Microbial degradation of toluene under sulfate-reducing conditions and the influence of iron on the process

Abstract

Toluene degradation occurred concomitantly with sulfate reduction in anaerobic microcosms inoculated with contaminated subsurface soil from an aviation fuel storage facility near the Patuxent River (Md.). Similar results were obtained for enrichment cultures in which toluene was the sole carbon source. Several lines of evidence suggest that toluene degradation was directly coupled to sulfate reduction in Patuxent River microcosms and enrichment cultures: (i) the two processes were synchronous and highly correlated, (ii) the observed stoichiometric ratios of moles of sulfate consumed per mole of toluene consumed were consistent with the theoretical ratio for the oxidation of toluene to CO2 coupled with the reduction of sulfate to hydrogen sulfide, and (iii) toluene degradation ceased when sulfate was depleted, and conversely, sulfate reduction ceased when toluene was depleted. Mineralization of toluene was confirmed in experiments with [ring-U-14C]toluene. The addition of millimolar concentrations of amorphous Fe(OH)3 to Patuxent River microcosms and enrichment cultures either greatly facilitated the onset of toluene degradation or accelerated the rate once degradation had begun. In iron-amended microcosms and enrichment cultures, ferric iron reduction proceeded concurrently with toluene degradation and sulfate reduction. Stoichiometric data and other observations indicate that ferric iron reduction was not directly coupled to toluene oxidation but was a secondary, presumably abiotic, reaction between ferric iron and biogenic hydrogen sulfide.

Degradation of the cyanobacterial hepatotoxin microcystin by aquatic bacteria

“…The absence of a lag phase upon re-addition of microcystin LR to water samples was also consistent with other biodegradation studies [Beller et al, 1992;Holliger et al, 19921 and supports the contention that a degradatively competent population is selected or induced during the lag phase. These results suggest that biodegradation may commence more rapidly in water bodies that have frequent exposure to microcystin-producing cyanobacterial blooms.…”

Anaerobic Metabolism of Aromatic Compounds

“…The pathway of benzylsuccinate oxidation to benzoyl-CoA has not yet been elucidated. Whole cell suspensions of different toluene-grown denitrifying and sulfate-reducing strains are known to convert varying amounts of toluene to benzylsuccinate and derivatives thereof (Evans et al, 1992;Beller et al, 1992;Seyfried et al, 1994;Rabus and Widdel, 1995a;Chee-Sanford et al, 1996;Migaud et al, 1996). This intermediate accumulation in the medium may be best ascribed to variable amounts of cell lysis in the experiments, since none of the toluene-degrading strains so far studied can degrade exogenous benzylsuccinate.…”

An anaerobic field injection experiment in a landfill leachate plume, Grindsted, Denmark: 2. Deduction of anaerobic (methanogenic, sulfate‐, and Fe (III)‐reducing) redox conditions

“…Different redox processes may be linked since, for example, abiotic Fe(III) reduction from biologically produced sulfide has been observed by Beller et al [1992]. Such a linkage could confound the interpretation of Fe(II) production as a biological Fe(III) reduction where in fact the biological process is sulfate reduction.…”