Effect of Native Bacillus Strains Supplemented in Water on Growth Performance, Resistance to Vibrio parahaemolyticus (AHPND strain), and Gut Microbiota of White Shrimp (Penaeus vannamei)
Authors: Maliwan Kutako, Janjarus Wattanachote, Thannari Tharanat, Kamonchanok Sriprat, Kongka Kongwised, Chaddanai Chaihan and Molruedee SonthiSource: Shrimp sediment pond, Chanthaburi shrimp farmBacillus as a probiotic in shrimp has been widely studied, but the efficacy and properties are strain-specific, thus suitable strains from local aquaculture sources should be selected. Indigenous strains are usually better and more specific as they have been co-adapted with the host and the environment. It has been reported that strains isolated from aquatic animals or their culture environment colonize faster and are more stable, robust and persistent. The host immune system tends to respond less vigorously against them because they are already part of the resident microbiota. In an earlier study of our research group, Bacillus strains were isolated from the bottom sediment of shrimp culture ponds and B. subtilis and B. cereus were found to exhibit remarkable characteristics including rapid growth, high spore production and strong capacity to degrade total organic carbon (TOC) in shrimp rearing water. On the other hand, their efficacy has yet to be tested in a real shrimp culture system. The aquatic microbial community is the main source of microorganisms entering the shrimp intestine, due to the constant contact with rearing water and ingestion of the water during feeding. Filter-feeding behavior facilitates acquisition of resident gut microbiota with waterborne bacteria, resulting in a constant microbial exchange between rearing water and digestive tract. Thus, manipulation of the water microbiome represents a promising strategy for regulating gut microbial composition. Direct application of probiotics to rearing water may operate through two complementary mechanisms. Probiotic bacteria can contribute to organic matter degradation and improved pond water quality, and their continuous presence in the water can facilitate entry of beneficial microorganisms into the shrimp digestive tract, thereby supporting a favorable gut microbial community and stronger resistance to disease. Feed-based and water-based probiotic applications have both been investigated, though knowledge of water-based or immersion applications in relation to intestinal Bacillus abundance and disease resistance is comparatively limited relative to dietary supplementation. In response to the research gap, the present study evaluated the effects of adding isolated Bacillus subtilis and Bacillus cereus strains directly to rearing water on the growth performance, resistance to Vibrio parahaemolyticus (VPAHPND), and gut bacterial community composition of P. vannamei. Findings from the study may strengthen understanding of water-applied probiotics as a practical strategy for promoting shrimp health and supporting more sustainable shrimp production.