Uncovering enzymatic tools promoting lignocellulose breakdown in the anaerobic bacterium Ruminiclostridium cellulolyticum

Understanding the anaerobic deconstruction of recalcitrant lignocellulose remains challenging. Combining substrate composition and transcriptomic analyses, we shortlisted Ruminiclostridium cellulolyticum enzymes that modify lignocelullose and distinguished two members of the large SGNH hydrolase superfamily potentially enhancing lignocellulosic biomass degradation by acting on decorations of lignin and hemicelluloses but also on cross-links implicating lignin. Using genetic modifications, bioinformatics and biochemistry, we show they promote the plant cell wall ester-linked hydroxycinnamic acid derivatives release, a role never described for these proteins mainly synthesized by the restricted group of cellulolytic and cellulosome-producing bacteria. In addition to the recent observation of fungal limited lignin alterations in oxygen absence, this discovery is to the best of our knowledge, the first evidence of such anaerobic bacterial process that provides a better comprehension of the biogeochemical Earth's carbon cycle. Furthermore, a better knowledge of the anaerobic plant biomass degradation could help to design non-fossil resources based biotechnological applications, a cornerstone of bioeconomy development.