Marine Mugil cephalus gut-derived Pseudomonas stutzeri GM30 from : A Novel Probiotic and Amylase-Based Postbiotic for Sustainable Aquaculture

Asian aquaculture faces growing threats from biofilm-forming bacterial pathogens, compounded by widespread antimicrobial resistance from antibiotic overuse. This study explores host-derived probiotics as viable alternatives by isolating gut bacteria from Mugil cephalus, a key marine fish species cultured along India's southeastern coast. Among 28 isolates recovered from intestinal contents, strain GM30 showed promising antimicrobial and enzymatic properties. Molecular identification using 16S rRNA gene sequencing confirmed it as Pseudomonas stutzeri, showing 99% similarity Using agar well diffusion assays, GM30 demonstrated inhibitory activity against six common fish pathogens, including Aeromonas salmonicida, Aeromonas caviae, Vibrio harveyi, Vibrio vulnificus, Edwardsiella tarda, and Staphylococcus aureus. The strain exhibited favourable probiotic characteristics: 37.1% surface hydrophobicity, indicating high adhesion potential; 3% tolerance to bile salts; 70.5% autoaggregation capacity after 24 hours; and 29.03% antioxidant activity via DPPH radical scavenging. GM30 produced several digestive enzymes: amylase (0.68 U/mL), pectinase (0.93 U/mL), protease, lipase, and cellulase, which could improve nutrient utilisation and feed conversion efficiency in commercial settings. Interestingly, the partially purified amylase fraction (50-65 kDa) showed activity beyond simple starch breakdown. It appeared to disrupt the polysaccharide structures within pathogenic biofilms, suggesting an additional protective mechanism against persistent infections. This combination of pathogen inhibition, enzyme production, gastrointestinal stress tolerance, and potential biofilm disruption makes P. stutzeri GM30 worth investigating further for practical aquaculture applications. The results support developing antibiotic-free strategies that address both productivity enhancement and disease management challenges in intensive fish farming systems prevalent across Asia.