Biotechnological Potential and Metabolic Diversity of Lignin-Degrading Bacteria from Decaying Tilia cordata Wood

Lignin is a complex aromatic polymer that constitutes a major fraction of plant biomass and represents a valuable renewable carbon resource. Naturally decaying wood serves as an environmental reservoir of microorganisms capable of degrading lignin. In this study, we isolated and characterized sixteen bacterial strains from decaying <i>Tilia cordata</i> wood using an enrichment culture technique with lignin as the sole carbon source. Taxonomic identification via 16S rRNA gene sequencing revealed microbial diversity spanning the genera <i>Bacillus</i>, <i>Pseudomonas</i>, <i>Stenotrophomonas</i>, and several members of the Enterobacteriaceae family, including <i>Raoultella terrigena</i> isolates. Metagenomic sequencing of the wood substrate revealed an exceptionally rich and balanced bacterial community (Shannon index H' = 5.07), dominated by <i>Streptomyces</i>, <i>Bradyrhizobium</i>, <i>Bacillus</i>, and <i>Pseudomonas</i>, likely reflecting a specialized consortium adapted to lignin rich late-stage decay. Functional phenotyping demonstrated that all isolates possess ligninolytic potential, evidenced by peroxidase/laccase-type activity through methylene blue decolorization. Dynamic Light Scattering (DLS) and HPLC analyses showed that some isolates, such as <i>Raoultella terrigena</i> MGMM806, effectively depolymerized lignosulfonate into low molecular weight fragments (1.23 nm), while others accumulated intermediate metabolites or completely mineralized the substrate. Growth profiling on monolignol substrates revealed a broad spectrum of catabolic specialization in lignin monomer degradation. The results demonstrate a complex system of metabolic partitioning within a natural bacterial consortium. This collection represents a foundational genetic resource for developing engineered biocatalysts and synthetic microbial communities aimed at the efficient conversion of lignin into valuable aromatic compounds.