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°C and pH6.5 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 2,275m 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 Thermodesulfatator 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 H2 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 environment

Thermodesulfatator atlanticus sp. nov., a thermophilic, chemolithoautotrophic, sulfate-reducing bacterium isolated from a Mid-Atlantic Ridge hydrothermal vent.

International audienceA novel, strictly anaerobic, thermophilic, sulfate-reducing bacterium, designated strain AT1325(T), was isolated from a deep-sea hydrothermal vent at the Rainbow site on the Mid-Atlantic Ridge. This strain was subjected to a polyphasic taxonomic analysis. Cells were Gram-negative motile rods (approximately 2.4 x 0.6 microm) with a single polar flagellum. Strain AT1325(T) grew at 55-75 degrees C (optimum, 65-70 degrees C), at pH 5.5-8.0 (optimum, 6.5-7.5) and in the presence of 1.5-4.5 % (w/v) NaCl (optimum, 2.5 %). Cells grew chemolithoautotrophically with H2 as an energy source and SO4(2-) as an electron acceptor. Alternatively, the novel isolate was able to use methylamine, peptone or yeast extract as carbon sources. The dominant fatty acids (>5 % of the total) were C(16 : 0), C(18 : 1)omega7c, C(18 : 0) and C(19 : 0) cyclo omega8c. The G+C content of the genomic DNA of strain AT1325(T) was 45.6 mol%. Phylogenetic analyses based on 16S rRNA gene sequences placed strain AT1325(T) within the family Thermodesulfobacteriaceae, in the bacterial domain. Comparative 16S rRNA gene sequence analysis indicated that strain AT1325(T) belonged to the genus Thermodesulfatator, sharing 97.8 % similarity with the type strain of Thermodesulfatator indicus, the unique representative species of this genus. On the basis of the data presented, it is suggested that strain AT1325(T) represents a novel species of the genus Thermodesulfatator, for which the name Thermodesulfatator atlanticus sp. nov. is proposed. The type strain is AT1325(T) (=DSM 21156(T)=JCM 15391(T))

Metabolic challenges and key players in serpentinite-hosted microbial ecosystems

Serpentinite-hosted systems are amongst the most challenging environments for life on Earth. Serpentinization, a geochemical alteration of exposed ultramafic rock, produces hydrothermal fluids enriched in abiotically derived hydrogen (H2), methane (CH4), and small organic molecules. The hyperalkaline pH of these fluids poses a great challenge for metabolic energy and nutrient acquisition, curbing the cellular membrane potential and limiting electron acceptor, carbon, and phosphorous availability. Nevertheless, serpentinization supports the growth of diverse microbial communities whose metabolic make-up might shed light on the beginning of life on Earth and potentially elsewhere. Here, we outline current hypotheses on metabolic energy production, carbon fixation, and nutrient acquisition in serpentinizing environments. A taxonomic survey is performed for each important metabolic function, highlighting potential key players such as H2 and CH4 cycling Serpentinimonas, Hydrogenophaga, Methanobacteriales, Methanosarcinales, and novel candidate phyla. Methodological biases of the available data and future approaches are discussed

Optimisation of growth conditions for continuous culture of the hyperthermophilic archaeon Thermococcus hydrothermalis and development of sulphur-free defined and minimal media.

The hyperthermophilic archaeon Thermococcus hydrothermalis was cultivated in continuous culture in a gas-lift bioreactor in the absence of elemental sulphur on both proteinaceous and maltose-containing media. Optimal conditions (pH, temperature and gas flow rate), determined on complex media that yielded maximal growth rate and maximal steady state cell density, were obtained at 80 degrees C, pH 6 and gas sparging at 0.2 v v(-1) min(-1). Higher steady state cell densities were obtained on a medium containing maltose and yeast extract. In order to design a defined and minimal media, the nutritional requirements of T. hydrothermalis were then investigated using continuous culture in the absence of elemental sulphur in the gas-lift bioreactor. First, the complex nutriments were replaced and a defined medium containing maltose, 19 amino acids and the two nitrogenous bases adenine and thymine, was determined. Secondly, selective feedings and withdrawal of amino acids showed requirements for 14 amino acids

Defluviitaleaceae

International audienceDefining publication: Jabari et al. 2012, Etymology: De.flu.vi.i.ta.le.a.ce'a.e. N.L. n. Defluviitalea, type genus of the family; suff.aceae, ending to denote a family; N.L. fem. pl. n. Defluviitaleaceae, the Defluviitalea family

Fonticella

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Objection to the proposition of the new genus Abyssivirga

International audienceWe have read with interest the recent paper published by Schouw et al. [1] in IJSEM (Vol 66, pp. 1724–1734) entitled: 'Abyssivirga alkaniphila gen. nov., sp. nov., an alkane-degrading, anaerobic bacterium from a deep-sea hydrother-mal vent system, and emended descriptions of Natranaero-virga pectinivora and Natranaerovirga hydrolytica'. We disagree with the proposal of Abyssivirga as a new genus due to phylogenetic considerations as shown below. Indeed, we noticed that a BLAST analysis of the Abyssivirga alkani-phila 16S rRNA gene sequence indicated 99.4 % similarity with Vallitalea guaymasensis isolated from sediments of the Guaymas Basin, and 96.1 % with Vallitalea pronyensis isolated from a hydrothermal chimney in Prony Bay. Both Val-litalea species have been fully characterized in IJSEM [2, 3]. Based on phylogenetic analyses, we believe that the proposal of the new genus Abyssivirga should be reconsidered. A. alka-niphila should be reassigned to the genus Vallitalea, and possibly as a novel species, 'Vallitalea alkaniphila', if demonstrated by significant DNA–DNA hybridization and phenotypic differences. With the aim to clearly establish the phylogenetic position of A. alkaniphila and its effective affiliation to the genus Vallitalea, a phylogenetic tree is reconstructed here (Fig. 1)

Crassaminicella

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Serpentinicella

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