Anaerobic degradation of toluene and xylene by aquifer microorganisms under sulfate-reducing conditions

TLDR

The study used a mixed culture derived from gasoline‑contaminated aquifer sediment at Seal Beach, California, to investigate anaerobic degradation of toluene and xylene under sulfate‑reducing conditions. The culture completely mineralized toluene and all xylene isomers to CO₂ and biomass, with >90 % of ¹⁴C‑labelled substrates converted, sulfate serving as the terminal electron acceptor, while benzene and ethylbenzene remained resistant; successive transfers preserved this activity, the culture doubled every ~20 days with a cell yield of 0.1–0.14 g dry weight per g substrate, and sulfide accumulation from sulfate reduction inhibited further aromatic degradation.

Abstract

Toluene and the three isomers of xylene were completely mineralized to CO2 and biomass by aquifer-derived microorganisms under strictly anaerobic conditions. The source of the inoculum was gasoline-contaminated sediment from Seal Beach, Calif. Evidence confirming that sulfate was the terminal electron acceptor is presented. Benzene and ethylbenzene were not degraded under the experimental conditions used. Successive transfers of the mixed cultures that were enriched from aquifer sediments retained the ability to degrade toluene and xylenes. Greater than 90% of 14C-labeled toluene or 14C-labeled o-xylene was mineralized to 14CO2. The doubling time for the culture grown on toluene or m-xylene was about 20 days, and the cell yield was about 0.1 to 0.14 g of cells (dry weight) per g of substrate. The accumulation of sulfide in the cultures as a result of sulfate reduction appeared to inhibit degradation of aromatic hydrocarbons.