The Complete Genome Sequence of Cupriavidus metallidurans Strain CH34, a Master Survivalist in Harsh and Anthropogenic Environments

Many bacteria in the environment have adapted to the presence of toxic heavy metals. Over the last 30 years, this heavy metal tolerance was the subject of extensive research. The bacterium Cupriavidus metallidurans strain CH34, originally isolated by us in 1976 from a metal processing factory, is considered a major model organism in this field because it withstands milli-molar range concentrations of over 20 different heavy metal ions. This tolerance is mostly achieved by rapid ion efflux but also by metal-complexation and -reduction. We present here the full genome sequence of strain CH34 and the manual annotation of all its genes. The genome of C. metallidurans CH34 is composed of two large circular chromosomes CHR1 and CHR2 of, respectively, 3,928,089 bp and 2,580,084 bp, and two megaplasmids pMOL28 and pMOL30 of, respectively, 171,459 bp and 233,720 bp in size. At least 25 loci for heavy-metal resistance (HMR) are distributed over the four replicons. Approximately 67% of the 6,717 coding sequences (CDSs) present in the CH34 genome could be assigned a putative function, and 9.1% (611 genes) appear to be unique to this strain. One out of five proteins is associated with either transport or transcription while the relay of environmental stimuli is governed by more than 600 signal transduction systems. The CH34 genome is most similar to the genomes of other Cupriavidus strains by correspondence between the respective CHR1 replicons but also displays similarity to the genomes of more distantly related species as a result of gene transfer and through the presence of large genomic islands. The presence of at least 57 IS elements and 19 transposons and the ability to take in and express foreign genes indicates a very dynamic and complex genome shaped by evolutionary forces. The genome data show that C. metallidurans CH34 is particularly well equipped to live in extreme conditions and anthropogenic environments that are rich in metals

An approach to freshwater cyanobacterial production and excretion : tentative application of a deterministic model

49 ref.International audienceThe rates of photosynthesis, respiration and carbon excretion by the cyanobacteriumOscillatoria rubescens D.C. were estimated at a range of light intensities between 0 and 60 μE m−2 s−1 (μmol photon m−2 s−1) using the14C method. A model of the evolution of cell carbon concentration based on the Hobsonet al. (1976) equations and taking excretion into account is presented. This model predicts that the sum of respiration and excretion rates increases more rapidly with light than the rate of photosynthesis and therefore maximum growth of theO. rubescens strain under study should be obtained at low light intensities, approximately 20 μE m−2 s−1 . Light rapidly increases the excretion rate and so induces a deficit in the carbon balance of the cell. In addition, the simultaneous increase in respiration rate, possibly due to photorespiration, contributes to carbon depletion at high irradiances. Thus, this model explains some of our observations, particularly the fact that growth is saturated at lower light intensities than photosynthesis.Nous avons estimé les taux de photosynthèse, de respiration et d'excrétion carboné chez Oscillatoria rubescens D.C. sous une gamme de conditions d'éclairement comprise entre 0 et 60 μE m−1 s−1 grâce à l'emploi de la méthode au14C. Un modèle d'évolution du carbone chez la cyanobactérie s'appuyant sur les équations de Hobsonet al. (1976) et prenant en compte la respiration et l'excrétion cellulaire est présenté. Ce modèle prévoit que la somme des taux de respiration et d'excrétion doit croître plus rapidement avec la lumière que le taux de photosynthèse. Il montre par ailleurs que la croissance maximale de la souche étudiée d'O. rubescens doit être trouvée à faible intensité lumineuse, environ 20 μE m−2 s−1. La lumière semble provoquer un accroissement rapide du taux d'excrétion et provoquer ainsi un deficit au niveau du bilan carboné de la cellule. De plus, l'accroissement simultané du taux de respiration probablement du à l'apparition de la photorespiration contribue à l'épuisement du carbone cellulaire aux fortes intensités lumineuses. Ainsi, ce modèle explique certaines de nos observations expérimentales et particulièrement le fait que la croissance est saturée à de plus faibles intensités lumineuses que la photosynthèse

The construction of a nopaline-inducible marker system for rapid detection of Agrobacterium strains

Tatiana Vallaeys, Nicholas C. McClure, Bruce Clare and Peter Murph

Faut-il craindre des effets secondaires du cuivre sur la biocoenose des sols viticoles ?

National audienc