Isolation of Bacillus subtilis and Bacillus pumilus with Anti-Vibrio parahaemolyticus Activity and Identification of the Anti-Vibrio parahaemolyticus Substance

The adoption of intensive farming has exacerbated disease outbreaks in aquaculture, particularly vibriosis caused by Vibrio parahaemolyticus. The use of probiotics to control V. parahaemolyticus is recognized as a good alternative to antibiotics for avoiding the development of antibiotic-resistant bacteria. In this study, two strains of B. HLJ1 and B. C1 with strong inhibitory activity on V. parahaemolyticus were isolated from aquaculture water and identified as Bacillus subtilis and Bacillus pumilus, respectively. Both B. HLJ1 and B. C1 lacked antibiotic resistance and virulence genes, suggesting that they are safe for use in aquaculture. In addition, these two strains can tolerate acid environments, produce spores, secrete extracellular enzymes, and co-aggregate as well as auto-aggregate with V. parahaemolyticus. B. HLJ1 and B. C1 produced the same anti-V. parahaemolyticus substance, which was identified as AI-77-F and belongs to amicoumacins. Both B. C1 and B. HLJ1 showed inhibitory activity against 11 different V. parahaemolyticus and could effectively control the growth of V. parahaemolyticus in simulated aquaculture wastewater when the concentration of B. C1 and B. HLJ1 reached 1 x 10(7) CFU/mL. This study shows that B. HLJ1 and B. C1 have great potential as aquaculture probiotics.

Automated summary

The study isolated and identified two strains of bacteria, B. HLJ1 and B. C1, from aquaculture water that exhibited strong inhibitory activity against V. parahaemolyticus. These strains, identified as Bacillus subtilis and Bacillus pumilus respectively, lacked antibiotic resistance and virulence genes, making them safe for use in aquaculture. B. HLJ1 and B. C1 demonstrated the ability to tolerate acidic conditions, produce spores, secrete extracellular enzymes, and co-aggregate with V. parahaemolyticus. Both strains produced AI-77-F, an anti-V. parahaemolyticus substance belonging to amicoumacins, and effectively controlled the growth of V. parahaemolyticus in simulated aquaculture wastewater.