Fishpond microbiota, their synergism with fish and potential biotechnological applications

Samenvatting

The present study verified in-vitro, the capabilities of microbes isolated from pond water (PW), pond carp gut flush (FG), and homogenized pond carp gut (HG) to digest cellulose, protein, phytate, and starch. Followed by safety assessment (antibiotics resistance and haemolytic test), suppression of fish pathogenic bacteria, taxonomy (phylogenetic analysis), and resilience (growth potential under adverse environmental conditions) of the microbial isolates for potential biotechnological applications. Out of the n = 28 morphologically distinct microbial isolates assayed, majority (19 (67.9 %)) could hydrolyse at least one of the tested substrates. PW samples overall had highest functional diversity in hydrolysing all the substrates we assayed, but the intensity of hydrolysis was highest in a HG sub-variant associated with Bacillus tequilensis (also present in pond water, but presumably better performance of gut colony). Antimicrobial assessment showed all the selected isolates can inhibit the growth of pathogenic Aeromonas salmonicida associated with diseases in fish. Other valuable characteristics of the selected isolates include survival at low pH (4–6) and resistance to high temperatures (up to 80–90 °C). The 16S and ITS rDNA gene sequence and phylogenetic analysis showed that the selected isolates belong to the genera Bacillus, Aspergillus, and Pseudomonas. Results suggest 8 potent multipurpose microbes from fishponds for possible use in degradation of complex biopolymers of non-refined feedstuff (fermentation), probiotics, and sources of valuable enzymes for aquafeed industry. Some isolates demonstrated beta haemolysis under low oxygen conditions. In vivo haematological studies are needed in the future to confirm the safety of promising microbial isolates.