Identifying the European fossil fuel plumes in the atmosphere over the Northeast Atlantic Region through isotopic observations and numerical modelling.

As part of the Danish NEAREX project the origin and variability of anthropogenic atmospheric CO(2) over the Northeast Atlantic Region (NEAR) has been studied. The project consisted of a combination of experimental and modelling activities. Local volunteers operated CO(2) sampling stations, built at University of Copenhagen, for (14)C analysis at four locations (East Denmark, Shetland Isles, Faroe Isles and Iceland). The samples were only collected during winter periods of south-easterly winds in an attempt to trace air enriched in fossil-fuel derived CO(2) due to combustion of fossil fuels within European countries. In order to study the transport and concentration fields over the region in detail, a three-dimensional Eulerian hemispheric air pollution model has been extended to include the main anthropogenic sources for atmospheric CO(2). During the project period (1998-2001) only a few episodes of transport from Central Europe towards NEAR arose, which makes the data set for the evaluation of the method sparse. The analysed samples indicate that the signal for fossil CO(2), as expected, is largest (up to 3.7+/-0.4% fossil CO(2)) at the Danish location closest to the European emissions areas and much weaker (up to approximately 1.5+/-0.6% fossil CO(2)) at the most remote location. As the anthropogenic signal is weak in the clean atmosphere over NEAR these numbers will, however, be very sensitive to the assumed background (14)CO(2) activity and the precision of the measurements. The model simulations include the interplay between the driving processes from the emission into the boundary layer and the following horizontal/vertical mixing and atmospheric transport and are used to analyse the meteorological conditions leading to the observed events of high fossil CO(2) over NEAR. This information about the history of the air masses is essential if an observed signal is to be utilised for identifying and quantifying sources for fossil CO(2).

Analysis of an Escherichia coli mutant strain resistant to the cell-killing function encoded by the gef gene family.

The chromosomal genes gef and relF from Escherichia coli and the plasmid-encoded genes hok, flmA, srnB, and pndA constitute the gef gene family, which encodes a cell-killing function. In order to investigate the mechanism of cell killing we have isolated an E. coli mutant strain that is resistant to the overexpression of the toxic proteins encoded by the gef gene family. This phenotype requires at least two mutations, one of which has been mapped to 55.2 minutes. This mutation was sequenced and shown to represent a single base substitution in an open reading frame (ORF178) encoding a putative membrane protein having a molecular mass of 20.1 kDa. ORF178 and an upstream frame, ORF190, probably constitute an operon.

A family of genes encoding a cell-killing function may be conserved in all gram-negative bacteria.

The relF gene in Escherichia coli is related to the hok gene on plasmid R1. Both genes encode small proteins which, when overexpressed in E. coli lead to collapse of the membrane potential and cell death. A third gene, designated gef, which encodes a homologous cell-toxic protein, has been isolated from E. coli DNA. Both gef and relF are transcribed in E. coli and subject to post-transcriptional regulation which, in the case of gef, is coupled to translation of a leader sequence. The finding of homologous sequences in such distantly related bacteria as Agrobacterium and Rhizobium species suggests an important physiological role.