Isolation and characterisation of purple non-sulfur bacteria from aquaculture ponds in Ninh Binh and evaluation of their sulfide-removal capacity under laboratory conditions

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, to identify strains with high sulfide-removal potential for improving water quality, enhancing productivity, and reducing the risk of disease outbreaks in aquaculture ponds. A total of 17 PNSB strains were isolated, among which strains ND2 and NH6 exhibited the highest sulfide removal efficiency (>96%) at 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 as the NaCl concentration increased to 3-5%. Both strains maintained high sulfide removal efficiency in media containing 2-3% NaCl, reaching 97.48% for ND2 and 96.40% for NH6 at 2% NaCl. However, removal efficiency decreased at 4-5% NaCl, with values of 86.79 and 84.84% for ND2 and NH6, respectively, at 5% NaCl. Strain ND2 exhibited better growth and sulfide removal than strain NH6 at NaCl concentrations of 4-5% and was selected for molecular identification as Rhodovulum sulfidophilum. These findings suggest that R. sulfidophilum ND2 has strong potential for efficient sulfide removal in aquaculture water.