THESE Anne POSTEC Diversité de populations microbiennes ...

Résultats - Chapitre 3
thermophilic, anaerobic and strictly chemolithoautotrophic bacterium growing exclusively with
CO 2 as sole carbon source, H 2 as sole electron donor and sulfate as sole electron acceptor.
A second autotrophic strain identified from the continuous culture was affiliated to
Deferribacter abyssi (Miroshnichenko, et al. 2003b) and shared 99% similarity based on the
16S rDNA sequence. D. abyssi is a thermophilic, anaerobic and facultative
chemolithoautotrophic, isolated from an in situ growth chamber (Reysenbach, et al. 2000)
incubated for 2 days on Rainbow which used elemental sulfur or nitrate as electron
acceptors, similarly to the strain retrieved from the bioreactor.
Here in our experiment conducted under continuous culture, heterotrophs and
chemolithotrophs were co-cultivated in the continuous enrichment culture. The former most
probably used organic carbon provided by the continuous medium supply, whereas the latter
utilized hydrogen as electron donor and carbon dioxide as carbon source, both compounds
being end-products of the metabolism of fermentative microorganisms. This co-culture in
vitro represents a thermophilic fraction of the microbial diversity inhabiting the black smoker.
In the hydrothermal ecosystem, we may expect that chemolithoautotrophs should use the
geochemical energy associated with the mixed hydrothermal fluid, while heterotrophs might
utilize the organic carbon available at hydrothermal vent environments resulting from the high
productivity of micro- and macroorganisms (Giere et al., 2003).
Insight into microbial diversity at the Rainbow field
O’Brien et al. (1998) first published data on the microbiology at the Rainbow hydrothermal
site. From biomass collected by filtration, the authors determined by FISH analysis that the
proportion of Archaea was higher in the plume than in the surrounding seawater. In further
molecular studies, the microbial diversity of two black smokers of the Rainbow field, including
the chimney used in the present study, have been investigated through cloning and
sequencing of the 16S rRNA genes (Cambon-Bonavita, unpublished).
In addition to ‘Marinitoga hydrogenitolerans’, other new microorganisms were isolated very
recently from hydrothermal samples of the Rainbow site. A new archaeal species related to
the genus Thermococcus has been isolated and named ‘T. thioreducens’ (Pikuta et al. non
publié, 2004). To our knowledge, all the described new species originating from Rainbow are
thermophilic Bacteria. Vulcanithermus mediatlanticus (Miroshnichenko et al. 2003a) is a
facultative chemolithoheterotroph using oxygen or nitrate as electron acceptors and
molecular hydrogen as the energy source. Caminibacter profondus grows with H 2 as energy
source, sulfur, nitrate or oxygen as electron acceptors and CO 2 as carbon source
(Miroshnichenko et al. 2004). Caminibacter mediatlanticus is strictly anaerobic, and grows in
the presence of H 2 and CO 2 with nitrate or sulfur as electron acceptor (Voordeckers et al.
sous presse, 2005). Deferribacter abyssi, whose type strain JR T was isolated from the
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