Acetate scavenging and aromatic funneling of lignocellulose-derived carbon in the denitrifier Pseudomonas veronii

Lignocellulose degradation and denitrification frequently co-occur in soils and sediments with fluctuating or limited O ₂ availability, yet the ability of facultative denitrifiers to couple aromatic carbon turnover to nitrate respiration remains poorly understood. Here, we characterized a novel isolate, Pseudomonas veronii strain B19, for its genetic potential and physiological performance during growth on hemicellulose- and lignin-derived substrates under oxic and denitrifying conditions. Genome analysis revealed extensive aromatic catabolic pathways, including a complete β-ketoadipate route funneling lignin-derived compounds to central metabolism. Despite lacking classical endo-xylanases, the strain grew on acetylated xylan, with faster denitrification kinetics than on glucose. Proteomic and electron flow analyses indicate that xylan utilization proceeds via deacetylation and acetate assimilation through acetyl-CoA. Notably, the carbon source governed the denitrification regulatory phenotype: glucose elicited bet hedging and transient nitrite accumulation at the oxic–anoxic transition, whereas xylan-derived acetate supported a seamless transition to denitrification. On alkali-solubilized lignin, the strain utilized soluble monoaromatic compounds under both oxic and denitrifying conditions. Oxic metabolism proceeded through strong induction of O ₂ -dependent mono- and dioxygenases, enabling extensive aromatic catabolism, whereas under denitrifying conditions, conversion was only partial, with vanillate accumulation and electron-limited but stoichiometrically efficient nitrate reduction at minimal N ₂ O formation. Together, these findings demonstrate that B19 links lignocellulose-derived carbon turnover to denitrification under limited O ₂ , prioritizing electron flux over carbon yield. Its preference for soluble, low-molecular-weight lignin fractions and converging catabolic pathways indicate a role in downstream turnover of already-depolymerized lignin-derived aromatics, consistent with biological funneling and relevant to lignin valorization.