Bacterial 3-hydroxy fatty acids: Applicability as environmental markers in soils from the French Alps

Mr Pierre Véquaud1, Dr Sylvie Derenne1, Dr Sylvie Collin1, Mrs Christelle Anquetil1, Pr  Jérôme Poulenard2, Dr Pierre Sabatier2, Dr Arnaud Huguet1

1METIS, CNRS/Sorbonne Université/EPHE, Paris, France, 2EDYTEM, Université savoie Mont-Blanc/CNRS, Le Bourget-du-Lac, France

The composition of microbial membrane lipids has been shown to vary with environmental parameters in order to maintain an appropriate fluidity and permeability of the membrane. This is particularly the case for glycerol dialkyl tetraethers (GDGT), used for temperature and pH reconstructions in terrestrial settings, although other environmental parameters might also influence the GDGT distribution. Another family of lipids, 3-hydroxy fatty acids (3-OH FAs) was recently proposed as an alternative to GDGTs. To investigate the applicability of 3-OH FAs as temperature and pH proxies and understand the influence of environmental parameters on these lipids, 49 soils were collected between 200 and 3,000 m altitude in the French Alps. These soils cover a wide range of temperature (0°C to 15°C) and pH (3 to 8) and are representative of the diversity of soil vegetation and pedological covers along the mountain gradients. In agreement with previous studies, a significant correlation is observed between 3-OH FAs and pH. In contrast, no correlation could be shown with mean annual air temperature. Similarly, GDGTs are only poorly correlated with temperature in this sample set. This suggests that other parameters, such as vegetation, soil type or humidity are the main drivers of the variability of 3-OH FA and GDGT distribution. The influence of vegetation type and soil classification was tested on 3-OH FA relative abundances as the sampling allows differentiating 10 types of vegetation and 10 types of soil. Both parameters were shown to have a significant impact on the 3-OH FA distribution. This led us to build a model based on Artificial Neural Network, which allowed the reconstruction of soil types and vegetation with an accuracy of 89 %. This promising approach, developed on soils from the French Alps, will be further applied to a larger number of soil samples and also tested on GDGTs.


Distinguished senior scientist (DRCE) CNRS since 2016, Head of the biogeochemistry group of METIS laboratory. My research area is organic geochemistry and I combine various techniques of analytical chemistry to decipher the chemical structure of “geomaterials” to understand their formation pathway and behaviour in the environment. These “geomaterials” belong to a large diversity of natural environments such as sedimentary rocks, soil, natural waters and extraterrestrial materials. I co-authored 218 peer-reviewed papers and supervised 30 PhD students.

Awards: 2009 CNRS Silver Medal, 2019 Geochemical Society Alfred Treibs Medal

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