Assessing Lignin Types To Screen Novel Biomass-Degrading Microbial Strains: Synthetic Lignin as Useful Carbon Source

The isolation of lignin-degrading microbial strains may lead to the discovery of novel biocatalysts-peroxidases, laccases, and beta-etherases-potentially useful for lignin valorization. The inherent heterogeneity of lignin, together with the sometimes difficult accessibility to representative amounts of it, may become a hurdle for using lignin as a carbon source for screening purposes. This communication compares the screening of soil samples for lignin-degrading bacteria using as carbon sources either Organ Cat lignin or synthetically produced lignin. In both cases, the same microbial strains were isolated, suggesting that synthetic lignin-straightforwardly produced using peroxidases at laboratory scale-can be a valuable lignin substitute for microbial screenings and available in sufficient quantities. Likewise, OrganoCat lignin was dearomatized (50% and 100%) with a novel protocol using hydrogen peroxide and dimethylcarbonate, and the obtained derivatives were applied as carbon sources as well. In these cases, different microorganisms from those observed with real lignin derivatives were isolated from the same soil sample. Isolated microorganisms growing on nondegraded lignin polymers (Organ Cat and synthetic carbon sources) predominantly produced peroxidases, whereas strains growing on fully dearomatized lignins also secreted laccases.