Bioprospecting Microbial Diversity for Lignin Valorization: Dry and Wet Screening Methods.

Lignin is an abundant cell wall component, and it has been used mainly for generating steam and electricity. Nevertheless, lignin valorization, i.e. the conversion of lignin into high value-added fuels, chemicals, or materials, is crucial for the full implementation of cost-effective lignocellulosic biorefineries. From this perspective, rapid screening methods are crucial for time- and resource-efficient development of novel microbial strains and enzymes with applications in the lignin biorefinery. The present review gives an overview of recent developments and applications of a vast arsenal of activity and sequence-based methodologies for uncovering novel microbial strains with ligninolytic potential, novel enzymes for lignin depolymerization and for unraveling the main metabolic routes during growth on lignin. Finally, perspectives on the use of each of the presented methods and their respective advantages and disadvantages are discussed.

GH11 xylanase from Emericella nidulans with low sensitivity to inhibition by ethanol and lignocellulose-derived phenolic compounds.

An endo-ß-1,4-xylanase (X22) was purified from crude extract of Emericella nidulans when cultivated on submerged fermentation using sugarcane bagasse as the carbon source. The purified protein was identified by mass spectrometry and was most active at pH and temperature intervals of 5.0-6.5 and 50-60°C, respectively. The enzyme showed half-lives of 40, 10 and 7 min at 28, 50 and 55°C, respectively, and pH 5.0. Apparent Km and Vmax values on soluble oat spelt xylan were 3.39 mg/mL and 230.8 IU/mg, respectively, while Kcat and Kcat/Km were 84.6 s(-1) and 25.0 s(-1) mg(-1) mL. Incubation with phenolic compounds showed that tannic acid and cinnamic acid had an inhibitory effect on X22 but no time-dependent deactivation. On the other hand, ferulic acid, 4-hydroxybenzoic acid, vanillin and p-coumaric acid did not show any inhibitory effect on X22 activity, although they changed X22 apparent kinetic parameters. Ethanol remarkably increased enzyme thermostability and apparent Vmax and Kcat values, even though the affinity and catalytic efficiency for xylan were lowered.