Isolation of arsenite-oxidizing bacteria with plant growth promoting characteristics to enhance phytoremediation of arsenic

Abstract

A common strategy for remediation of arsenic is bacterial remediation by oxidation of As(III) to the less toxic As(V). Another widely accepted technique for arsenic remediation is phytoremediation however in highly contaminated soil, growth of the plants is stunted. Phytoremediation of arsenic is often assisted with plant growth promoting bacteria to improve plant growth. However, there are only a handful of studies on bacteria that can oxidize arsenite as well as promoting plant growth, much less on the implications that they can improve the growth of phytoremediating plants in arsenic contaminated soil. In this study, a group of plant growth promoting arsenite-oxidizing bacteria (PGP As(III)-oxidizing bacteria) from the root zone of plants established in the tailing of the Premier Gold Mine, Beardmore, Ontario was isolated and characterized and their ability to promote the growth of Trifolium pratense (red clover) in arsenite contaminated condition was investigated. Thirty-four arsenic resistant bacteria were isolated from the soil collected at the tailing site that was highly contaminated with arsenic (1208 ± 582 ug/g). The isolates were tested both qualitatively and quantitatively for their arsenite-oxidizing ability by using the silver nitrate test and the APDC/ICP-AES analysis, respectively, and all of them demonstrated the ability to oxidize arsenite. The isolates were identified by 16S rDNA sequencing, and a phylogenetic tree was constructed using the maximum likelihood method. The 34 isolates were highly diverse including six different genera. The isolates were tested for four different plant growth promoting characteristics: (i) phosphate solubilization, (ii) siderophore production, (iii) IAA (indole-3-acetic acid) production and (iv) presence of ACC (1-aminocyclopropane-1- carboxylic acid) deaminase. [...]