Evaluation of the Probiotic Potential of Bacillus spp. Strains Isolated from River Bottom Sediments

The study aimed to evaluate bottom sediments as a promising source of probiotic bacteria for aquaculture applications. Bacillus strains were selected as the most suitable bacterial species for application in the food industry. Initially, seven Bacillus spp. strains were isolated from the intestinal contents of healthy sterlet specimens; however, none of them demonstrated high potential probiotic properties. Subsequently, bottom sediments were considered as a source of probiotic strains. In the bottom sediments, bacilli exist in a vegetative form and constitute an integral part of the microbial community. A total of 120 Bacillus spp. strains were isolated and comprehensively analyzed. Proteolytic and amylolytic activities were detected at moderate levels in almost all isolated strains. Most isolates exhibited low or negligible antioxidant, DNA-protective, and antimicrobial activities; however, a small group of strains showed high values of these properties. Principal component and cluster analyses indicated the co-existence of three life strategies of bacilli in bottom sediments. These findings highlight the high probiotic potential of bacilli from bottom sediments and support their suitability as novel probiotics for enhancing the health and productivity of aquatic organisms in aquaculture.