A combination of hydrogeological, geochemical, and microbiological methods was used to document the biotransformation of trichloroethene (TCE) to ethene, a completely dechlorinated and environmentally benign compound, by naturally occurring microorganisms within a fractured dolomite aquifer. Analyses of groundwater samples showed that three microbially produced TCE breakdown products (cis-1,2-dichloroethene, vinyl chloride, and ethene) were present in the contaminant plume. Hydrogen (H2) concentra tions in groundwater indicated that iron reduction was the predominant terminal electron-accepting process in the most contaminated geologic zone of the site. Laboratory microcosms prepared with groundwater demonstrated complete sequential dechlorination of TCE to ethene. Microcosm assays also revealed that reductive dechlorination activity was present in waters from the center but not from the periphery of the contaminant plume. This dechlorination activity indicated that naturally occurring microorganisms have adapted to utilize chlorinated ethenes and suggested that dehalorespiring rather than cometabolic, microbial processes were the cause of the dechlorination. The addition of pulverized dolomite to microcosms enhanced the rate of reductive dechlorination, suggesting that hydrocarbons in the dolomite aquifer may serve as electron donors to drive microbially mediated reductive dechlorination reactions. Biodegradation of the chlorinated ethenes appears to contribute significantly to decontamination of the site.

Multiple signaling pathways are known to induce apoptosis in thymocytes through mechanisms that include the loss of mitochondrial membrane potential, cell shrinkage, caspase activation, and DNA degradation but little is known about the consequences of apoptosis on the properties of the plasma membrane. We have previously shown that apoptotic signals, including survival factor withdrawal and glucocorticoids, induce plasma membrane depolarization during rat thymocyte apoptosis, but the mechanisms involved in this process are unknown. We report here that inhibition of the Na(+)/K(+)-adenosine triphosphatase (Na(+)/K(+)-ATPase) with ouabain similarly depolarized control thymocytes and enhanced glucocorticoid-induced membrane depolarization, suggesting a link between Na(+)/K(+)-ATPase and plasma membrane depolarization of thymocytes. To determine whether repression of Na(+)/K(+)-ATPase levels within cells can account for the loss of plasma membrane potential, we assessed protein levels of the Na(+)/K(+)-ATPase in apoptotic thymocytes. Spontaneously dying thymocytes had decreased levels of both catalytic and regulatory subunits of Na(+)/K(+)-ATPase, and glucocorticoid treatment enhanced the loss of Na(+)/K(+)-ATPase protein. The pan caspase inhibitor (z-VAD) blocked both cellular depolarization and repression of Na(+)/K(+)-ATPase in both spontaneously dying and glucocorticoid-treated thymocytes; however, specific inhibitors of caspase 8, 9, and caspase 3 did not. Interestingly, glucocorticoid treatment simultaneously induced cell shrinkage and depolarization. Furthermore, depolarization and the loss of Na(+)/K(+)-ATPase protein were limited to the shrunken population of cells. The data indicate an important role for Na(+)/K(+)-ATPase in both spontaneous and glucocorticoid-induced apoptosis of rat thymocytes.

Abstract-Naphthalene has been transported approx. 400 m via groundwater flow from buried subsurface coal tar to an organic matter-rich seep area where the water emerges at the foot of a hill in a field study site. We have tested several hypotheses for explaining why naphthalene persists in seep sediments. In aerobic laboratory flask assays, conversion of 14 C-naphthalene to 14 CO 2 occurred and was not stimulated by amendments with vitamins or inorganic nutrients. Thus, neither toxicity nor nutrient limitation were the cause of naphthalene persistence. At the site, in situ sediment oxygen concentrations were below detection. Oxygenlimited naphthalene biodegradation was demonstrated both by measuring no conversion of 14 C-naphthalene to 14 CO 2 in samples of seep sediments prepared anaerobically and by measuring naphthalene loss from anaerobic nitrate-amended slurry-phase incubations of the sediment only after O 2 was added. However, when H 2 O 2 was added as an O 2 source to site sediments in situ in a randomized block design, no discernible naphthalene loss occurred. The possibility that decreased bioavailability might contribute to naphthalene persistence was investigated by monitoring 14 CO 2 evolved by microorganisms added to ␥-ray sterilized sediments that had been exposed under aseptic conditions to 14 C-labeled naphthalene for periods ranging from 0 to 28 d. Resulting patterns in the extent and rate of naphthalene mineralization revealed an inverse relationship to the duration of contact with the sediment, but only when the mixed microbial inoculum had been enriched on aqueous-phase naphthalene. We conclude that oxygen limitation is the most probable cause for lack of naphthalene biodegradation at our field study site. However, diffusion or sorption reactions may also play a role.

In primary rat thymocytes, both glucocorticoids and the withdrawal of in vivo survival factors elicit apoptosis. In this study we wanted to determine whether distinct pathways leading to apoptosis are engaged by these two stimuli. To address this question, we conducted a multiparametric analysis of cell viability, DNA fragmentation, activation of caspase-3-like activity, cell shrinkage, the loss of mitochondrial membrane potential, and externalization of phosphatidylserine in the absence and presence of protein and RNA synthesis. The role of caspase activity was also examined in both glucocorticoid-and survival factor withdrawal-induced cell death. We show that glucocorticoid-induced, but not spontaneous, loss of viability is dependent upon macromolecular synthesis and caspase activity. Furthermore, glucocorticoid-induced phosphatidylserine externalization and cell shrinkage are dependent upon gene regulation and caspase activity, whereas these features manifest independently of gene regulation and caspase activity in spontaneous death. In contrast, the loss of mitochondrial membrane potential was dependent upon macromolecular synthesis only in glucocorticoid-induced death and was independent of caspases in both spontaneous and dexamethasone-induced death. These results suggest that thymocytes can die by a caspase-independent mechanism and that a major difference between glucocorticoid- and survival factor deprivation-induced death is the dependence on gene expression.