The bacterial thiopurine methyltransferase tellurite resistance process is highly dependent upon aggregation properties and oxidative stress response.

Bacterial thiopurine methyltransferases (bTPMTs) can favour resistance towards toxic tellurite oxyanions through a pathway leading to the emission of a garlic-like smell. Gene expression profiling completed by genetic, physiological and electron microscopy analyses was performed to identify key bacterial activities contributing to this resistance process. Escherichia coli strain MG1655 expressing the bTPMT was used as a cell model in these experiments. This strain produced a garlic-like smell which was found to be due to dimethyl telluride, and cell aggregates in culture media supplemented with tellurite. Properties involved in aggregation were correlated with cell attachment to polystyrene, which increased with tellurite concentrations. Gene expression profiling supported a role of adhesins in the resistance process with 14% of the tellurite-regulated genes involved in cell envelope, flagella and fimbriae biogenesis. Other tellurite-regulated genes were, at 27%, involved in energy, carbohydrate and amino acid metabolism including the synthesis of antioxidant proteins, and at 12% in the synthesis of transcriptional regulators and signal transduction systems. Escherichia coli mutants impaired in tellurite-regulated genes showed ubiquinone and adhesins synthesis, oxidative stress response, and efflux to be essential in the bTPMT resistance process. High tellurite resistance required a synergistic expression of these functions and an efficient tellurium volatilization by the bTPMT.

Insertion sequence evolutionary patterns highlight convergent genetic inactivations and recent genomic island acquisitions among epidemic Burkholderia cenocepacia.

The Burkholderia cenocepacia B&B clone was found previously to be responsible for an epidemic outbreak within an intensive care unit in France. This clone belongs to the ST32 clonal complex, which is one of the most prevalent among French cystic fibrosis patients and is known to be related to the highly virulent ET12 clonal complex. Genomic repartition biases of insertion sequences (ISs) were investigated to improve our understanding of the evolutionary events leading to B. cenocepacia diversification and the emergence of such epidemic lineages. IS were used for tracking convergent genetic inactivations and recent DNA acquisitions. B. cenocepacia IS families and subgroups were compared in terms of genetic diversity and genomic architecture using fully sequenced genomes, PCR screening and DNA blot analysis. These analyses revealed several features shared by the B&B and ET12 epidemic clones. IS elements showed a frequent localization on genomic islands (GI) and indicated convergent evolution towards inactivation of certain loci. The IS407 subgroup of the IS3 family was identified as a good indicator of recently acquired GIs in clone ET12. Several IS407 elements showed strain-specific or clonal complex-specific localizations. IS407 DNA probing of a DNA library built from the B. cenocepacia B&B epidemic clone led to the identification of a recently acquired IS407-tagged GI likely to be conjugative and integrative. The B&B clone showed significant differences in its IS architecture from that of ST32 strains isolated from Czech cystic fibrosis patients.

Selection of nitrogen-fixing deficient Burkholderia vietnamiensis strains by cystic fibrosis patients: involvement of nif gene deletions and auxotrophic mutations.

Burkholderia vietnamiensis is the third most prevalent species of the Burkholderia cepacia complex (Bcc) found in cystic fibrosis (CF) patients. Its ability at fixing nitrogen makes it one of the main Bcc species showing strong filiations with environmental reservoirs. In this study, 83% (29 over 35) of the B. vietnamiensis CF isolates and 100% of the environmental ones (over 29) were found expressing the dinitrogenase complex (encoded by the nif cluster) which is essential in N(2) fixation. Among the deficient strains, two were found growing with ammonium chloride suggesting that they were defective in N(2) fixation, and four with amino acids supplements suggesting that they were harbouring auxotrophic mutations. To get insights about the genetic events that led to the emergence of the N(2)-fixing defective strains, a genetic analysis of B. vietnamiensis nitrogen-fixing property was undertaken. A 40-kb-long nif cluster and nif regulatory genes were identified within the B. vietnamiensis strain G4 genome sequence, and analysed. Transposon mutagenesis and nifH genetic marker exchanges showed the nif cluster and several other genes like gltB (encoding a subunit of the glutamate synthase) to play a key role in B. vietnamiensis ability at growing in nitrogen-free media. nif cluster DNA probings of restricted genomic DNA blots showed a full deletion of the nif cluster for one of the N(2)-fixing defective strain while the other one showed a genetic organization similar to the one of the G4 strain. For 17% of B. vietnamiensis clinical strains, CF lungs appeared to have favoured the selection of mutations or deletions leading to N(2)-fixing deficiencies.

Characterization of a novel selenium methyltransferase from freshwater bacteria showing strong similarities with the calicheamicin methyltransferase.

A novel group of Se-methyltransferases is presented. The genetic determinant, named mmtA, which revealed this group was isolated from selenite and selenate-resistant freshwater bacteria. E. coli expressing mmtA and grown with a Se supplement emitted dimethyl selenide (DMSe) and dimethyl diselenide (DMDSe). Phylogenetic analysis divided MmtA-like bacterial sequences into two clusters, one grouping MmtA with S- and O-methyltransferases, and one grouping UbiE C-methyltransferases. Se methylation by some of these MmtA phyletic neighbours was investigated.