Aerobic biodegradation of natural and xenobiotic organic compounds by subsurface microbial communities

Abstract

AbstractStudies were conducted to characterize the diversity of degradative abilities of microbial communities from pristine aquifer solids samples. Biodegradation was measured in aquifer solids slurries as both the conversion of radiolabeled substrate to 14CO2 and the incorporation of label into cell biomass. Under aerobic conditions, the microbial community metabolized the following naturally occurring compounds: acetic acid, amino acids, cellulose, cinnamic acid, glucosamine and glucose. The xenobiotic compounds aniline hydrochloride, chlorobenzene, p‐chloro‐phenol, m‐cresol, ethylene dibromide, naphthalene, phenol, toluene and trichlorobenzene were also biodegraded. Several kinetic parameters were calculated from the uptake and mineralization data. First‐order rate constants (K1) ranged from 10−2 to 10−4 h−1 for the natural compounds and from 10−3 to 10−6 h−1 for the xenobiotic compounds. Turnover times ranged from 47 to more than 1,900 h for natural compounds and from 806 to 60,000 h for xenobiotic compounds. For some compounds, respiratory enzymes became saturated, whereas incorporation into biomass was first‐order. The results show that uptake into cell biomass represents a large fraction of total metabolism for many of the xenobiotic compounds. 14C‐most‐probable‐number (MPN) of substrate degraders was calculated. MPNs for naturally occurring compounds ranged from 102 to 106 per gram of soil. There were generally fewer than 10 xenobiotic degraders per gram of soil. The biodegradative activity of the subsurface community appears to differ in both rate and product distribution from the activities of aquatic or surface‐soil communities.