Depth profiles of microbial colonization in sandstones

Abstract

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.

Keywords:

• 18S rRNA gene
• endolith
• environmental samples
• fungi
• green algae
• moss
• sandstone

Acknowledgement

Heidrun Stück (now Federal Institute for Geosciences and Natural Resources) kindly helped us in preparation of stone samples. We also thank Siegfried Siegesmund (Geoscience Center, University of Göttingen) for his support and helpful discussions. Parts of this study were performed in the laboratories of the experimental phycology and culture collection of algae at the University of Göttingen directed by Thomas Friedl. His support is gratefully acknowledged.

Funding

Funding by Deutsche Bundesstiftung Umwelt (DBU) and DFG FOR 571 (Geobiology of Organo- and Biofilms) is gratefully acknowledged.