Enhanced degradation of isoproturon in an agricultural soil by a Sphingomonas sp. strain and a microbial consortium

Abstract

Isoproturon (IPU) degradation in an agricultural soil inoculated with an isolated IPU-degrader strain (Sphingomonas sp. strain AK1, IS) or a microbial consortium (MC) harboring this strain, with or without carrier material, were investigated in soil microcosm experiments during 46 days. Effect of the carrier material and inoculation size on IPU-degradation efficacy of the inoculants were studied. Mineralization, extractable residues and non-extractable residues of 14C-labeled IPU were analyzed. The low IPU mineralization in untreated soil (7.0%) was enhanced to different extents by inoculation of IS (17.4%–46.0%) or MC (58.9%–67.5%). Concentrations of IPU residues in soils amended with MC (0.002–0.095 μg g dry soil−1) were significantly lower than in soils amended with IS (0.02–0.67 μg g dry soil−1) and approximately 10 times lower than in the uninoculated soil (0.06–0.80 μg g dry soil−1). Less extractable residues and non-extractable residues were detected in soil with higher IPU mineralization. Inoculation size (as indicated by the volume of liquid cultures or by the number of carrier particles) determined the IPU-removal efficacy of IS in soil, but this effect was less pronounced for MC. The low sorption of IPU to soil and the decreasing IPU-mineralizing rates suggested incapability of IS to establish the IPU-mineralizing function in the soil. The thorough removal of IPU and persistent IPU-mineralizing activity of soil inoculated with MC indicated a high persistence of IPU-metabolic trait. Our results showed that microbial consortia might be more efficient than single degrader strains to enhance clean-up of organic chemicals in soil.