Comparison of the probiotic effects of freshwater and marine photosynthetic bacteria in kuruma shrimp (Marsupenaeus japonicus) culture

In a field study, the probiotic effects of a freshwater purple nonsulfur photosynthetic bacterium (PNSB), Rhodobacter sphaeroides, and a marine PNSB, Rhodovulum sulfidophilum, on kuruma shrimp (Marsupenaeus japonicus) were compared by using two commercially operating shrimp ponds. Shrimp were fed with feed containing 0.01% fresh weight (10(6) cfu/g feed) of PNSB cells for 152 d. The marine PNSB showed a better performance than the freshwater PNSB in average body weight at harvest time, survival rate (P < 0.001 by Fisher's exact test), and feed conversion rate. The effects of freshwater and marine PNSB on shrimp gene expression were also compared by next-generation sequencing and quantitative RT-PCR. Both freshwater and marine PNSB promoted the expression of several genes related to the innate immune system, including NADPH oxidase, superoxide dismutase, lysozyme, antimicrobial peptides, and lectins, and the promotive effect of marine PNSB was stronger than that of freshwater PNSB. The cost of PNSB was calculated to be US$ 0.003-0.005 per kg feed; thus, marine PNSB is a cost-effective and feasible probiotic for shrimp aquaculture.