.7 ± 18.8%, whereas, it averaged only 2.7 ± 3.8% in aquaculture fish. Specific taxa that were differentially distributed between wild and aquaculture flounder were identified using a statistical approach. At the genus level, a total of four genera were differentially represented between the two conditions. Bacillus and Pseudomonas were more highly represented in aquaculture flounder, whereas Arthrobacter and Psychrobacter were observed in wild flounder. Furthermore, in both cases, predicted functions (metabolic pathways) indicated that those microbiota might provide beneficial effects for the host, but wild flounder showed more noteworthy pathways (EPA/DHA, SCFA, biotin). Our results highlight the differences in the microbiota composition between wild and reared fish. Knowing the composition of the intestinal microbiota of P. adspersus is the first step toward exploring the proper management of this species, as well as toward the development of probiotics and functional foods based on their requirements.