• Sciences du Vivant
  
• Sciences de l'environnement/Biodiversité et Ecologie
  

A novel, anaerobic, chemo-organotrophic bacterium, designated strain Ra1766H(T), was isolated from sediments of the Guaymas basin (Gulf of California, Mexico) taken from a depth of 2002  m. Cells were thin, motile, Gram-stain-positive, flexible rods forming terminal endospores. Strain Ra1766H(T) grew at temperatures of 25-45 °C (optimum 30 °C), pH 6.7-8.1 (optimum 7.5) and in a salinity of 5-60 g l(-1) NaCl (optimum 30 g l(-1)). It was an obligate heterotrophic bacterium fermenting carbohydrates (glucose and mannose) and organic acids (pyruvate and succinate). Casamino acids and amino acids (glutamate, aspartate and glycine) were also fermented. The main end products from glucose fermentation were acetate, butyrate, ethanol, H2 and CO2. Sulfate, sulfite, thiosulfate, elemental sulfur, fumarate, nitrate, nitrite and Fe(III) were not used as terminal electron acceptors. The predominant cellular fatty acids were C14  : 0, C16 : 1ω7, C16 : 1ω7 DMA and C16 : 0. The main polar lipids consisted of phosphatidylglycerol, diphosphatidylglycerol, phosphatidylethanolamine and phospholipids. The G+C content of the genomic DNA was 33.7 mol%. Phylogenetic analysis of the 16S rRNA gene sequence indicated that strain Ra1766H(T) was affiliated to cluster XI of the order Clostridiales, phylum Firmicutes. The closest phylogenetic relative of Ra1766H(T) was Geosporobacter subterraneus (94.2% 16S rRNA gene sequence similarity). On the basis of phylogenetic inference and phenotypic properties, strain Ra1766H(T) ( = DSM 27501(T) = JCM 19377(T)) is proposed to be the type strain of a novel species of a novel genus, named Crassaminicella profunda.

A novel obligately anaerobic, non-spore-forming, rod-shaped mesophilic, halophilic, Gram-stain-negative bacterium, was isolated from sediments of Guaymas Basin. The strain, designated Ra1766G1(T), grew at 20-40 °C (optimum, 30-35 °C) and at pH 6.0-8.0 (optimum, pH 6.5-7.5). It required 0.5-7.5 % NaCl (optimum, 2-3 %) for growth. Sulfate, thiosulfate, elemental sulfur, sulfite, fumarate, nitrate and nitrite were not used as terminal electron acceptors. Strain Ra1766G1(T) used cellobiose, glucose, mannose, maltose, arabinose, raffinose, galactose, ribose, sucrose, pyruvate and xylose as electron donors. The main fermentation product from glucose metabolism was acetate. The predominant cellular fatty acids were anteiso-C15 : 0, iso-C15 : 0, anteiso DMA-C15 : 0 and C16 : 0. The main polar lipids consisted of diphosphatidylglycerol, phosphatidylglycerol, iso-DMA-C15 : 0 glycolipids and phospholipids. The G+C content of the genomic DNA was 31.2 mol%. The closest phylogenetic relatives of strain Ra1766G1(T) were Natranaerovirga pectinivora AP3(T) (92.4 % 16S rRNA gene sequence similarity), Natranaerovirga hydrolytica APP2(T)(90.2 %) and Defluviitalea saccharophila 6LT2(T) (88.9 %). On the basis of phylogenetic inference and phenotypic properties, strain Ra1766G1(T) represents a novel species of a new genus for which the name Vallitalea guaymasensis is proposed. The type strain of the type species is Ra1766G1(T) ( = DSM 24848(T) = JCM17997(T)).

A 2.3-L bioreactor was specially adapted to grow hyperthermophilic microorganisms under controlled conditions of temperature, pH, redox potential and dissolved O(2). Using this bioreactor regulated at 80°C and pH 7.0, we demonstrated that Thermotoga maritima recovered its growth despite being exposed to oxygen for a short time (30 min with a maximum concentration of 23 μM of dissolved oxygen). Under these conditions, we demonstrated that O(2) uptake rate, estimated at 73.6 μmoles O(2) min(-1) g proteins(-1) for dissolved oxygen, was optimal and constant, when dissolved oxygen was present in a range of 22-5 μM. Transcription analyses revealed that during short oxygen exposure, T. maritima expressed genes coding for enzymes to deal with O(2) and reactive oxygen species (ROS) such as peroxides. Thus, genes encoding ROS-scavenging systems, alkyl hydroperoxide reductase (ahp), thioredoxin-dependent thiol peroxidase (bcp 2) and to a lesser extent neelaredoxin (nlr) and rubrerythrin (rbr), were found to be upregulated during oxygen exposure. The oxygen reductase FprA, homologous to the rubredoxin-oxygen oxidoreductase (ROO) found in Desulfovibrio species, is proposed as a primary consumer of O(2) in T. maritima. Moreover, the expression of frpA was shown to depend on the redox (Eh) level of the culture medium.