Occurrence of drugs in German sewage treatment plants and rivers

Dissimilatory Sulfate- and Sulfur-Reducing Prokaryotes

The focus of this review is to examine some of the reasons biodegradation may not take place in the environment even though its occurrence in the laboratory has been demonstrated. Some approaches for dealing with chemical persistence will be discussed. In addition, the potential of bioremediation as an in situ clean-up technology will be considered.

Selected factors limiting the microbial degradation of recalcitrant compounds

Mononuclear aromatic compounds are degraded anaerobically through three main pathways, the benzoyl-CoA pathway, the resorcinol pathway, and the phloroglucinol pathway. Various modification reactions channel a broad variety of mononuclear aromatics including aromatic hydrocarbons into either one of these three pathways. Recently, a further pathway was discovered with hydroxyhydroquinone as central intermediate through which especially nitrate-reducing bacteria degrade phenolic compounds and some hydroxylated benzoates. Comparison of the various strategies taken for the degradation of aromatics in the absence of oxygen demonstrates that the biochemistry of breakdown of these compounds is determined largely by the overall reaction energetics and, more precisely, by the redox potentials of the electron acceptor systems used. Nitrate reducers differ in their strategies significantly from those used by sulfate-reducing or fermenting bacteria.

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Anaerobic degradation of phenolic compounds.

In situ biodegradation potential of aromatic hydrocarbons in anaerobic groundwaters

Sulfate-reducing bacterial enrichments were obtained from a shallow anoxic aquifer for their ability to metabolize eithero-, m-, orp-cresol. GC/MS and simultaneous adaptation experiments suggested that the anaerobic decomposition ofp-cresol proceeds by the initial oxidation of the aryl methyl group to formp-hydroxybenzoic acid. This intermediate was then converted to benzoic acid. Benzoic acid and a hydroxybenzaldehyde were also found in spent culture fluids from ano-cresol-degrading enrichment culture. This result, in addition to others, suggested thato-cresol may also be anaerobically degraded by the oxidation of the methyl substituent. An alternate pathway for anaerobicm-cresol decomposition might exist. Enrichment cultures obtained with eitherp- oro-cresol degraded both of these substrates but notm-cresol. In contrast, am-cresol enrichment culture did not metabolize theortho orpara isomers. Anaerobic biodegradation in all enrichment cultures was inhibited by molybdate and oxygen, and was dependent on the presence of sulfate as a terminal electron acceptor. The stoichiometry of sulfate-reduction and substrate depletion by the various enrichment cultures indicated that the parent cresol isomers were completely mineralized. This result was confirmed by the conversion of14C-labeledp-cresol to14CO2. These results help clarify the fate of alkylated aromatic chemicals in anoxic aquifers.

The anaerobic biodegradation of o-, m- and p-cresol by sulfate-reducing bacterial enrichment cultures obtained from a shallow anoxic aquifer

spectral analysis, we foundthata haloaromatic dehalogenating consortium, a dehalogenating isolate fromthatconsortium, Eubacterium limosum, anda strain ofAcetobacterium woodii metabolized 3-[methoxy-'80]methoxybenzoic acid(3-anisic acid) to3-[hydroxy-180]hydroxybenzoicstoichiometrically atratesof1.5,3.2,52.4, and36.7nmol/min per mg ofprotein, respectively. A different strain ofAcetobacterium andstrains ofSyntrophococcus, Clostridium, Desulfotomaculum, Enterobacter, andan anaerobic bacterium, strain TH-001, were unable to transform thiscompound. The0-demethylating ability ofE.limosum was induced onlywithappropriate methoxylated benzoates butnotwithD-glucose, lactate, isoleucine, ormethanol. Cross-acclimation andgrowth experiments withE.limosum showed a rateofmetabolism that was anorder ofmagnitude slower andshowed no growthwitheither 4-methoxysalicylic acid(2-hydroxy-4-methoxybenzoic acid) or 4-anisic acid(4methoxybenzoic acid) whenadapted to3-anisic acid. However, A.woodii NZva-16 showedslower ratesandno growthwith3-or 4-methoxysalicylic acidwhenadapted to3-anisic acidinsimilar experiments. Theresults clearly indicate a methyl rather thanmethoxy group removal mechanism forsuchreactions.

Adesh Saxena

Papers

The anaerobic biodegradation of o-, m- and p-cresol by sulfate-reducing bacterial enrichment cultures obtained from a shallow anoxic aquifer

Metabolism ofthe'80-Methoxy Substituent of3-Methoxybenzoic AcidandOtherUnlabeled Methoxybenzoic Acidsby Anaerobic Bacteria