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Composition and diversity of aeroterrestrial phototrophic microbial communities are up to now poorly understood. Here, we present a comparative study addressing the composition of algal communities on sandstone substrata based upon the analysis of rRNA gene clone libraries from environmental samples and crude cultures. From a west-facing, shaded wall area of the mediaeval castle ruin Gleichen (Thuringia, Germany), sequences mainly related to the green algae Prasiococcus and Trebouxia (Trebouxiophyceae) were retrieved. A south-west-facing, sun-exposed wall area was mainly colonized by Apatococcus and a Phyllosiphon-related alga. Just a few species, in particular Stichococcus-related strains, were ubiquitous in both areas. Samples from a basement vault exposed to low irradiance exhibited Chlorophyceae like Chromochloris and Bracteacoccus. Thus, most green algae on the daylight-exposed walls were affiliated to Trebouxiophyceae, whereas Chlorophyceae were dominant in samples taken from the site kept under low irradiance. Accordingly, cyanobacterial communities were different: the sun-exposed area was dominated by Synechococcus-related organisms, while on the shaded wall area, cyanobacteria were almost absent. The filamentous Leptolyngbya dominated samples from the basement vault. Scanning electron microscopy revealed endolithic algal morphotypes (coccoid algae and diatoms) dominant in open pores between mineral particles. Here, the organisms may be also involved in biogenic weathering of stone., (© 2012 Federation of European Microbiological Societies. Published by Blackwell Publishing Ltd. All rights reserved.)

Biofilms microscopically dominated by cyanobacteria and diatoms of two CO2 degassing karst-water creeks in Germany were investigated for their diversities along a gradient of calcification using SSU rRNA gene cloning and sequencing from environmental samples. The recovered totals of 731/413 cyanobacteria/diatom clones were grouped at 97/98% similarity levels into 28/29 molecular OTUs widely spread over their corresponding sequence phylogenies forming mostly monophyletic subclades. Sequence comparisons with named reference strains from NCBI/GenBank as well as newly determined references from the SAG culture collection left about half of the cyanobacteria OTUs still unidentified. Most of the diatom OTUs could be identified at least at the generic level. To improve identification also cultures of cyanobacteria and diatoms were established that allowed even species identification of some diatoms, but also revealed additional cyanobacteria hard to identify which were not recovered in the clone libraries. A significant correlation of the relative OTU abundances in clone libraries with values of SIcalcite was found and, therefore, redundancy analysis distinguished highly calcified sites far from the spring from those less calcified closer to the spring. The noncalcified spring sites were clearly distinct from all other sites by the presence of four cyanobacteria OTUs exclusively retrieved and that no diatoms could be recovered from there. Four cyanobacteria and three diatom OTUs were recovered whose increasing relative abundance per clone library was correlated with increasing calcification. This may indicate that not only cyanobacteria, but also diatoms are more directly involved in the biogenic impact on tufa formation than assumed previously. [ABSTRACT FROM AUTHOR]