Hyperspectral Analysis and Enhanced Surface Probing of Representative Bacteria-mineral Interactions – HÆSPRI III

An important international scientific challenge for the next decade is to understand and clearly identify the response of biological and microbial systems interacting with their environment. To date, an increasing body of evidence suggests that a large amount of soil micro-organisms act directly or indirectly on several weathering processes affecting mineral integrity and element availability. Among these microorganisms, heterotrophic bacteria represent a key active compartment in natural ecosystems (soils and sediments) as well as man-managed systems (monuments, mine plants, contaminated wastes, agricultural soil...). In the past decades, the increase of environmental problems (sustained soil fertility, contaminant bioremediation, carbon sequestration...) and of economic challenges (metal extraction and recovery, waste management) has led to the development of a wide range of biotechnologies. Moreover, through feedback cycles that alter atmospheric carbon levels, microbially mediated weathering or deposition of minerals also have an impact on Earth's global climate. Thus, bacteria-mineral interactions have to be clearly delineated to model essential functions of soils and subsurface environments. Unravelling the underlying chemical reactions between bacteria (adhered or not) and the mineral and their rate-limiting steps could furthermore provide significant input for efficient solutions to environmental problems, particularly in soils. This project will allow a better understanding of silicate weathering fundamental mechanisms by soil bacteria and their variation as a function of available carbon sources, mineral surface reactivity and bacterial diversity. The proposed research should then contribute to changing the articulation of soil science and ecological research paradigms. To reach such a goal, the project is organized in 4 main work packages. The first work package aims at a proper definition of relevant bacteria/mineral associations through the selection of soil bacteria with specific weathering properties towards some soil minerals. The chosen minerals belong to the phyllosilicate family in which various parameters such as shape size and crystal chemistry can be easily adjusted. The aim of the second work package is to determine the bacterial metabolic pathways involved in mineral weathering. This will be achieved through various bio-assays coupled with an analysis of bacterial genes involved in weathering. In parallel, in order to obtain an in situ analysis of bacterial activity at mineral surfaces, bio-sensor-based approaches will be explored. These bio-sensors will be based on the specific fluorescence of genetically engineered bacteria. The third work package aims at the analysis of mineral surfaces modifications after bio-weathering. This will be achieved through the use of innovative spectroscopic techniques (two-photons florescence emission spectroscopy coupled with second harmonic generation, synchrtron-based imaging techniques) and more "classical" spectroscopic methods (Raman micro-spectrometry, high resolution gas adsorption). In that work package special attention will be devoted to signal processing procedures whose development will allow taking full advantage of the numerous spectroscopic data obtained. Finally, the fourth work package will deal with an advanced statistical and geo-statistical analysis of the data obtain in order to unravel multi-parametric interrelationships of the complex phenomena occurring at triple interfaces such as bacteria/mineral/aqueous solution interfaces. This program should then increase our knowledge of the nature and dynamics of the numerous processes involving various soil constituents. In the mid-term, this should allow a more realistic modelling of soil functionning.