Isolation and characterisation of purple non-sulfur bacteria for sulfide removal in aquaculture ponds of Vietnam

Abstract

This study aimed to isolate and select purple non-sulfur bacteria (PNSB) strains from 10 water and 15 sediment samples collected from various aquaculture ponds in Ninh Binh province, Vietnam, with the potential to remove sulfide from water, thereby contributing to improving water quality, enhancing productivity, and reducing the risk of disease outbreaks in aquaculture systems. A total of 17 PNSB strains were successfully isolated, among which strains ND2 and NH6 exhibited the highest sulfide removal efficiency (>96%) under sulfide concentrations of 10-20 mg/l. Both strains showed optimal growth at 2% NaCl, with OD_660nm values of 1.03 and 1.15, respectively, and their growth decreased at higher salinities (3-5% NaCl). Sulfide removal efficiency remained high in media containing 2-3% NaCl, achieving 97.48% for ND2 and 96.40% for NH6 at 2% NaCl. However, efficiency decreased at 4-5% NaCl, with ND2 and NH6 showing 86.79% and 84.84% removal at 5% NaCl, respectively. Notably, strain ND2 exhibited superior growth and sulfide degradation capability under high salinity (2-5% NaCl) and was identified by molecular analysis as Rhodovulum sulfidophilum. These findings suggest that Rhodovulum sulfidophilum ND2 is a promising candidate for application in sulfide remediation and water quality improvement in aquaculture systems.