Characterization of interaction between bacteria of petroleum reservoirs and water-hydrocarbons-rock interfaces

La récupération assistée des hydrocarbures par des microorganismes (MEOR) est une technologie potentiellement utilisable pour améliorer l’efficacité de l’extraction pétrolière. Cette technique utilise les capacités métaboliques de certaines souches bactériennes pour récupérer les huiles des réservoirs. Cependant, le manque de connaissances sur la physiologie et les activités métaboliques des microorganismes des réservoirs est un obstacle majeur pour le développement de cette approche. L’objectif de ce travail était d’étudier la physiologie des microorganismes indigènes de réservoirs pétroliers, en déterminant leurs capacités métaboliques, leurs conditions de croissances et leur positionnement taxonomique. Pour cela, trois activités physiologiques d’intérêt pour la MEOR : (1) la dégradation de l’hexadécane ;(2) la production de biosurfactant et (3) la formation de biofilm ont été évaluées sur 84 souches bactériens anaérobies isolées exclusivement de plusieurs réservoirs pétroliers. Ces isolats appartiennent à deux groupes métaboliques : les bactéries sulfato-réductrices (BSR) et les anaérobies fermentaires. Ainsi, cette prospection à donner une image de la diversité des souches de réservoirs possédant des activités appropriées pour la MEOR. Le séquençage et l’analyse phylogénétique du gène codant pour L’ARNr 16S a permet d’identifier deux nouvelles espèces bactériennes d’anaérobies fermentaires, SRL 4223 et SRL 4209 capables de produire des biosurfactants. Ainsi la caractérisation de ces deux isolats a révélé que la souche SRL 4223 présentait toutes les caractéristiques phénotypiques et génétiques autorisant sa classification un nouveau genre nommé Pleomorphochaeta caudata et que la souche SRL 4209 peut être affilié comme une nouvelle espèce de ce nouveau genre.The Microbial enhanced oil recovery (MEOR) is a potentially useful technology to improve the efficiency of oil extraction. This technique utilizes microorganisms and/or their metabolites (biosurfactants, polymers, biomass…etc.) to recover oil from reservoirs. However, the lack of basic knowledge about physiology and metabolic capacities of reservoir microorganisms is a major obstacle for the development of this approach. The objective of this work was to study the physiology of indigenous reservoir microorganisms by determining their metabolic capacities, their growth conditions and their taxonomic position. For this, three activities related to MEOR: (1) hexadecane degradation; (2) biofilm formation and (3) biosurfactant production were evaluated on 84 anaerobic bacterial strains isolated exclusively from several petroleum reservoirs. These isolates belong to two metabolic groups: sulfate-reducing bacteria (SRB) and anaerobic fermentative bacteria. This study gives a picture of the diversity of indigenous strains possessing proper activities for MEOR. Sequencing and phylogenetic analysis of 16S rRNA gene identified two new species of fermentative bacteria: SRL 4223 and SRL 4209, capable of producing biosurfactants. Characterization of these isolates revealed that the strain SRL 4223 had all the phenotypic and genetic characteristics allowing its classification as a new genus named Pleomorphochaeta caudata and the strain SRL 4209 was affiliated as a new species of this genus

Atypical stress response to temperature and NaOCl exposure leading to septation defect during cell division in Cupriavidus metallidurans CH34

International audienceCupriavidus metallidurans CH34 has long been known for its temperature-induced mutagenesis and mortality phenotype (TIMM), for which a genetic origin has been suggested repeatedly. In this report, we present microscopic-based evidences that the TIMM process actually starts with a septation defect, leading to aberrant cell morphologies. Moreover, the septation defect of CH34 could be induced by NaOCl, thus showing that the TIMM phenotype may be part of a more general stress response. Sequence analysis of a TIMM survivor exhibiting a recurrent recognizable lysA mutation ruled out the possibility of a genetic ground linking TIMM survival and peptidoglycan synthesis

Pleomorphochaeta caudata gen. nov., sp. nov., an anaerobic bacterium isolated from an offshore oil well, reclassification of Sphaerochaeta multiformis MO-SPC2T as Pleomorphochaeta multiformis MO-SPC2T comb. nov. as the type strain of this novel genus and emended description of the genus Sphaerochaeta

