Evaluating the Impact of Arsenic on Enzyme Activity in Soil.

Arsenic (As) occurs naturally in the soil, rocks and minerals. However this background concentration is being increased to toxic levels through anthropogenic activities—agricultural activities (animal waste, pesticides), mining, industrial waste, etc. Arsenic is toxic to most known soil microbes, which are critical to the maintenance of the soil’s ecosystem functions, such as nutrients cycling. Little is known about the impact of arsenic on fungi and microbial structure and nutrient cycling enzymes produced by these soil organisms. Understanding this impact will enable better agricultural practices, and use in remediation to restore contaminated soil. In this study, the effect of different concentrations (1, 5, and 10 ppm) of As(III) and As(V) on fungi community structure and nutrients cycling enzymes: acid phosphomonoesterase, phosphodiestersae, and β-Glucosidase;   were evaluated. Total genomic DNA was extracted from each treatment and subjected to PCR and pyrosequencing analysis and operational taxonomic units were defined after removal of singleton sequences. Taxonomic classification was done using BLASTn against a curated GreenGenes database and compiled into “counts” and “percentage” files. Chytridiomycota, Chlorophyta, and Alveolata all were observed to have a tolerance of arsenic at 1 ppm, but became more sensitive at levels 5 ppm and 10 ppm. Ascomycota declined initially at an arsenic level of 1 ppm, but gradually increased as the arsenic levels increased. The phylum groups, Proteobacteria was the largest classified phyla accounting for about 50% of the total number of groups. Actinobacteria growth were most inhibited by the arsenic treatments with the least population observed in 10 ppm As(III). The enzymes assayed in this study show that biochemical functions were reduced in the presence of As, as well as impact the bacteria community structure. In general, phosphomonoesterase, phosphodiestersae, and β-Glucosidase were inhibited by both As(III) and As(V), however the 5 ppm As(III) enhanced the activity of β-Glucosidase.