Continuous enrichment cultures : insights into prokaryotic diversity and metabolic interactions in deep-sea vent chimneys

The prokaryotic diversity of culturable thermophilic communities of deep-sea hydrothermal chimneys was analysed using a continuous enrichment culture performed in a gas-lift bioreactor, and compared to classical batch enrichment cultures in vials. Cultures were conducted at 60 degrees C and pH 6.5 using a complex medium containing carbohydrates, peptides and sulphur, and inoculated with a sample of a hydrothermal black chimney collected at the Rainbow field, Mid-Atlantic Ridge, at 2,275 m depth. To assess the relevance of both culture methods, bacterial and archaeal diversity was studied using cloning and sequencing, DGGE, and whole-cell hybridisation of 16S rRNA genes. Sequences of heterotrophic microorganisms belonging to the genera Marinitoga, Thermosipho, Caminicella (Bacteria) and Thermococcus (Archaea) were obtained from both batch and continuous enrichment cultures while sequences of the autotrophic bacterial genera Deferribacter and Thermodesulftitator were only detected in the continuous bioreactor culture. It is presumed that over time constant metabolite exchanges will have occurred in the continuous enrichment culture enabling the development of a more diverse prokaryotic community. In particular, CO2 and H-2 produced by the heterotrophic population would support the growth of autotrophic populations. Therefore, continuous enrichment culture is a useful technique to grow over time environmentally representative microbial communities and obtain insights into prokaryotic species interactions that play a crucial role in deep hydrothermal environments

Absorption des phosphates Di- et Tricalcique chez l'homme

International audienc

Endolithic microbial communities in carbonate precipitates from serpentinite-hosted hyperalkaline springs of the Voltri Massif (Ligurian Alps, Northern Italy)

The Voltri Massif is an ophiolitic complex located in the Ligurian Alps close to the city of Genova (Northern Italy) where several springs discharge high pH (up to 11.7), low salinity waters produced by the active serpentinization of the ultramafic basement. Mixing of these hyperalkaline waters with the river waters along with the uptake of atmospheric carbon dioxide forms brownish carbonate precipitates covering the bedrock at the springs. Diverse archaeal and bacterial communities were detected in these carbonate precipitates using 454 pyrosequencing analyses of 16S ribosomal RNA (rRNA) genes. Archaeal communities were dominated by members of potential methane-producing and/or methane-oxidizing Methanobacteriales and Methanosarcinales (Euryarchaeota) together with ammonia-oxidizing Nitrososphaerales (Thaumarchaeota) similar to those found in other serpentinization-driven submarine and terrestrial ecosystems. Bacterial communities consisted of members of the Proteobacteria, Actinobacteria, Planctomycetes, Bacteroidetes, Chloroflexi, and Verrucomicrobia phyla, altogether accounting for 92.2 % of total retrieved bacterial 16S rRNA gene sequences. Amongst Bacteria, potential chemolithotrophy was mainly associated with Alpha- and Betaproteobacteria classes, including nitrogen-fixing, methane-oxidizing or hydrogen-oxidizing representatives of the genera Azospirillum, Methylosinus, and Hydrogenophaga/'Serpentinomonas', respectively. Besides, potential chemoorganotrophy was attributed mainly to representatives of Actinobacteria and Planctomycetales phyla. The reported 16S rRNA gene data strongly suggested that hydrogen, methane, and nitrogen-based chemolithotrophy can sustain growth of the microbial communities inhabiting the carbonate precipitates in the hyperalkaline springs of the Voltri Massif, similarly to what was previously observed in other serpentinite-hosted ecosystems

Fusibacter fontis sp. nov., a sulfur-reducing, anaerobic bacterium isolated from a mesothermic Tunisian spring

Strain KhalAKB1(T), a mesophilic, anaerobic, rod-shaped bacterium, was isolated from water collected from a mesothermic Tunisian spring. Cells were Gram-staining-Positive rods, occurring singly or in pairs and motile by one lateral flagellum. Strain KhalAKB1(T) grew at 15-45 degrees C (optimum 30 degrees C), at pH 5.5-8.5 (optimum pH 7.0) and in the presence of 0-35 g NaCl l(-1) (optimum 1 g NaCl l(-1)). It fermented yeast extract and a wide range of carbohydrates including cellobiose, D-glucose, D-ribose, sucrose, D-xylose, maltose, D-galactose and starch as electron donors. Acetate, ethanol, CO2 and H-2 were end products of glucose metabolism. It reduced elemental sulfur, but not sulfate, thiosulfate or sulfite, into sulfide. The DNA G+C content was 37.6 mol%. The predominant cellular fatty acids were C-14 : 0 and C-16 : 0. Phylogenetic analysis of the 16S rRNA gene sequence suggested Fusibacter bizertensis as the closest relative of this isolate (identity of 97.2 % to the type strain). Based on phenotypic, phylogenetic and genotypic taxonomic characteristics, strain KhalAKB1(T) is proposed to be assigned to a novel species within the genus Fusibacter, order Clostridiales, Fusibacter fontis sp. nov. The type strain is KhalAKB1(T) (=DSM 28450(T)=JCM 19912(T))

Halanaerobacter jeridensis sp. nov., isolated from a hypersaline lake

An obligatory anaerobic, moderately halophilic bacterium, designated strain CEJFG43(T), was isolated from a sample of sediment collected below the salt crust on the hypersaline El Jerid lake, in southern Tunisia. The cells of this novel strain were Gram-staining-negative, non-sporulating, motile, short rods. They grew in media with 6-30% (w/v) NaCl (optimum 15%), at 20-60 °C (optimum 45 °C) and at pH 5.5-9.5 (optimum pH 8.3). The micro-organism fermented glucose, fructose, ribose, raffinose, galactose, mannose, sucrose, maltose, xylose, mannitol, pyruvate and glycerol. The products of glucose fermentation were lactate, ethanol, acetate, H(2) and CO(2). The genomic G+C DNA content of strain CEJFG43(T) was 33.3 mol%. Phylogenetic analysis based on 16S rRNA gene sequences indicated that strain CEJFG43(T) belonged in the genus Halanaerobacter and was most closely related to Halanaerobacter lacunarum DSM 6640(T) (95.3% gene sequence similarity) and Halanaerobacter chitinivorans DSM 9569(T) (95.3%). The predominant cellular fatty acids were non-branched (C(16:0) and C(16:1)). Based on the phylogenetic and phenotypic evidence, strain CEJFG43(T) represents a novel species in the genus Halanaerobacter for which the name Halanaerobacter jeridensis sp. nov. is proposed. The type strain is CEJFG43(T) ( = DSM 23230(T) = JCM 16696(T))