Analysis of the ability of Channa striatus gut-derived Lactococcus garvieae bacteria to reach and persist in the gut environment along with extracellular metabolites and its behavior against common fish pathogens

Exploration of gut microbiota is a resource for researchers to study the range and role of micro-organisms. Exploring gut microbiota of fishes that survive in harsh environmental conditions, catches eye that opportunity of finding new strain may be more. The present study was undertaken to explore the gastrointestinal tract of adult Channa striatus collected from Doaba region of Punjab. A total of 34 isolates were isolated and screened for antimicrobial activity against fish pathogens: Aeromonas hydrophila and Pseudomonas aeruginosa. Four of these isolates were Gram positive. Of these four isolates, only one isolate PMS1 showed good antimicrobial activity against the Aeromonas hydrophila. The isolate exhibited high tolerance to low pH and strong adhesion capability. The isolate was found susceptible to all tested antibiotics. Based on in vitro assessment, biochemical and 16srRNA analysis the strain was identified as Lactococcus garvieae. Furthermore, extracellular metabolites were isolated and analyzed through Gas Chromatography-Mass Spectrometry technique. The results revealed the presence of two compounds (1, 3, 5, 7, 9, 11- Hexaethylcyclohexasiloxane and 2, 6 Lutidine 3, 5 dichloro-4- dodecylthio-). This study concludes that the isolate showed positive in vitro results and the metabolites do not confirm the pathogenicity of the strain. The findings suggest that further studies are required to evaluate the effect of Lactococcus garvieae PMS1 in fish.