Inoculation with arsenic-oxidizing and -reducing bacteria enhances arsenic uptake, speciation, and phytoremediation efficiency in <i>Pteris vittata</i>

The arsenic hyperaccumulator <i>Pteris vittata</i> is a prime candidate for phytoremediating globally concerning soil arsenic pollution, however, the mechanism by which arsenic-transforming bacteria enhance its efficiency remains unelucidated. This study used a rhizobag soil culture method to compare the impacts of arsenic-oxidizing (Agrobacterium sp.) and -reducing bacterial (Delftia sp.) strains on arsenic absorption, transformation, and root exudation in <i>P. vittata</i>. The results showed that inoculation of the two microorganisms boosts <i>P. vittata</i>'s arsenic uptake: frond and root arsenic contents are 1.57-2.87 and 1.22-2.09 times that of the non-inoculated group, and arsenate-reducing bacteria exert a more significant effect. Arsenic-reducing bacteria raised As(III) proportions in the fern and soil, while arsenic-oxidizing bacteria increased As(V) in the fern. Microbial inoculation also promoted root secretion of oxalic, malic, and acetic acids, more significantly at 5 d than 30 d. In conclusion, exogenous microorganisms improve the fern's arsenic absorption and soil remediation efficiency, offering a microbial strategy for optimizing arsenic phytoremediation.