Photosynthetic bacteria enhanced water quality and integrity of microbial community composition of integrated multitrophic aquaculture system of milkfish Chanos chanos coastal farming

Aquaculture faces substantial challenges in mitigating the detrimental environmental impacts of intensive farming. Traditional methods have given rise to serious concerns, leading to the search for alternative approaches using probiotics. An indigenously isolated photosynthetic purple bacterium, Rhodovulum sulfidophilum, was introduced into a marine integrated multitrophic aquaculture system cultivating Chanos chanos in southwestern Taiwan. The effects of R. sulfidophilum on water quality parameters, the relative levels of nitrogenase-encoding nifH and nitrous oxide reductase-encoding nosZ genes, the occurrence of sulfonamide resistance, the presence of sulfonamide resistance genes, and microbial community structure were determined. Supplementation with R. sulfidophilum decreased the chemical oxygen demand, the nitrate levels, and the occurrence of sulfonamide-resistant bacteria in the fishpond water compared with that of the control after rearing. The level of the sulfonamide resistance gene sul2 decreased in R. sulfidophilum-supplemented water samples, while the control exhibited an elevated level of sul2 after rearing. Supplementation with R. sulfidophilum also maintained the integrity of the bacterial community structure. In conclusion, our results suggest that R. sulfidophilum is an attractive supplement for enhanced disease emergence control, microbial biodiversity maintenance, and sustainable marine aquaculture practice.