Product toxicity and cometabolic competitive inhibition modeling of chloroform and trichloroethylene transformation by methanotrophic resting cells.

The rate and capacity for chloroform (CF) and trichloroethylene (TCE) transformation by a mixed methanotrophic culture of resting cells (no exogenous energy source) and formate-fed cells were measured. As reported previously for TCE, formate addition resulted in an increased CF transformation rate (0.35 day-1 for resting cells and 1.5 day-1 for formate-fed cells) and transformation capacity (0.0065 mg of CF per mg of cells for resting cells and 0.015 mg of CF per mg of cells for formate-fed cells), suggesting that depletion of energy stores affects transformation behavior. The observed finite transformation capacity, even with an exogenous energy source, suggests that toxicity was also a factor. CF transformation capacity was significantly lower than that for TCE, suggesting a greater toxicity from CF transformation. The toxicity of CF, TCE, and their transformation products to whole cells was evaluated by comparing the formate oxidation activity of acetylene-treated cells to that of non-acetylene-treated cells with and without prior exposure to CF or TCE. Acetylene arrests the activity of methane monooxygenase in CF and TCE oxidation without halting cell activity toward formate. Significantly diminished formate oxidation by cells exposed to either CR or TCE without acetylene compared with that with acetylene suggests that the solvents themselves were not toxic under the experimental conditions but their transformation products were. The concurrent transformation of CF and TCE by resting cells was measured, and results were compared with predictions from a competitive-inhibition cometabolic transformation model. The reasonable fit between model predictions and experimental observations was supportive of model assumptions.     

Effect of proteolytic digestion on the Ca2+-ATPase activity and subunits of latent and thiol-activated chloroplast coupling factor 1

The activation by proteases of the Ca2+-dependent ATPase of chloroplast coupling factor 1 (CF1) has been investigated. Using low concentrations of papain and trypsin, the increase in ATPase activity and the degradation of the five subunits of CF1 were compared. Sodium dodecyl sulfate-gel electrophoresis of protease-treated CF1 revealed that the delta subunit was very rapidly degraded and that the alpha and beta subunits were clipped. The gamma and epsilon subunits were more resistant to digestion. The modification of the alpha subunit of latent CF1 most closely correlated with the activation of Ca2+-ATPase activity. Trypsin treatment of dithiothreitol-activated CF1 resulted in a very rapid increase in Ca2+-ATPase activity and a corresponding rapid cleavage of the gamma subunit to a 25,000-dalton species. With more prolonged treatment, the 25,000-dalton species was cleaved to fragments of 14,000 and 11,000-daltons. Dithiothreitol treatment did not alter the rate of attack on the other subunits. The gamma subunit of heat-activated CF1 was also more susceptible to protease digestion. The increased protease sensitivity of the gamma subunit of soluble CF1 after treatment with dithiothreitol or heat mimics the increased protease sensitivity of the gamma subunit of bound CF1 when thylakoids are treated with trypsin during illumination (Moroney, J. V., and McCarty, R. E. (1982) J. Biol. Chem. 257, 5915-5920). These results suggest that the conformational changes that occur when purified CF1 is exposed to dithiothreitol are similar to those that CF1 bound to thylakoid membranes undergoes under illumination.     

Effects of exposure to sublethal levels of cadmium upon water-electrolyte status in the goldfish (Carassius auratus)

Goldfish were exposed to sublethal levels of cadmium (means of 44.5 and 380 μg Cd⁺⁺/l) for periods of 25 and 50 days, and their water-electrolyte status evaluated by reference to plasma and muscle levels of sodium, potassium and chloride and muscle water content. Significant changes in plasma chloride, tissue potassium and tissue water content were observed after 25 days in both test solutions. Specimens held at the more dilute cadmium concentration were apparently able to compensate for most of the initial cadmium effect and, after 50 days exposure, were characterized only by a continuing depression in plasma sodium level. This suggests that the cadmium MATC value for this species under the conditions employed is probably less than 45 μg Cd⁺⁺/l. Goldfish exposed to 380 μg Cd⁺⁺/l for 50 days exhibited significant deviations in plasma sodium and chloride levels as well as in tissue sodium and water content, and these parameters may provide useful indices of cadmium effects at sublethal concentrations.     

