Prokaryotic community structure in algal photosynthetic biofilms from extreme acidic streams in Rio Tinto (Huelva, Spain)

Author Posting. © Spanish Society for Microbiology (SEM), 2008. This article is posted here by permission of Spanish Society for Microbiology (SEM) for personal use, not for redistribution. The definitive version was published in International Microbiology 11 (2008): 251-260, doi:10.2436/20.1501.01.69.Four algal photosynthetic biofilms were collected from the Rio Tinto (SW Spain) at four localities: AG, Euglena and Pinnularia biofilms; ANG, Chlorella and Pinnularia biofilms; RI, Cyanidium and Dunaliella biofilms; and CEM, Cyanidium, Euglena and Pinnularia biofilms. Community composition and structure were studied by a polyphasic approach consisting of 16S rRNA analysis, scanning electron microscopy by back-scattered electron detection mode (SEM-BSE), and fluorescence in-situ hybridization (FISH). Acidophilic prokaryotes associated with algal photosynthetic biofilms included sequences related to the Alpha-, Beta-, and Gammaproteobacteria (phylum Proteobacteria) and to the phyla Nitrospira, Actinobacteria, Acidobacteria and Firmicutes. Sequences from the Archaea domain were also identified. No more than seven distinct lineages were detected in any biofilm, except for those from RI, which contained fewer groups of Bacteria. Prokaryotic communities of the thinnest algal photosynthetic biofilms (<100 μm) were more related to those in the water column, including Leptospirillum populations. In general, thick biofilms (>200 μm) generate microniches that could facilitate the development of less-adapted microorganisms (coming from the surrounding environment) to extreme conditions, thus resulting in a more diverse prokaryotic biofilm.V.SE. and A.A are supported by a Ramón y Cajal contract from the Ministerio de Educación y Ciencia. EG-T. is supported by Instituto Nacional de Técnica Aeroespacial (INTA). This work was supported by a grant from the MECSpain (CGL2005-05470/BOS) and by Centro de Astrobiología (CSICINTA) and a grant from NASA Astrobiology Institute (NC-1054 LAZ)