Bacterial ability in AsIII oxidation and AsV reduction: Relation to arsenic tolerance, P uptake, and siderophore production.

The relationship between bacterial ability in arsenic transformation, siderophore production, and P uptake was investigated using six arsenic-resistant bacteria isolated from the rhizosphere of arsenic-hyperaccumulator Pteris vittata. Bacterial strains of PG5 and 12 were better arsenite (AsIII) oxidizers (31-46 vs. 6.2-21% of 1 mM AsIII) whereas PG 6, 9, 10 and 16 were better arsenate (AsV) reducers (58-95 vs. 7.5-46% of 1 mM AsV). Increase in AsV concentration from 0 to 1 mM induced 3.0-8.4 times more P uptake by bacteria but increase in P concentration from 0.1 to 1 mM reduced AsV uptake by 17-71%, indicating that P and AsV were taken up by P transporters. Bacteria producing more siderophores (PG5 and 12; >73 μM equiv) showed greater AsIII oxidation and AsIII resistance than those producing less siderophore (PG 6, 9, 10 and 16; <23 μM equiv). This observation was further supported by results obtained from mutants of Pseudomonas fluorescens impaired in siderophore production, as they were 23-25% less tolerant to AsIII than the wild-type. Arsenic-resistant bacteria increased their arsenic tolerance by retaining less arsenic in cells via efficient AsIII oxidation and AsV reduction, which were impacted by P uptake and siderophore production.