Substrate‐ and nutrient‐limited toluene biotransformation in sandy soil

Abstract

Lab microcosm tests of the rate of toluene biodegradation were performed using soil from the A, B, and C horizons of the unsaturated zone of a sandy field site. Most of the soil samples had been previously exposed to toluene. Toluene biodegradation was rapid, occurring at a time scale comparable to the rate of sorption in many of the microcosms and demonstrating the potential for bioremediation of these contaminants in unsaturated soil. In the A horizon, with an initial toluene concentration in the solution phase of 4.5 mg/L, degradation was controlled by substrate-limited growth on toluene as the primary substrate. Soil from the B and C horizons initially showed similar behavior with a lower toluene concentration of about 2.5 mg/L.The maximum utilization rate (pmax) for soil from all three depths was 2.0 d-' . With repeated exposure to moderate to high concentrations of toluene, transformation in the B-and C-horizon soil appeared to be zero order, at a rate of 1 .O to 2.0 pg toluene/g soil/d. In C-horizon soil that had been taken directly from the field, the transformation rate was almost immeasurably slow. Addition of nitrogen as either ammonium or nitrate accelerated the degradation, showing that nitrogen was the most limiting nutrient.The apparent adaptation period observed before rapid toluene removal was fit by a substrate-limited growth model. Greater numbers of toluene-degrading microorganisms were found in soil exposed to toluene than in unexposed soil, supporting biomass growth as the explanation for the adaptation period. The results of enumeration of heterotrophs compared to the numbers of toluene degraders suggested that a small proportion of the total viable microorganisms were responsible for degradation of toluene.

Microbial community response to petroleum hydrocarbon contamination in the unsaturated zone at the experimental field site Værløse, Denmark

“…Batch experiments carried out with Værløse soil showed increasing degradation when ammonium vapor was added (N. Dakhel and P. Höhener, personal communication), which confirms the assumption of N‐limitation. This finding is in agreement with the better correlation of cell numbers with N tot than with any other soil parameter ( R 2 >0.9) and is concordant with results of [41], who found N limitation for toluene degradation in subsurface soils.…”

Microbial community response to petroleum hydrocarbon contamination in the unsaturated zone at the experimental field site V�rl�se, Denmark

“…Batch experiments carried out with Vrløse soil showed increasing degradation when ammonium vapor was added (N. Dakhel and P. H€ ohener, personal communication), which confirms the assumption of N-limitation. This finding is in agreement with the better correlation of cell numbers with N tot than with any other soil parameter (R 2 > 0:9) and is concordant with results of [41], who found N limitation for toluene degradation in subsurface soils.…”

Catabolite repression of the toluene degradation pathway in Pseudomonas putida harboring pWW0 under various conditions of nutrient limitation in chemostat culture

“…From the environmental point of view, these results are not particularly relevant since maximal growth rate conditions do not, in general, occur under field conditions. In soil and surface water, the degradation of xenobiotics is often limited by the available concentration of oxygen (4, 6), phosphate (16,24,28), or nitrogen (2,16). We mimicked these limiting conditions in chemostat cultures of P. putida(pWW0) growing on a succinate-mineral medium and studied the inducibility of the TOL pathway in response to the nonmetabolizable inducer o-xylene.…”