Assessing biochemical and biomolecular gradients along an ombrotrophic peat bog profile

Ombrotrophic peat bogs are not directly in contact with groundwater: since their genesis is related only to wet and dry deposition they are considered natural archives of extreme importance for the assessment of past ecological, environmental and climatic events. Etang de la Gruère is an ombrotrophic Swiss bog representing the longest continuous record of atmospheric deposition in continental Europe (corresponding to ca. 15,000 years of peat formation). Aim of the present study is to assess, in ca 20 samples along the peat bog profile, the presence and distribution of two very important classes of biomolecules: DNA and lipids. PCR-DGGE analysis of DNA targeting total bacteria and archaea allowed the identification of biodiversity patterns that clustered according to the profile depth and chemical analyses. It was found that the microbial communities changed significantly below ca 45 cm, where conditions are anoxic and molecules with higher molecular mass and degree of condensation are observed. Acidobacteria dominated the most superficial samples, while methanomicrobia were more common in the deepest samples. It was also found that the homologies scores decreased with depth, thus pointing to a less known microbial community composition in the oldest samples. Lipid analyses are now being carried out to integrate and extend the findings at DNA level. Specifically the analyses are focusing on phospholipid fatty acids (PLFAs) and tetraether lipids, which are respectively indicators of bacterial and archaeal microbial communities. In the case of tetraether lipids, their possible application as “paleo-thermometers” is also being tested.