Determining the effects of a spatially heterogeneous selection pressure on bacterial population structure at the sub-millimetre scale.

A key interest of microbial ecology is to understand the role of environmental heterogeneity in shaping bacterial diversity and fitness. However, quantifying relevant selection pressures and their effects is challenging due to the number of parameters that must be considered and the multiple scales over which they act. In the current study, a model system was employed to investigate the effects of a spatially heterogeneous mercuric ion (Hg(2+)) selection pressure on a population comprising Hg-sensitive and Hg-resistant pseudomonads.

Progress towards understanding the fate of plasmids in bacterial communities.

Plasmid-mediated horizontal gene transfer influences bacterial community structure and evolution. However, an understanding of the forces which dictate the fate of plasmids in bacterial populations remains elusive. This is in part due to the enormous diversity of plasmids, in terms of size, structure, transmission, evolutionary history and accessory phenotypes, coupled with the lack of a standard theoretical framework within which to investigate them.

Heterogeneous selection in a spatially structured environment affects fitness tradeoffs of plasmid carriage in pseudomonads.

Environmental conditions under which fitness tradeoffs of plasmid carriage are balanced to facilitate plasmid persistence remain elusive. Periodic selection for plasmid-encoded traits due to the spatial and temporal variation typical in most natural environments (such as soil particles, plant leaf and root surfaces, gut linings, and the skin) may play a role. However, quantification of selection pressures and their effects is difficult at a scale relevant to the bacterium in situ.

Sequence-based analysis of pQBR103; a representative of a unique, transfer-proficient mega plasmid resident in the microbial community of sugar beet.

The plasmid pQBR103 was found within Pseudomonas populations colonizing the leaf and root surfaces of sugar beet plants growing at Wytham, Oxfordshire, UK. At 425 kb it is the largest self-transmissible plasmid yet sequenced from the phytosphere. It is known to enhance the competitive fitness of its host, and parts of the plasmid are known to be actively transcribed in the plant environment.

Life in earth: the impact of GM plants on soil ecology?

The impact of changes incurred by agricultural biotechnology has led to concern regarding soil ecosystems and, rightly or wrongly, this has focused on the introduction of genetically modified (GM) crops. Soils are key resources, with essential roles in supporting ecosystems and maintaining environmental quality and productivity. The complexity of soils presents difficulties to their inclusion in the risk assessment process conducted for all GM plants.

The contribution of species richness and composition to bacterial services.

Bacterial communities provide important services. They break down pollutants, municipal waste and ingested food, and they are the primary means by which organic matter is recycled to plants and other autotrophs. However, the processes that determine the rate at which these services are supplied are only starting to be identified.

Transferable antibiotic resistance elements in Haemophilus influenzae share a common evolutionary origin with a diverse family of syntenic genomic islands.

Transferable antibiotic resistance in Haemophilus influenzae was first detected in the early 1970s. After this, resistance spread rapidly worldwide and was shown to be transferred by a large 40- to 60-kb conjugative element. Bioinformatics analysis of the complete sequence of a typical H.

Mesorhizobium septentrionale sp. nov. and Mesorhizobium temperatum sp. nov., isolated from Astragalus adsurgens growing in the northern regions of China.

Ninety-five rhizobial strains isolated from Astragalus adsurgens growing in the northern regions of China were classified into three main groups, candidate species I, II and III, based on a polyphasic approach. Comparative analysis of full-length 16S rRNA gene sequences of representative strains showed that candidate species I and II were Mesorhizobium, while candidate species III, which consisted of non-nodulating strains, was closely related to Agrobacterium tumefaciens. The phylogenetic relationships of the three candidate species and some related strains were also confirmed by the sequencing of glnA genes, which were used as an alternative chromosomal marker.

Identification and analysis of rhizobial plasmid origins of transfer.

Twelve Rhizobium leguminosarum isolates from France, Germany and the UK, each carrying between four and seven plasmids, were screened by PCR using primers designed to amplify partial traA and traC genes and the intergenic spacer (igs) between them, which is expected to contain oriT (the nick site for conjugal transfer). Five strains, 1062, RES-2, RES-6, RES-7 and RES-9, generated oriT-containing PCR fragments. Sequencing identified three types that are related to but different from other rhizobial plasmid oriT sequences in the database.

Two dnaB genes are associated with the origin of replication of pQBR55, an exogenously isolated plasmid from the rhizosphere of sugar beet.

Plasmid pQBR55 ( approximately 149 kb) represents one of five (Groups I-V) genetically distinct transfer proficient, mercury resistance plasmid groups that have been observed in the phytosphere pseudomonad community at a single geographic location in Oxford, UK. A 4.9-kb HindIII fragment was cloned from pQBR55 (a Group III plasmid) that facilitates autonomous replication of a narrow host range cloning vector, pKIL29, in the non-permissive host Pseudomonas putida UWC1.

Distribution of repC plasmid-replication sequences among plasmids and isolates of Rhizobium leguminosarum bv. viciae from field populations.

The distribution of four classes of related plasmid replication genes () within three field populations of in France, Germany and the UK was investigated using RFLP, PCR-RFLP and plasmid profile analysis. The results suggest that the four classes are compatible: when two or more different sequences are present in a strain they are usually associated with different plasmids. Furthermore, classical incompatibility studies in which a Tn5-labelled plasmid with a group IV sequence was transferred into field isolates by conjugation demonstrated that group IV sequences are incompatible with each other, but compatible with the other groups.

Enzymological and physiological consequences of restructuring the lipoyl domain content of the pyruvate dehydrogenase complex of Escherichia coli.

The core-forming lipoate acetyltransferase (E2p) subunits of the pyruvate dehydrogenase (PDH) complex of Escherichia coli contain three tandemly repeated lipoyl domains although one lipoyl domain is apparently sufficient for full catalytic activity in vitro. Plasmids containing IPTG-inducible aceEF-IpdA operons which express multilip-PDH complexes bearing one N-terminal lipoyl domain and up to seven unlipoylated (mutant) domains per E2p chain, were constructed. Each plasmid restored the nutritional lesion of a strain lacking the PDH complex and expressed a sedimentable PDH complex, although the catalytic activities declined significantly as the number of unlipoylated domains increased above four per E2p chain.