Biological reductive dechlorination of tetrachloroethylene and trichloroethylene to ethylene under methanogenic conditions

A biological process for remediation of groundwater contaminated with tetrachloroethylene (PCE) and trichloroethylene (TCE) can only be applied if the transformation products are environmentally acceptable. Studies with enrichment cultures of PCE- and TCE-degrading microorganisms provide evidence that, under methanogenic conditions, mixed cultures are able to completely dechlorinate PCE and TCE to ethylene, a product which is environmentally acceptable. Radiotracer studies with [14C]PCE indicated that [14C]ethylene was the terminal product; significant conversion to 14CO2 or 14CH4 was not observed. The rate-limiting step in the pathway appeared to be conversion of vinyl chloride to ethylene. To sustain reductive dechlorination of PCE and TCE, it was necessary to supply an electron donor; methanol was the most effective, although hydrogen, formate, acetate, and glucose also served. Studies with the inhibitor 2-bromoethanesulfonate suggested that methanogens played a key role in the observed biotransformations of PCE and TCE.     

Reductive dechlorination of high concentrations of tetrachloroethene to ethene by an anaerobic enrichment culture in the absence of methanogenesis.

Tetrachloroethene, also known as perchloroethylene (PCE), is a common groundwater contaminant throughout the United States. The incomplete reductive dechlorination of PCE--resulting in accumulations of trichloroethene, dichloroethene isomers, and/or vinyl chloride--has been observed by many investigators in a wide variety of methanogenic environments. Previous mixed-culture studies have demonstrated that complete dechlorination to ethene is possible, although the final dechlorination step from vinyl chloride to ethene is rate limiting, with significant levels of vinyl chloride typically persisting. In this study, anaerobic methanol-PCE enrichment cultures which proved capable of dechlorinating high concentrations PCE to ethene were developed. Added concentrations of PCE as high as 550 microM (91-mg/liter nominal concentration; approximately 55-mg/liter actual aqueous concentration) were routinely dechlorinated to 80% ethene and 20% vinyl chloride within 2 days at 35 degrees C. The methanol level used was approximately twice that needed for complete dechlorination of PCE to ethene. The observed transformations occurred in the absence of methanogenesis, which was apparently inhibited by the high concentrations of PCE. When incubation was allowed to proceed for as long as 4 days, virtually complete conversion of PCE to ethene resulted, with less than 1% persisting as vinyl chloride. An electron balance demonstrated that methanol consumption was completely accounted for by dechlorination (31%) and acetate production (69%). The high volumetric rates of PCE dechlorination (up to 275 mumol/liter/day) and the relatively large fraction (ca. one-third) of the supplied electron donor used for dechlorination suggest that reductive dechlorination could be exploited for bioremediation of PCE-contaminated sites.     

A kinetic model for anaerobic digestion of biological sludge

The principal objective of this study was the development and evaluation of a comprehensive kinetic model capable of predicting digester performance when fed biological sludge, preliminary conversion mechanisms such as cell death, lysis, and hydrolysis responsible for rendering viable biological sludge organisms to available substrate were studied in depth. The results of this study indicate that hydrolysis of the dead, particulate biomass-primarily consisting of protein-is the slowest step, and therefore kinetically controls the overall process of anaerobic digestion of biological sludge. A kinetic model was developed which could accurately describe digester performance and predict effluent quality.     

Liver and intestinal fatty acid binding proteins in control and TGFβ1 gene targeted deficient mice

The effect of transforming growth factor beta-1 (TGF1) expression on fatty acid binding proteins was examined in control and two strains of gene targeted TGF1-deficient mice. Homozygous TGF1-deficient 129 × CF-1, expressing multifocal inflammatory syndrome, had 25% less liver fatty acid binding protein (L-FABP) when compared to control mice. The decrease in L-FABP expression was not due to multifocal inflammatory syndrome since homozygous TGF1-deficient/immunodeficient C3H mice on a SLID background had 36% lower liver L-FABP than controls. This effect was developmentally related and specific to liver, but not the proximal intestine, where L-FABP is also expressed. Finally, the proximal intestine also expresses intestinal-FABP (1-FABP) which decreased 3-fold in the TGF1-deficient/immunodeficient C3H mice only. Thus, TGF1 appears to regulate the expression of L-FABP and I-FABP in the liver and the proximal intestine, respectively.Abbreviations L-FABP liver fatty acid binding protein - I-FABP intestinal fatty acid binding protein - TGF1 transforming growth factor beta-1 - TNF- tumor necrosis factor- - MIP- macrophage inflammatory protein- - PMSF phenylmethyl sulfonyl fluoride - PBS phosphate buffered saline     

Phylogeny of Greya (Lepidoptera: Prodoxidae), based on nucleotide sequence variation in mitochondrial cytochrome oxidase I and II: congruence with morphological data

The phylogeny of Greya Busck (Lepidoptera: Prodoxidae) was inferred from nucleotide sequence variation across a 765-bp region in the cytochrome oxidase I and II genes of the mitochondrial genome. Most parsimonious relationships of 25 haplotypes from 16 Greya species and two outgroup genera (Tetragma and Prodoxus) showed substantial congruence with the species relationships indicated by morphological variation. Differences between mitochondrial and morphological trees were found primarily in the positions of two species, G. variabilis and G. pectinifera, and in the branching order of the three major species groups in the genus. Conflicts between the data sets were examined by comparing levels of homoplasy in characters supporting alternative hypotheses. The phylogeny of Greya species suggests that host-plant association at the family level and larval feeding mode are conservative characters. Transition/transversion ratios estimated by reconstruction of nucleotide substitutions on the phylogeny had a range of 2.0-9.3, when different subsets of the phylogeny were used. The decline of this ratio with the increase in maximum sequence divergence among taxa indicates that transitions are masked by transversions along deeper internodes or long branches of the phylogeny. Among transitions, substitutions of A-->G and T-->C outnumbered their reciprocal substitutions by 2-6 times, presumably because of the approximately 4:1 (77%) A+T-bias in nucleotide base composition. Of all transversions, 73%-80% were A<-->T substitutions, 85% of which occurred at third positions of codons; these estimates did not decrease with an increase in maximum sequence divergence of taxa included in the analysis. The high frequency of A<-->T substitutions is either a reflection or an explanation of the 92% A+T bias at third codon positions.