International audienceA strictly anaerobic Gram-stain-negative bacterium, designated strain SEBR 4223T, was isolated from the production water of an offshore Congolese oil field. Cells were non-motile, pleomorphic and had spherical, annular or budding shapes, often exhibiting long stalks. Strain SEBR 4223T grew on a range of carbohydrates, optimally at 37 °C and pH 7, in a medium containing 40 g l−1 NaCl. Predominant fatty acids were C14 : 0, C14 : 0 DMA, C16 : 0 and C16 : 1ω7c and the major polar lipids were phosphoglycolipids, phospholipids, glycolipids and diphosphatidylglycerol. The G+C content of the DNA was 28.7 mol%. Phylogenetic analysis, based on the 16S rRNA gene sequence, showed that strain SEBR 4223T and Sphaerochaeta multiformis MO-SPC2T formed a cluster with similarity to other species of the genus Sphaerochaeta of of less than 86 %. On the basis of the phenotypic characteristics and taxonomic analyses, we propose a novel genus, Pleomorphochaeta gen. nov., to accommodate the novel species Pleomorphochaeta caudata sp. nov., with SEBR 4223T (=DSM 103077T=JCM 31 475T) as the type strain. We also propose the reclassification of Sphaerochaeta multiformis MO SPC2T as Pleomorphochaeta multiformis MO-SPC2T comb. nov., the type strain of this novel genus and emend description of the genus Sphaerochaet

Zn2+ leakage and photo-induced reactive oxidative species do not explain the full toxicity of ZnO core Quantum Dots

International audienceMetal oxide nanoparticles (NPs), and among them metal oxides Quantum Dots (QDs), exhibit a multifactorial toxicity combining metal leaching, oxidative stress and possibly direct deleterious interactions, the relative contribution of each varying according to the NP composition and surface chemistry. Their wide use in public and industrial domains requires a good understanding and even a good control of their toxicity. To address this question, we engineered ZnO QDs with different surface chemistries, expecting that they would exhibit different photo-induced reactivities and possibly different levels of interaction with biological materials. No photo-induced toxicity could be detected on whole bacterial cell toxicity assays, indicating that ROS-dependent damages, albeit real, are hidden behind a stronger source of toxicity, which was comforted by the fact that the different ZnO QDs displayed the same level of cell toxicity. However, using in vitro DNA damage assays based on quantitative PCR, significant photo-induced reactivity could be measured precisely, showing that different NPs exhibiting similar inhibitory effects on whole bacteria could differ dramatically in terms of ROS-generated damages on biomolecules. We propose that direct interactions between NPs and bacterial cell surfaces prime over any kind of intracellular damages to explain the ZnO QDs toxicity on whole bacterial cells

Pleomorphochaeta naphthae sp. nov., a new anaerobic fermentative bacterium isolated from an oil field

International audienceA novel anaerobic fermentative bacterium, strain SEBR 4209T, was isolated from a water sample of a Congolese oil field. Strain SEBR 4209T is phylogenetically related to the genus Pleomorphochaeta , in the family Spirochaetaceae . Its closest relatives are Pleomorphochaeta caudata SEBR 4223T (94.5 % 16S rRNA gene sequence similarity) and Pleomorphochaeta multiformis MO-SPC2T (94.3 % similarity). Like the other members of this genus, cells have a pleomorphic morphology, in particular an annular shape and long stalks. Optimal growth was observed at 37 °C, at pH between 6.8 and 7.0, and with 40 g l−1 NaCl. This strain was only able to grow by fermentation of carbohydrates. The fermentation products from glucose utilization were acetate, ethanol, CO2 and H2. Predominant fatty acids were C14 : 0, C14 : 0 DMA, C16 : 0 and C16 : 1ω7c. The major polar lipids were phosphoglycolipids, phospholipids and glycolipids. The G+C content of the DNA was 29.6 mol%. Based on phenotypic characteristics and phylogenetic traits, strain SEBR 4209T is considered to represent a novel species of the genus Pleomorphochaeta , for which the name Pleomorphochaeta naphthae sp. nov. is proposed. The type strain is SEBR 4209T (=DSM 104684T=JCM 31871T)