THESE Anne POSTEC Diversité de populations microbiennes ...

Résultats - Chapitre 3
the optimal growth temperature: not shown). No moderately thermophilic or thermophilic
Archaea were reported neither in this study; neither in the literature: except
Methanothermococcus okinawensis that grows optimally at 60-65°C (Takaï et al., 2002), all
the described archaeal species originating from deep-sea hydrothermal environments grow
optimally in pure culture at or above 75°C. This suggests that most Archaea thriving in deepsea
hydrothermal chimneys are hyperthermophilic.
Members of Thermococcales at deep-sea hydrothermal vents are widespread (Harmsen et
al. 1997, Nercessian et al. 2003, Reysenbach et al. 2000, Takai et al. 2001), and members of
the genus Thermococcus are some of the most numerous described hyperthermophiles from
deep-sea vents. They have been isolated from sulfidic chimneys (Godfroy et al. 1996),
sediments (Canganella et al. 1998), fluids (Grote, et al. 1999) and polychaete worms
(Pledger & Baross 1991). Investigation of their natural distribution showed that a viable
Thermococcus population was present in the surface layers of hydrothermal chimneys
(Harmsen, et al. 1997, Schrenk, et al. 2003, Takai, et al. 2001). Interestingly, members of
Thermococcales were not detected in molecular diversity analyses of hydrothermal deposits,
fluids or in situ colonizers deployed at low temperatures (Alain, et al. 2004, Huber et al. 2002,
Takai & Horikoshi 1999). However Thermococcus was detected in in situ colonizers
deployed in thermophilic conditions (Corre 2000, Nercessian, et al. 2003, Reysenbach, et al.
2000). These organisms should therefore be efficient surface colonizers. Furthermore,
Thermococcus populations were observed early in the enrichment cultures performed in vials
or bioreactor, at 60°C (this study) and 90°C (Postec, et al. 2005b). An early growth may
confer on Thermococcus microorganisms a great ecological advantage to colonize a new
hydrothermal environment. It may indicate that Thermococcus members are the primary
heterotroph colonizers. This is consistent with the observations and hypothesis emitted by
Nercessian et al. (2003), who showed that the proportion of Thermococcales-related
phylotypes was higher from the shortest deployments (4-7 days) of in situ collectors than in
longer deployments. Theses results differ from observations and hypothesis as reported by
Reysenbach et al. (2000) suggesting that chemolithoautotrophs would be the first colonizers
of vent surfaces and that thermophilic heterotrophs such Thermococcales would emerge
after a sufficient organic carbon accumulation.
Bacterial diversity
All the sequences retrieved in our enrichment cultures were related to cultivated
microorganisms originating from deep-sea hydrothermal vents. Members of the genera
Caminicella and Marinitoga were detected in the enrichment cultures performed in vials and
in the bioreactor, whatever the incubation time or the occurrence of subculturing, suggesting
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