Specific prebiotics improved growth, pathogen inhibition and short-chain fatty acids production by probiotic bacilli: Screening synbiotic combinations for aquaculture

This study aimed to assess the effect of three commercially available prebiotics (fructooligosaccharide, inulin, and pectin) on the growth of six potential probiotics belonging to the Bacillus species ( Bacillus licheniformis , B. methylotrophicus , B. altitudinis , B. amyloliquefaciens , B. safensis , and B. tequilensis ), and test the performance of their synbiotic combinations. The study also assessed their antagonistic activity against aeromonad fish pathogens and the production of short-chain fatty acids (SCFA). Optical density measurements at 600 nm revealed that four of the Bacillus spp. utilized tested prebiotics as the carbon source. The maximum growth of B. licheniformis and B. methylotrophicus were noticed with fructooligosaccharide (FOS) and inulin, respectively. However, both B. safensis and B. amyloliquefaciens grew well in the presence of pectin. Cell-free supernatant from B. methylotrophicus grown with inulin exhibited significant antagonism against Aeromonas hydrophila , while A. salmonicida and A. veronii were effectively inhibited by the metabolites from B. licheniformis grown with FOS. Additionally, B. safensis grown in pectin-supplemented media demonstrated inhibition against A. sobria . Antibacterial substances produced by the probiotic strains were stable across a broad pH range (4–9) and resistant to heat (up to 90°C), although partial loss of activity was noticed after treatment with trypsin and proteinase-K, suggesting its proteinaceous nature. Among the SCFAs, substantial acetate production was detected by the four Bacillus spp., being significantly higher with B. methylotrophicus grown in inulin compared to the others. Furthermore, considerable amounts of butyrate and propionate were produced by both B. licheniformis with FOS and B. methylotrophicus in inulin medium. These findings underscore the importance of specific probiotic-prebiotic interactions ( B. licheniformis + FOS, B. methylotrophicus + inulin, B. safensis + pectin, and B. amyloliquefaciens + pectin) in synbiotic development suggesting likely application of these formulations to promote health benefits in aquaculture. • Selective utilization of prebiotics by probiotic bacilli indicated potential for synbiotic development. • B. licheniformis with FOS, B. methylotrophicus with inulin, B. safensis / B. amyloliquefaciens with pectin showed utmost growth. • Antagonism against Aeromonas spp. was heightened when probiotic strains were grown with their preferred prebiotics. • Proteinaceous antibacterials produced by synbiotic combinations demonstrated stability across various temperatures and pH. • High SCFA production (acetate, butyrate, and propionate) was detected in specific probiotic-prebiotic combinations.