Purple nonsulfur bacteria (PNSB) can potentially improve rice growth, grain yield and soil fertility in acid sulfate
soils (ASS) by acting as biofertilizers and bioremediators. Six strains of acid resistant PNSB (Rhodopseudomonas
palustris; TLS12, VNS19, VNS32, VNS62 and VNW95, and Rhodopseudomonas harwoodiae TLW42) were evaluated,
as single cultures and a mixed culture of the six strains, for their effects on rice growth and soil fertility in
ASS with high Mn concentrations sampled at three sites in the Mekong Delta, Vietnam. In pot experiments, all
single PNSB strains in the liquid biofertilizer, especially strain VNS32, significantly improved most plant growth
parameters, rice yield, and soil fertility. They increased NH4+ and available phosphorus (Pavail) but reduced Mn2+
compared with the controls in all three soils. In pot experiments, the solid PNSB biofertilizers significantly
improved rice growth and grain yield, reduced accumulated Mn and increased soil fertility. The solid formula of
six mixed strains was the most effective, followed by VNS32 singly, and lastly the carrier control with no added
PNSB. In the field trials, the solid mixed PNSB biofertilizer combined with 75% NP fertilizer significantly
enhanced rice growth, producing the same grain yields as 100% NP fertilizer at two of the sites, and a higher
yield at one of the sites. In acidic paddy fields, acid resistant PNSB can act as biofertilizers and bioremediators to
produce improvements in soil fertility and healthier rice crops.