Abstract

Large white mats of prokaryotic organisms (Archaea and Bacteria) have been recently discovered in the mangrove swamp of Guadeloupe (French West Indies). Here, we report evidence of two eukaryotic photosynthetic pigments in a giant multicellular Thaumarchaeota, Candidatus Photothauma chlorophyllense (Muller et al. 2010). Microfluorescence spectrometry in combination with thin layer chromatography points out the presence of chlorophyll a and pheophytin a after ethanol extraction. These two pigments were identical to those obtained from plants represented in this experiment by Leucaena leucocephala. In order to identify the structures were chlorophyll could be stocked into the Archaea, we also studied the filament structure by electronic microscopy. In ESEM, the analysis showed that each filament was composed by numerous archaeal cells covered by a thick membrane which can be removed by critical point treatment. In TEM sections, more electron dense structures were observed. They can be associated in the Archaea movement or be structures implicated in photosynthesis. For the first time, chlorophyll gene expression in Archeae is reported here, and could catalyze light-driven proton transfer across the cell membrane, although the gene has already been observed from clone bank of Pearl River, China. Thus, this discovery could reconsider the implication of Archaea in the establishment of photosynthesis and permit a better understanding of its evolution on earth. Furthermore, this study shows that mangrove shelters a wide diversity of microorganisms, thereby it is essential to study and protect its exceptional, but harvested, biodiversity proved here by the presence of Candidatus, Photothauma chlorophyllense.

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