The potential of acid-resistant purple nonsulfur bacteria isolated from acid sulfate soils for reducing toxicity of Al3+ and Fe2+ using biosorption for agricultural application

This research aimed to investigate the status of Al3+ and Fe2+ distribution in wetland rice on acid sulfate soil (ASS) in Southern Thailand and Mekong Delta, Vietnam; to isolate and select the H+, Al3+ and Fe2+ -resistant purple nonsulfur bacteria (PNSB) from ASS and to evaluate biosorption of selected PNSB to reduce both metals. Soil pHKCl value was below 5.0 in all surveyed sites; while the pH value of water samples ranged from 4.73 to 7.77. The highest concentrations of both cations in both samples types were detected in Mekong Delta as in water samples were 12.42 mg Al3+ L−1 and 48.04 mg Fe2+ L−1 in the areas of Tan Phuoc and Thap Muoi, Plain of Reed. For soil samples, the maximal concentration of both cations were 142.87 mg Al3+ kg−1 with 68.06 mg Fe2+ kg−1 in Hon Dat, Long Xuyen Quadrangle area, and 501.22 mg Fe2+ kg−1 with 26.83 mg Al3+ kg−1 in Phung Hiep, Depressed of Hau River area. Six PNSB that resisted to strong acid with the critical doses of 68 mg Al3+ L−1 and 250 mg Fe2+ L−1 for rice were selected from 101 PNSB. Strains TLS06, TLW99, VNW64, VNW02 and VNS89 were identified as Rhodopseudomonas spp.; while strain VNW29 was Rhodobacter sp. Strain VNW64 was the most effective to remove Al3+, Fe2+ and both mixture ions by biosorption in various pH values (4.0-5.0). It would be possible to apply the selected PNSB in acidic paddy fields for reducing the toxicity of Al3+ and Fe2+.