Characterization of an arsenite-oxidizing caballeronia sp. soil bacterium and its mutualistic relationship with trifolium pratense for arsenic remediation

Abstract

The proposed application of the mutualistic interaction between a native arsenicoxidizing soil bacteria and Trifolium pratense in Northwestern Ontario mine sites is a novel approach to remediation. This thesis studies the characteristics of an arsenic-oxidizing bacterium isolated from a gold mine in Hemlo, Ontario; observes the variance in arsenic (As) toxicity to three different plant species commonly used as phytoremediators; and analyzes the interaction of one of these three plant species with the isolated soil bacterium. The conversion of trivalent inorganic As(III) to its pentavalent form (As(V)) is a widely accepted detoxification pathway. By enriching soil samples collected from the mine’s tailing areas with 1 mM sodium arsenite (As(III)) mineral salt solution, 125 As-tolerant soil bacteria were isolated. Silver nitrate (AgNO3) screening and subsequent ICP-AES analysis determined that isolate LU-71 was the only As-oxidizer. An As(III)-induced LU-71 culture had a 74±19% conversion efficiency of As(III) to As(V) in 18 h. The isolate was identified as a novel As-oxidizer in the Caballeronia genus by 16S rDNA sequencing and the bacterium also had the ability to produce siderophores. The Asoxidizing bacteria experienced optimal growth at 25°C and pH 7, and was determined to be a heterotroph with a minimum inhibitory concentrations of As(III) and As(V) of 8 and 200 mM, respectively. The LD50 of As(III) was 11 times less than As(V) to the germination of T. pratense, F. rubra, and M. sativa seeds. The LD50 of As(III) to seeds inoculated with the As-oxidizing bacteria was about 6 times greater than the LD50 of As(III) to uninoculated seeds. To T. pratense plant growth and biomass production, the As-oxidizing bacteria increased yield by 43%. Given its success promoting plant germination and growth in As-stressed environments, the As-oxidizing Caballeronia bacteria is a potentially cost-effective remediation approach to mines in Ontario.