Paper-based electrodes as a tool for detecting ligninolytic enzymatic activities.

Lignin is the most important natural source of aromatic compounds. The valorisation of lignin into aromatics requires fractionation steps that can be catalysed by ligninolytic enzymes. However, one of the main limitations of biological lignin fractionation is the low efficiency of biocatalysts; it is therefore crucial to enhance or to identify new ligninolytic enzymes. Currently, the screening of ligninolytic activities on lignin polymers represents a technological bottenleck and hinders the characterization and the discovery of efficient ligninolytic biocatalysts. An efficient and fast method for the measurement of such enzymatic activities is therefore required. In this work, we present a new electrochemical tool based on lignin-coated paper electrodes for the detection and the characterization of ligninolytic activity. The suitability of this method is demonstrated using a catalase-peroxidase isolated from Thermobacillus xylanilyticus.

A thermostable bacterial catalase-peroxidase oxidizes phenolic compounds derived from lignins.

Lignocellulosic biomass is rich in lignins, which represent a bottomless natural source of aromatic compounds. Due to the high chemical complexity of these aromatic polymers, their biological fractionation remains challenging for biorefinery. The production of aromatics from the biological valorization of lignins requires the action of ligninolytic peroxidases and laccases produced by fungi and bacteria. Therefore, identification of efficient ligninolytic enzymes with high stability represents a promising route for lignins biorefining. Our strategy consists in exploiting the enzymatic potential of the thermophilic bacterium Thermobacillus xylanilyticus to produce robust and thermostable ligninolytic enzymes. In this context, a gene encoding a putative catalase-peroxidase was identified from the bacterial genome. The present work describes the production of the recombinant protein, its biochemical characterization, and ligninolytic potential. Our results show that the catalase-peroxidase from T. xylanilyticus is thermostable and exhibits catalase-peroxidase and manganese peroxidase activities. The electrochemical characterization using intermittent pulse amperometry showed the ability of the enzyme to oxidize small aromatic compounds derived from lignins. This promising methodology allows the fast screening of the catalase-peroxidase activity towards small phenolic molecules, suggesting its potential role in lignin transformation. KEY POINTS: • Production and characterization of a new thermostable bacterial catalase-peroxidase • The enzyme is able to oxidize many phenolic monomers derived from lignins • Intermittent pulse amperometry is promising to screen ligninolytic enzyme.