Evolutionary Toxicology: Population-Level Effects of Chronic Contaminant Exposure on the Marsh Frogs (Rana ridibunda) of Azerbaijan

We used molecular methods and population genetic analyses to study the effects of chronic contaminant exposure in marsh frogs from Sumgayit, Azerbaijan. Marsh frogs inhabiting wetlands in Sumgayit are exposed to complex mixtures of chemical contaminants, including petroleum products, pesticides, heavy metals, and many other industrial chemicals. Previous results documented elevated estimates of genetic damage in marsh frogs from the two most heavily contaminated sites. Based on mitochondrial DNA (mtDNA) control region sequence data, the Sumgayit region has reduced levels of genetic diversity, likely due to environmental degradation. The Sumgayit region also acts as an ecological sink, with levels of gene flow into the region exceeding gene flow out of the region. Additionally, localized mtDNA heteroplasmy and diversity patterns suggest that one of the most severely contaminated sites in Sumgayit is acting as a source of new mutations resulting from an increased mutation rate. This study provides an integrated method for assessing the cumulative population impacts of chronic contaminant exposure by studying both population genetic and evolutionary effects

Nod2 Mediates Susceptibility to Yersinia pseudotuberculosis in Mice

Nucleotide oligomerisation domain 2 (NOD2) is a component of the innate immunity known to be involved in the homeostasis of Peyer patches (PPs) in mice. However, little is known about its role during gut infection in vivo. Yersinia pseudotuberculosis is an enteropathogen causing gastroenteritis, adenolymphitis and septicaemia which is able to invade its host through PPs. We investigated the role of Nod2 during Y. pseudotuberculosis infection. Death was delayed in Nod2 deleted and Crohn's disease associated Nod2 mutated mice orogastrically inoculated with Y. pseudotuberculosis. In PPs, the local immune response was characterized by a higher KC level and a more intense infiltration by neutrophils and macrophages. The apoptotic and bacterial cell counts were decreased. Finally, Nod2 deleted mice had a lower systemic bacterial dissemination and less damage of the haematopoeitic organs. This resistance phenotype was lost in case of intraperitoneal infection. We concluded that Nod2 contributes to the susceptibility to Y. pseudotuberculosis in mice

Biological Limitations of Dechlorination of cis-Dichloroethene during Transport in Porous Media

We applied a mathematical model to data from experimental column studies to understand the dynamics of successful and unsuccessful reductive dechlorination of chlorinated ethenes in groundwater under different flow conditions. In laboratory column experiments (reported previously), it was observed that complete dechlorination of cis-dichloroethene to ethene was sustained at high flow velocity (0.51 m/d), but that dechlorination failed at medium or low flow velocity (0.080 or 0.036 m/d). The mathematical model applied here accounts for transport of chlorinated ethenes in flowing groundwater, mass transfer of chlorinated ethenes between mobile groundwater and stationary biofilms, and diffusion and biodegradation within the biofilms. Monod kinetics with competitive inhibition are used to describe biodegradation. Nearly all parameters needed to solve the model are estimated independently from batch and nonreactive transport experiments. Comparing the model predictions to the experimental results permits the evaluation of three hypothesized biological limitations: insufficient supply of electron donor, decay of dechlorinators’ biomass, and reduction in bacterial metabolism rates. Any of these three limitations are able to adequately describe observed experimental data, but insufficient supply of electron donor is the most plausible explanation for failure of dechlorination. Therefore, an important conclusion of this investigation is that insufficient hydrogen production occurs if groundwater flow is too slow to provide adequate flux of electron donor. Model simulations were in good agreement with experimental results for both successful and unsuccessful dechlorination, suggesting the model is a valid tool for describing transport and reductive dechlorination. An implication of our findings is that in engineered or natural bioremediation of chloroethene-contaminated groundwater, not only must the proper dechlorinating organisms be present, but also proper groundwater flow conditions must be maintained or else dechlorination may fail