Marine protease-producing bacterium and its potential use as an abalone probiont

Gastrointestinal tracts (GITs) of aquatic animals were considered as ideal sources for isolating aquaculture probiotic candidates. Thus, this study aimed to isolate protease-producing bacteria from GITs of hybrid abalone (Haliotis rubra x Haliotis laevigata), and screened them for their potential uses as abalone probionts. Ten proteolytic bacterial strains were isolated, and all isolates phenotypically referred to genus Bacillus. Among the 10 pure strains, MA228 had the highest ability to hydrolize casein and gelatine. Through 16S rRNA sequence (accession number MG976611), the isolate showed 99% similarity to Bacillus amyloliquefaciens. Further in vitro assays indicated that the bacterial strain had good viability and stability in manufactured pellets stored at 4 °C, seawater with a salinity of 35 mg/L, and simulated gastrointestinal tract conditions of abalone. Additionally, another in vitro study indicated that protease produced by the probiotic candidate could significantly hydrolase protein content in manufacture pellet of abalone. These results suggest that B. amyloliquefaciens MA228 is a potential probiont for increasing protein digestibility in hybrid abalone.