Characterization of Bacillus subtilis from gastrointestinal tract of hybrid Hulong grouper (Epinephelus fuscoguttatus × E. lanceolatus) and its effects as probiotic additives

Fish Shellfish Immunol. 2019 Jan:84:1115-1124. doi: 10.1016/j.fsi.2018.10.058. Epub 2018 Oct 26.

Abstract

Probiotics are widely used for the improvement of animals' growth and health. However, few marine aquatic probiotics are applied and licensed in China. In this study, a Bacillus spp. strain was isolated from the Hulong grouper gastrointestinal tract, which was identified as a new strain of Bacillus subtilis and was named as 7k. B. subtilis 7k showed desirable capability of sporulation and resistance to heat, simulated gastric juice and simulated duodenum juice, indicating its potential as probiotics. Seven antimicrobial chemicals were found in the secretion of the B. subtilis 7k. B. subtilis 7k addition in diet promoted the growth rate of Hulong groupers. Moreover, B. subtilis 7k can inhibit infection by iridovirus, making B. subtilis 7k a suitable kind of probiotic for maintaining fishes' health. Our results also revealed that B. subtilis 7k induced non-specific immune response in Hulong grouper under virus infection. Hulong grouper fed by diets containing B. subtilis 7k at 108 and 1010 cfu g-1 for 4-8 weeks were significantly strengthened in serum lysozyme activity, serum alternative complement activity (ACH50), serum bactericidal activity, respiratory burst, superoxide dismutase activity (SOD), and phagocytic activity of head kidney leucocytes when compared with those fed by control diets. In conclusion, B. subtilis 7k was isolated and characterized to be a kind of process enduring, growth stimulating, immunity enhancing and health promoting probiotic using in grouper culture.

Keywords: Bacillus subtilis; Grouper; Growth; Innate immunity; Probiotic.

MeSH terms

  • Aeromonas hydrophila / physiology
  • Animal Feed / analysis
  • Animals
  • Bacillus subtilis / chemistry*
  • Bass / genetics
  • Bass / immunology*
  • DNA Virus Infections / prevention & control
  • DNA Virus Infections / veterinary*
  • DNA Virus Infections / virology
  • Diet / veterinary
  • Fish Diseases / prevention & control*
  • Fish Diseases / virology
  • Gastrointestinal Tract / microbiology
  • Hybridization, Genetic
  • Immunity, Innate / drug effects*
  • Micrococcus / physiology
  • Probiotics / chemistry
  • Probiotics / pharmacology*
  • Ranavirus / physiology
  • Staphylococcus aureus / physiology
  • Vibrio / physiology