Correlation between composition of microbial biofilms and weathering of exposed rock surfaces (biodeterioration) along a climatic and temporal gradient in Chile

This project's goals are to test for a correlation between the taxonomic composition of microbial biofilms covering open surfaces of igneous hard rocks and weathering/erosion of the rocks.

Funding:
DFG Fr 905/21-1, project 3 within the DFG SPP 1803 "EarthShape: Earth Surface Shaping by Biota";
from 1/2016 for three years

PIs:
Prof. Dr. Thomas Friedl
Prof. Dr. Joachim Reitner (Geobiology, Faculty of Geosciences and Geography, PI of parallel own project Re 665/40-1)

A precise assessment of the species (OTU) diversity of the biofilms targeting at their phototrophic and heterotrophic components will be performed. We will employ Next Generation Sequencing (NGS) methods to comprehensively assess changes in their microbial taxonomic composition along four different climatic zones in the Coastal Cordillera in Chile, i.e. the dedicated primary focus areas of the SPP 1803.

To establish a biological time scale biofilm successional changes and their ages at visually different stages of rock surface weathering will be determined using NGS combined with molecular phylogenetic analyses and 14C accelerator mass spectrometry. To increase insights into the functionality of the changes in biofilm diversity, high resolution imaging of rock hard part sections as well as biochemical analyses to trace signatures of microbial metabolic activity in relation to minerals will be performed at the biofilm-rock interface. Advanced microscopic methods will be used to examine the architectures of biofilm successional stages, spatial distribution and relative abundances of the organism groups within the biofilm as well as metabolic signatures.
For an even better assessing a biological time scale, also surface biofilms which already chipped of the rocks by weathering\erosion, i.e. detritus in the close vicinity of the rocks, will be examined for their biofilm composition. This will allow to assess whether and in as much the biofilm organisms may form seeds for colonization of the detritus and, at an even later stage, then for the colonization of soil. Therefore, these analyses will also provide an interface to the development of microbial communities in and on the soil.

In order to infer a geological time scale, the relationship between biofilm cover and rock erosion rate will be considered with Cosmogenic Nuclide Analyses (CNA). These analyses will help to reveal the effects of biofilm on erosion. Using CNA we will be able to test whether there is
1) a relationship between species (OTU) composition of the biofilms and rock erosion and
2) a gradual erosion of the surfaces (biodeterioration) is taking place.
By collecting CNA samples from areas with biofilm, mostly likely ubiquitous at the more humid two southern primary focus areas, and those where biofilm is absent (and unlikely to have existed previously) at arid sites in the most northern study area, the comparative concentrations of cosmogenic nuclides will be used to investigate whether biofilms exert a long-term control of surface deterioration.