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Molecular methods allow a comprehensive view on uncultured microbial communities in dimension stone. In the presented study, we focus on depth profiles of microbial colonization in sandstones with different porosity and overall durability. The sandstones were exposed to the environment for several years and were covered with a dense brown-greenish biofilm. Samples from the stone surface, from 0.5 cm and from 3.0 cm depths were taken under sterile conditions and subjected to analysis of microbial DNA (sequencing of 18S rRNA genes) and culturing experiments. A silica cemented Buntsandstein was just colonized at the stone surface, predominantly with algal and fungal microorganisms. Here, no environmental DNA could be isolated from depth profiles. From a calcitic Chirotheriensandstein with high pore size (shown by thin sections), environmental DNA from depths down to 3 cm could be retrieved. Apart from filamentous fungi and algae, mosses clearly dominated the microbial community. Hence, moss rhizoids or protonemata must be abundant as endoliths inside the stone material. It is reasonable to assume that the rhizoids may contribute to an increase in pore size by active penetration of the clastic material, even though colonization of the surface by mosses may not be necessarily obvious. This feature may imply stronger impact of stone decay induced by endolithic growth of bryophytes than hitherto observed. [ABSTRACT FROM PUBLISHER]

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]

For the first time the diversity of microscopic green algae (Chlorophyta) from calcified biofilms of karstic streams was analyzed using a combined approach based on pure cultures, i.e., 18S rRNA gene sequencing and microscopic analyses. Our study focused on two creeks in Germany. A considerable diversity of 34 species of green microalgae comprising three classes, the Trebouxiophyceae, Chlorophyceae and Ulvophyceae, was recovered. The biofilms of both streams were rather different in their species compositions which may reflect that they are exposed to differed hydrochemical conditions. The shallow Westerhöfer creek harbored predominantly Trebouxiophyceae and exhibited higher Mg2+ and SO42− concentrations. In contrast, the deeper, longer and spatially more heterogeneous Deinschwanger creek harbored numerous species of Chlorophyceae. A lower number of species from the Ulvophyceae were spread on both studied streams. The closest relatives of the identified species were from other freshwater habitats, but mostly from phytoplankton. However, also several species we recovered from freshwater for the first time; so far they have been known from terrestrial habitats only. Less than half of the recovered species could be identified with names at the species level based on high sequence identities with available sequences from named reference strains. Most recovered species could not be identified with names to species level, i.e., they may represent species for which no 18S rRNA gene sequence have become available yet or which have been retrieved for the first time. The genus Gongrosira Kützing, often reported from freshwater tufa-stromatolites, was found to represent most likely a collective morphotype formed by several genera nested within the Ulvophyceae. [ABSTRACT FROM AUTHOR]