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Biomedical subjects

S E Herbes

Publications and source records attributed to S E Herbes.

7 recordsLinked to original sources
PubMed1990

Biodegradation of trichloroethylene in continuous-recycle expanded-bed bioreactors.

Experimental bioreactors operated as recirculated closed systems were inoculated with bacterial cultures that utilized methane, propane, and tryptone-yeast extract as aerobic carbon and energy sources and degraded trichloroethylene (TCE). Up to 95% removal of TCE was observed after 5 days of incubation. Uninoculated bioreactors inhibited with 0.5% Formalin and 0.2% sodium azide retained greater than 95% of their TCE after 20 days. Each bioreactor consisted of an expanded-bed column through which the liquid phase was recirculated and a gas recharge column which allowed direct headspace sampling. Pulses of TCE (20 mg/liter) were added to bioreactors, and gas chromatography was used to monitor TCE, propane, methane, and carbon dioxide. Pulsed feeding of methane and propane with air resulted in 1 mol of TCE degraded per 55 mol of substrate utilized. Perturbation studies revealed that pH shifts from 7.2 to 7.5 decreased TCE degradation by 85%. The bioreactors recovered to baseline activities within 1 day after the pH returned to neutrality.

Journal Article↗
PubMed1988

Trichloroethylene biodegradation by a methane-oxidizing bacterium.

Trichloroethylene (TCE), a common groundwater contaminant, is a suspected carcinogen that is highly resistant to aerobic biodegradation. An aerobic, methane-oxidizing bacterium was isolated that degrades TCE in pure culture at concentrations commonly observed in contaminated groundwater. Strain 46-1, a type I methanotrophic bacterium, degraded TCE if grown on methane or methanol, producing CO(2) and water-soluble products. Gas chromatography and C radiotracer techniques were used to determine the rate, methane dependence, and mechanism of TCE biodegradation. TCE biodegradation by strain 46-1 appears to be a cometabolic process that occurs when the organism is actively metabolizing a suitable growth substrate such as methane or methanol. It is proposed that TCE biodegradation by methanotrophs occurs by formation of TCE epoxide, which breaks down spontaneously in water to form dichloroacetic and glyoxylic acids and one-carbon products.

Journal Article↗
PubMed1981

Rates of microbial transformation of polycyclic aromatic hydrocarbons in water and sediments in the vicinity of a coal-coking wastewater discharge.

To facilitate predictions of the transport and fate of contaminants at future coal conversion facilities, rates of microbial transformation of polycyclic aromatic hydrocarbons were measured in stream water and sediment samples collected in the vicinity of a coal-coking treated wastewater discharge from November 1977 through August 1979. Six radiolabeled polycyclic aromatic hydrocarbons were incubated with sediment and water samples; CO(2), cell-bound C, and polar transformation products were isolated and quantified. Whereas CO(2) and bound C were major transformation products in sediment assays, soluble polar C dominated transformation in water samples. Mean rate constants (measured at 20 degrees C) in sediments collected downstream from the effluent outfall were 7.8 x 10 h (naphthalene), 1.6 x 10 h (anthracene), and 3.3 x 10 h [benz(a)anthracene], which corresponded to turnover times of 13, 62, and 300 h, respectively. No unequivocal evidence for transformation of benzo(a)pyrene or dibenz(a,h)anthracene was obtained. Only naphthalene and anthracene transformations were observed in water samples; rate constants were consistently 5- and 20-fold lower, respectively, than in the corresponding sediment samples. The measured rate constants for anthracene transformation in July 1978 sediment samples were not related to total heterotroph numbers. In late July 1978, the effluent was diverted from the primary study area; however, no differences were observed either in transformation rate constants or in the downstream/upstream sediment rate constant ratio. These results are consistent with the hypothesis that continuous inputs of polycyclic aromatic hydrocarbons result in an increased ability within a microbial community to utilize certain polycyclic aromatic hydrocarbons. However, because transformation rates remained elevated for more than 1 year after removal of the polycyclic aromatic hydrocarbon source, microbial communities may shift only slowly in response to changes in polycyclic aromatic hydrocarbon concentrations.

Journal Article↗
PubMed1978

Microbial transformation of polycyclic aromatic hydrocarbons in pristine and petroleum-contaminated sediments.

To determine rates of microbial transformation of polycyclic aromatic hydrocarbons (PAH) in freshwater sediments, C-labeled PAH were incubated with samples from both pristine and petroleum-contaminated streams. Evolved CO(2) was trapped in KOH, unaltered PAH and polar metabolic intermediate fractions were quantitated after sediment extraction and column chromatography, and bound cellular C was measured in sediment residues. Large fractions of C were incorporated into microbial cellular material; therefore, measurement of rates of CO(2) evolution alone would seriously underestimate transformation rates of [C]naphthalene and [C]anthracene. PAH compound turnover times in petroleum-contaminated sediment increased from 7.1 h for naphthalene to 400 h for anthracene, 10,000 h for benz(a)anthracene, and more than 30,000 h for benz(a)pyrene. Turnover times in uncontaminated stream sediment were 10 to 400 times greater than in contaminated samples, while absolute rates of PAH transformation (micrograms of PAH per gram of sediment per hour) were 3,000 to 125,000 times greater in contaminated sediment. The data indicate that four- and five-ring PAH compounds, several of which are carcinogenic, may persist even in sediments that have received chronic PAH inputs and that support microbial populations capable of transforming two- and three-ring PAH compounds.

Journal Article↗
PubMed1977

Rate of microbial transformation of polycyclic aromatic hydrocarbons: a chromatographic quantification procedure.

A chromatographic procedure has been developed for isolating and quantifying microbial transformation products of 14C-labeled polycyclic aromatic hydrocarbons. Transformation rates of naphthalene, anthracene, benz(a)anthracene, and benz(a)pyrene by a mixed bacterial population have been measured. With this procedure, extremely slow or incomplete transformations may be quantified that would not be detectable by previously used techniques.

Anthracenes↗