Beneficial effects of a host gut-derived probiotic, Bacillus pumilus, on the growth, non-specific immune response and disease resistance of juvenile golden pompano, Trachinotus ovatus

A potential host-derived probiotic, Bacillus pumilus A97, was successfully screened from 434 isolates from the intestines of healthy adult Trachinotus ovatus based on in vitro assays of non-haemolytic activity, extracellular enzyme activity, inhibitory activity against pathogens (Vibrio or Streptococcus), tolerance to gastrointestinal stress and bile salts, cell surface hydrophobicity, autoaggregation, biofilm formation and antibiotic susceptibility. Dietary supplementation with B. pumilus A97 (1.0 x 10(8) CFU.g(-1)) for 56 days significantly improved the weight gain, specific growth rate, feed efficiency and non-specific immune responses of T. ovatus (P < .05). The mRNA levels of toll-like receptor 8 (TLR8) in the intestines and toll-like receptor 9 (TLR9) in the kidneys of T. ovatus were significantly upregulated (P < .05). Higher survival rates post- Vibrio ponticus-challenge was found in T. ovatus fed an A97 diet than in the control fish. All the results suggest that B. pumilus A97 has great potential as an effective dietary probiotic for improving the growth, immune status and disease resistance of T. ovatus.