Environmental Risk Management Decision-Making in a Societal Context

Recent studies point to the need for improved understanding of environmental management frameworks designed to combine qualitative public and quantitative technical inputs in decision-making processes. Flux in public perception and concern about risks imply frameworks must be iterative in nature and incorporate a variety of assessment triggers in the form of decision points. A conceptual model is proposed here to explain the de facto operation of standard risk analytic frameworks within the broader sociopolitical milieu of public policy. The model is presented as a decision flow diagram that emphasizes setting environmental management goals based on societal input and the formulation of decision criteria for selecting management actions to achieve those goals. Prospective and retrospective decision control points operate to select management options that, respectively, avoid or reduce actual or predicted effects. Feedback loops that modify risk management outcomes are identified. Technical and scientific inputs (i.e., risk analysis) are assigned an essential information role within the framework and are responsible for informing the management process with the results of appropriately conducted and reviewed investigations. The proposed model is intended primarily to indicate how environmental risk management decision-making and associated technical assessments may be influenced by social pressures. It is hoped this understanding will lead to analytical transparency and better public communication of the environmental implications of policy options.     

A simple, quantitative approach to the coupling of photophosphorylation to electron flow in terms of proton fluxes.

A simple relationship between observed phosphorylation efficiencies (P/e ratios) and internal proton concentration in spinach chloroplast thylakoids has been derived. P/e ratios, varked by either changing the light intensity or by adding the energy transfer inhibitor, 4'-deoxyphlorizin, were found to change with internal proton concentration in accordance with this relationship. A quantitative prediction of the effect of uncouplers on the P/e ratio can probably also be made. By extrapolation of plots of observed P/e ratios against internal proton concentration divided by the overall rate of electron flow, a maximum intrinsic P/e of about 0.66 is obtained. Assuming that two protons appear inside thylakoids per electron transferred, a P/e ratio of 0.66 suggests that three internal protons are consumed for each ATP formed. Internal protons may be considered to be substrates for the phosphorylation reaction. Hill plots of phosphorylation rate vs. internal proton concentration also indicate that three protons are consumed for each ATP synthesized. Thus, the H+ concentration gradient behaves quantitatively, as well as qualitatively, as if it is the connecting link between electron flow and phosphorylation in illuminated thylakoids.     

Ant genomics sheds light on the molecular regulation of social organization

Ants are powerful model systems for the study of cooperation and sociality. In this review, we discuss how recent advances in ant genomics have contributed to our understanding of the evolution and organization of insect societies at the molecular level.     

Mechanistic Phenotypes: An Aggregative Phenotyping Strategy to Identify Disease Mechanisms Using GWAS Data

A single mutation can alter cellular and global homeostatic mechanisms and give rise to multiple clinical diseases. We hypothesized that these disease mechanisms could be identified using low minor allele frequency (MAF<0.1) non-synonymous SNPs (nsSNPs) associated with “mechanistic phenotypes”, comprised of collections of related diagnoses. We studied two mechanistic phenotypes: (1) thrombosis, evaluated in a population of 1,655 African Americans; and (2) four groupings of cancer diagnoses, evaluated in 3,009 white European Americans. We tested associations between nsSNPs represented on GWAS platforms and mechanistic phenotypes ascertained from electronic medical records (EMRs), and sought enrichment in functional ontologies across the top-ranked associations. We used a two-step analytic approach whereby nsSNPs were first sorted by the strength of their association with a phenotype. We tested associations using two reverse genetic models and standard additive and recessive models. In the second step, we employed a hypothesis-free ontological enrichment analysis using the sorted nsSNPs to identify functional mechanisms underlying the diagnoses comprising the mechanistic phenotypes. The thrombosis phenotype was solely associated with ontologies related to blood coagulation (Fisher''s p = 0.0001, FDR p = 0.03), driven by the F5, P2RY12 and F2RL2 genes. For the cancer phenotypes, the reverse genetics models were enriched in DNA repair functions (p = 2×10−5, FDR p = 0.03) (POLG/FANCI, SLX4/FANCP, XRCC1, BRCA1, FANCA, CHD1L) while the additive model showed enrichment related to chromatid segregation (p = 4×10−6, FDR p = 0.005) (KIF25, PINX1). We were able to replicate nsSNP associations for POLG/FANCI, BRCA1, FANCA and CHD1L in independent data sets. Mechanism-oriented phenotyping using collections of EMR-derived diagnoses can elucidate fundamental disease mechanisms.