Effect of rice bran fermented with Bacillus and Lysinibacillus species on dynamic microbial activity of Pacific white shrimp (Penaeus vannamei)

Abstract

This study aimed to evaluate the effect of rice bran fermented with a consortium of Bacillus and Lysinibacillus strains (RB + BLb) on the bacterial community structure and composition in the gastrointestinal tract of Pacific white shrimp (Penaeus vannamei), as well as its effect on growth performance and health status. Rice bran fermented with a commercial probiotic (RB + Com) was also evaluated for comparative purposes. Rice bran with or without probiotics, pre-fermented for 24 h, was directly added to the rearing water of juvenile shrimp for 4 weeks. At the end of the experimental period, shrimp treated with RB + BLb had a slightly better shrimp growth performance and survival than the control group; however, the differences were not statistically significant (p > 0.05) among treatments. Moreover, histological analyses showed that shrimp treated with RB + BLb improved the nutritional status compared to other treatments, by inducing an increase in lipid reserves of hepatopancreas epithelial cells. The analysis of the bacterial community composition revealed that the most prevalent families were Rhodobacteraceae, Vibrionaceae and Flavobacteriaceae. Although sequences affiliated to the Rhodobacteraceae family were more abundant in shrimp treated RB + Com, a lower proportion of sequences affiliated to the Vibrionaceae family was found in shrimp treated with unfermented rice bran (RB) or RB + Com, when compared with the control group or those treated with RB + BLb. The abundance of sequences affiliated to the Flavobacteriaceae family was significantly lower in shrimp treated with RB + BLb or RB + Com than the control group or those treated with RB.These results could explain, in part, the mechanisms of action whereby the use of rice bran fermented with a consortium of probiotic bacteria confer beneficial effects on shrimp culture.