Aims: The gut microbiota is referred to an extra organ and is ciritical in assisting the host in terms of nutrition and immunity. Environmental stressors could alter gut microbial community and cause gut inflammation. This study aimed to investigate and compare the gut microbiota community between healthy and diseased Tor tambroides. Methodology and results: In this study, such gut microbial alterations were explored using NGS-based 16S rDNA sequencing on the Malaysian mahseer (T. tambroides). Three adult healthy and three diseased adult Malaysian mahseers (showing signs of exophthalmia, coelomic distension and petechial haemorrhage) were obtained from LTT Aquaculture Sdn Bhd. Our results revealed significant differences in microbial diversity, composition and function between both populations of T. tambroides. Alpha diversity analysis depicts lower diversity of gut microbiota composition in diseased T. tambroides as compared to the healthy group. In particular, Enterobacteriaceae, Aeromonas, Bacteroides, Vibrio and Pseudomonas were found within gut microbiota of the diseased fishes. In addition, cellulose-degrading bacteria and protease-producing bacteria were identified from the gut of T. tambroides. Conclusion, significance and impact of study: Thus, our findings emphasised on the association between the alteration in gut microbiota composition and infectious abdominal dropsy (IAD) in T. tambroides. This finding is important to provide basic information for further diagnosis, prevention and treatment of intestinal diseases in fish.

BackgroundPseudomonas koreensis have been reported as a pathogen in freshwater fish. Unlike environmental P. koreensis from soil, which has been studied extensively for its role in promoting plant growth, pathogenic P. koreensis from fish has been assessed only to a very limited extent. This is the first draft genome of P. koreensis CM-01 isolated from the internal organs of diseased Tor tambroides.ResultsHerein, we report the morphological and biochemical characteristics, as well as whole genome sequences of a newly identified P. koreensis strain. We achieved a high-quality draft genome of P. koreensis CM-01 with a N50 value of 233,601 bp and 99.5% BUSCO completeness. The total size of P. koreensis CM-01 genome contains 6,171,880 bp and has a G+C content of 60.5%. Besides, the genome sequence includes 5538 protein-coding genes, 3 rRNA genes, 54 tRNAs, and no plasmids were found. Besides these, 39 interspersed repeat and 141 tandem repeat sequences, 6 prophages, 51 genomic islands, 94 insertion sequences, 4 clustered regularly interspaced short palindromic repeats, 5 antibiotic-resistant genes, and 150 virulence genes were predicted in the P. koreensis CM-01 genome. In addition, the assembled CM-01 genome was successfully annotated against the Cluster of Orthologous Groups of proteins database, Gene Ontology database, and Kyoto Encyclopedia of Genes and Genome pathway database. A comparative analysis of CM-01 with three representative strains of P. koreensis revealed that 92% of orthologous clusters were conserved among these four genomes, and only the CM-01 strain possesses unique elements related to pathogenicity and virulence.ConclusionsThis study provides fundamental phenotypic and genomic information for the newly identified P. koreensis strain. Further study will be necessary to fully understand any correlation between the bacteria and the occurrences of diseases in Tor tambroides.

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