Research has validated the effects of probiotics on growth, immunity, and pathogen inhibition. We are interested in further elucidating the inhibitory characteristics of probiotics against Vibrio species, and in the process, we will need to understand Vibrios. We have observed that bacteria from the same species can have different potencies against shrimp pathogens. Inhibition of pathogens has been attributed to quorum quenching, lipopeptides, antibiotics, bacteriocins, and biofilm formation, and an effective probiotic can improve water quality.
Probiotics for Aquaculture usually consist of four Bacillus species: subtilis, licheniformis, pumilus, and amyloliquefaciens. These bacteria contribute to the product’s efficacy in different ways. Since not all species have the same abilities, we would like to define our products to the best of our ability to reach our goal of producing designer products that will be the most effective for each situation.
In this study, to accomplish a competitive approach, we included several different Vibrio and Bacillus species, including strains of each species. Proteins from culture supernatants and cell-derived proteins were used in inhibition studies against Vibrio species. We ranked our probiotics based on the % reduction in growth of the Vibrios. The comparison of the results from the supernatant proteins and cell-derived proteins was insightful and will be discussed. Quorum-sensing studies were performed, and PCR was used to identify quorum quenching (QQ) genes in Bacillus. Highlights from the results showed that QQ is inducible; some strains of B. subtilis and B. pumilus, and V. vulnificus had a lactonase that quenched C6-homoserine lactones, whereas the amyloliquefaciens strains did not. We analyzed enzyme activity and the presence of lipopetide genes across the Bacillus species, and the data and discussion of the results will be presented.