This proposal focuses on the development of new techniques and strategies for the directed evolution of enzymes useful for industrial (white) biotechnology, including the development of new genetic methodologies to improve the potential of variant libraries, as well as new screening tools to broaden the range of targets for directed evolution. Specifically, the proposed project will apply these new methodologies to plant cell-wall degrading enzymes, namely cellulases and hemicellulases, which are crucial biocatalysts for the production of second-generation lignocellulose-derived biofuels. The enzymes targeted in this proposal are phylogenetically-related, share the same fold, catalyze the same chemical transformation on a large number of structurally related substrates and thus provide good starting points to switch substrate specificities by directed evolution. In order to achieve these challenging objectives, the proposed project will combine new technical advances: on the one hand methodologies to construct gene libraries and stability compensation strategies, and on the other hand new screening approaches of unprecedented throughput based on compartmentalized screening in microdroplets that are processed in microfluidic devices.