Differential modes of DNA binding by mismatch uracil DNA glycosylase from Escherichia coli: implications for abasic lesion processing and enzyme communication in the base excision repair pathway

Mismatch uracil DNA glycosylase (Mug) from Escherichia coli is an initiating enzyme in the base-excision repair pathway. As with other DNA glycosylases, the abasic product is potentially more harmful than the initial lesion. Since Mug is known to bind its product tightly, inhibiting enzyme turnover, understanding how Mug binds DNA is of significance when considering how Mug interacts with downstream enzymes in the base-excision repair pathway. We have demonstrated differential binding modes of Mug between its substrate and abasic DNA product using both band shift and fluorescence anisotropy assays. Mug binds its product cooperatively, and a stoichiometric analysis of DNA binding, catalytic activity and salt-dependence indicates that dimer formation is of functional significance in both catalytic activity and product binding. This is the first report of cooperativity in the uracil DNA glycosylase superfamily of enzymes, and forms the basis of product inhibition in Mug. It therefore provides a new perspective on abasic site protection and the findings are discussed in the context of downstream lesion processing and enzyme communication in the base excision repair pathway

Importance and controls of anaerobic ammonium oxidation influenced by riverbed geology

Rivers are an important global sink for excess bioavailable nitrogen: they convert approximately 40% of terrestrial N runoff per year (∼47 Tg) to biologically unavailable N 2 gas and return it to the atmosphere. At present, riverine N 2 production is conceptualized and modelled as denitrification. Anaerobic ammonium oxidation, known as anammox, is an alternative pathway of N 2 production important in marine environments, but its contribution to riverine N 2 production is not well understood. Here we use in situ and laboratory measurements of anammox activity using 15 N tracers and molecular analyses of microbial communities to evaluate anammox in clay-, sand-and chalk-dominated river beds in the Hampshire Avon catchment, UK during summer 2013. Abundance of the hzo gene, which encodes an enzyme central to anammox metabolism, varied across the contrasting geologies. Anammox rates were similar across geologies but contributed different proportions of N 2 production because of variation in denitrification rates. In spite of requiring anoxic conditions, anammox, most likely coupled to partial nitrification, contributed up to 58% of in situ N 2 production in oxic, permeable riverbeds. In contrast, denitrification dominated in low-permeability clay-bed rivers, where anammox contributes roughly 7% to the production of N 2 gas. We conclude that anammox can represent an important nitrogen loss pathway in permeable river sediments

Transnational Investments of the Tunisian Diaspora: Trajectories, Skills Accumulation and Constraints

This chapter is based on recent empirical data on Tunisians living in Switzerland. It focuses on their migration pathways and experiences, and it examines their propensity to engage in entrepreneurial and business activities in their home country. Despite the hopes generated by the revolution of 2011, there are many people in Tunisia, especially young males from disadvantaged regions, who have not enjoyed the positive changes in employment opportunities and professional prospects. This has led them to them emigrate to Europe to ensure an income for themselves and their families back in Tunisia. An online survey accompanied by follow-up interviews enabled us to observe the experiences of Tunisian diaspora entrepreneurs and their current and potential future transnational business and investment activities. This chapter shows how the internationalization and accumulation of networks and skills by Tunisians, resulting from the multiple destinations they traversed before arriving to Switzerland, has influenced their professional capacities and their business and entrepreneurial projects in Tunisia. Tunisians feel a strong motivation to contribute to the development process in their home country, and they tend to invest and open businesses in their villages of origin. Several enablers and obstacles that influence their actions are observed. A number of policy recommendations based on the experiences and aspirations of these Tunisians are included in the conclusions

New Rhizon in situ sampler for pore water studies in aquatic sediments: For example nutrient input from submarine groundwater discharge in costal areas.

To investigate coastal biogeochemical cycles, especially at the sediment/water interface,improved sampling methods are necessary. For this purpose, we developed apore water in situ sampler with miniature sampling devices, so called Rhizons. Rhizonsoil moisture samplers have been used as sampling devices in unsaturated soilsfor the last ten years. In aquatic science they have been rarely used to extract porewater from sediments. This study presents a new developed Rhizon In Situ Sampler(RISS) as a non-destructive and inexpensive tool for in situ pore water sampling. Fieldexperiments, tracer studies and numerical modeling were combined to assess the suitabilityof Rhizons for pore water sampling. Our investigations show that the RISS isa very suitable alternative to classical methods for in situ sampling. Combined withan in situ benthic chamber system the RISS allows studies of benthic fluxes and porewater profiles at the same location with negligible effect on the incubated sedimentwater interface. This allows improved calculation and modeling of transport and reactionprocesses. Results of nutrient and freshwater input into surface water derivedby in situ sampling of tidal flat sediments of the Wadden Sea (Sahlenburg/Cuxhaven,Germany) are presented. Long term deployments of the RISS and repetitive pore watersampling at the same location might support future studies of seasonal variation ofbenthic processes in sediments of the coastal zone and open ocean

Antimutator Role of DNA Glycosylase MutY in Pathogenic Neisseria Species

Genome alterations due to horizontal gene transfer and stress constantly generate strain on the gene pool of Neisseria meningitidis, the causative agent of meningococcal (MC) disease. The DNA glycosylase MutY of the base excision repair pathway is involved in the protection against oxidative stress. MC MutY expressed in Escherichia coli exhibited base excision activity towards DNA substrates containing A:7,8-dihydro-8-oxo-2′-deoxyguanosine and A:C mismatches. Expression in E. coli fully suppressed the elevated spontaneous mutation rate found in the E. coli mutY mutant. An assessment of MutY activity in lysates of neisserial wild-type and mutY mutant strains showed that both MC and gonococcal (GC) MutY is expressed and active in vivo. Strikingly, MC and GC mutY mutants exhibited 60- to 140-fold and 20-fold increases in mutation rates, respectively, compared to the wild-type strains. Moreover, the differences in transitions and transversions in rpoB conferring rifampin resistance observed with the wild type and mutants demonstrated that the neisserial MutY enzyme works in preventing GC→AT transversions. These findings are important in the context of models linking mutator phenotypes of disease isolates to microbial fitness