THESE Anne POSTEC Diversité de populations microbiennes ...

Résultats - Chapitre 3
Conclusion
Continuous enrichment culture performed in gas-lift bioreactor was shown to be an improved
method to expand our view of the cultivable microbial community inhabiting deep-sea
hydrothermal black smokers. The microbial diversity detected in traditional batch enrichment
cultures in vials was lower than that obtained from the bioreactor. All the sequences retrieved
in this study, archaeal or bacterial, obtained from cultures in vials or in the bioreactor, were
related to cultured microorganisms originating from deep-sea hydrothermal environments.
Molecular methods to assess the microbial diversity gave important data to guide the
isolation of new prokaryotic strains as shown in this study. Without change in the
experimental conditions, whole-cell hybridization analysis and data from the clone libraries
revealed a clear evolution of the community structure, indicating a dynamics among the
cultivated microbial community. Thanks to the continuous culture in bioreactor, it was
possible to maintain in culture heterotrophic strains and autotrophic strains for several
weeks. This was an unexpected result considering the organic rich medium supplied and
indicated that metabolic products of the heterotrophs helped to support the growth of the
autotrophic populations. The extended duration of culture in the bioreactor allowed cells to
interact primarily by means of end products of primary metabolism (fermentative pathway)
that are released and taken up. These interactions could be important factors permitting the
growth of as-yet uncultivated microorganisms.
The impact of the environment on a microbial community might be very intense in deep-sea
hydrothermal systems, since steep physico-chemical gradients are expected to exist, in the
range approximately of 350°C at pH3 to 4°C at pH7 in the case of a black smoker
investigated (Charlou, et al. 2002). The gas-lift bioreactor combined with the use of molecular
tools to monitor the microbial population structure could be used to investigate the effect of
environmental perturbations on the microbial community composition.
Acknowledgements
The authors want to thank P.M. Sarradin, chief scientist of the ATOS cruise, as well as the
captain and crew of the Atalante and the Victor team. This work was supported by Ifremer,
European VENTOX Program and Région Bretagne. We also wish to thank Dr C. L. Van
Dover for her helpful reading of the manuscript.
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