Lignocellulose degradation: a proteomic and metagenomic study

Wood decay processes have recently attracted so much attention, as lignocellulose biomass (LCB) represents the most abundant renewable resource on the Earth and can provide fermentable sugar monomers convertible into value-added products. In order to improve the efficiency and ecological sustainability of the process, new insights about lignocellulosic biomass microbial degradation could be of fundamental importance. Organic matter rich environmental samples may host a large variety of microbes, most of them specialized in the degradation of LCB and thus important as potential sources of biochemical catalysts for value added products production, as well as for the global carbon cycle. The aim of this thesis is to study the LCB degradation by two different approaches, exploiting proteomic and metagenomic tools. Proteomic analyses were conducted on the secretomes of a bacterium, Cellulomonas fimi, grown in presence of carboxymethyl-cellulose or different pretreated LCBs as unique carbon sources. Zymography and enzyme activity assays confirmed the lignocellulose degrading capabilities of C. fimi, showing endoglucanase and xylanase activities. The comparison among secretomes (in terms of enzymatic activities and protein composition) obtained after growth on different substrates highlighted: i) the major proteins and CAZymes (Carbohydrate Active enZymes) secreted and involved in LCB degradation and ii) the substrate influence on the secretome protein composition and enzymatic activity. Metagenomic analyses were indeed conducted on two groups of representative samples (two decaying woods and two control soils) in order to characterize the microbial communities inhabiting them. The microorganisms (bacteria and fungi) found to be more represented in decaying wood samples than in soils could be considered the most probably responsible for wood degradation.