Diversity of cultivated and metabolically active aerobic anoxygenic phototrophic bacteria along an oligotrophic gradient in the Mediterranean Sea 1Observatoire Océanologique de Roscoff, UMR7144, INSU-CNRS – Groupe Plancton Océanique, 29680 Roscoff, France
20 Jul 2011
2UPMC Univ Paris 06, UMR7144, Adaptation et Diversité en Milieu Marin, Station Biologique de Roscoff, 29680 Roscoff, France
3CNRS, UMR6023, Microorganismes: Génome et Environnement, Université Blaise Pascal, 63177 Aubière Cedex, France
Received: 21 Apr 2011 – Published in Biogeosciences Discuss.: 05 May 2011 Abstract. Aerobic anoxygenic phototrophic (AAP) bacteria play significant roles in the
bacterioplankton productivity and biogeochemical cycles of the surface
ocean. In this study, we applied both cultivation and mRNA-based molecular
methods to explore the diversity of AAP bacteria along an oligotrophic
gradient in the Mediterranean Sea in early summer 2008. Colony-forming units
obtained on three different agar media were screened for the production of
bacteriochlorophyll-a (BChl-a), the light-harvesting pigment of AAP bacteria.
BChl-a-containing colonies represented a low part of the cultivable fraction.
In total, 54 AAP strains were isolated and the phylogenetic analyses based
on their 16S rRNA and pufM genes showed that they were all affiliated to the
Alphaproteobacteria. The most frequently isolated strains belonged to
Citromicrobium bathyomarinum, and Erythrobacter and Roseovarius species. Most
other isolates were related to species not reported to produce BChl-a and/or
may represent novel taxa. Direct extraction of RNA from seawater samples
enabled the analysis of the expression of pufM, the gene coding for the M
subunit of the reaction centre complex of aerobic anoxygenic photosynthesis.
Clone libraries of pufM gene transcripts revealed that most phylotypes were
highly similar to sequences previously recovered from the Mediterranean Sea
and a large majority (~94 %) was affiliated to the
Gammaproteobacteria. The most abundantly detected phylotypes occurred in the western and
eastern Mediterranean basins. However, some were exclusively detected in the
eastern basin, reflecting the highest diversity of pufM transcripts observed in
this ultra-oligotrophic region. To our knowledge, this is the first study to
document extensively the diversity of AAP isolates and to unveil the active
AAP community in an oligotrophic marine environment. By pointing out the
discrepancies between culture-based and molecular methods, this study
highlights the existing gaps in the understanding of the AAP bacteria
ecology, especially in the Mediterranean Sea and likely globally.
Revised: 07 Jul 2011 – Accepted: 08 Jul 2011 – Published: 20 Jul 2011
Citation: Jeanthon, C., Boeuf, D., Dahan, O., Le Gall, F., Garczarek, L., Bendif, E. M., and Lehours, A.-C.: Diversity of cultivated and metabolically active aerobic anoxygenic phototrophic bacteria along an oligotrophic gradient in the Mediterranean Sea, Biogeosciences, 8, 1955-1970, doi:10.5194/bg-8-1955-2011, 2011.