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. IMPORTANCE Denitrification and the breakdown of plant-derived carbon are central to nitrogen and carbon cycling in soils and sediments, yet how these processes intersect when oxygen is scarce is poorly understood. Most denitrifiers are thought to rely on simple carbon sources, while the breakdown of polymeric lignin is considered oxygen-dependent. Here, we show that the facultative anaerobe Pseudomonas veronii B19 couples the turnover of acetylated hemicellulose and soluble, low-molecular-weight lignin-derived aromatics to denitrification, sustaining respiration under oxygen limitation by prioritizing electron flux over carbon yield. Notably, the carbon source itself dictated the organism’s denitrification behavior, switching it between distinct regulatory strategies. By resolving these mechanisms in a single isolate, this work clarifies how facultative denitrifiers may process depolymerized plant carbon and shape nitrogen gas emissions in oxygen-limited environments, and identifies traits relevant to the downstream microbial valorization of lignin-derived aromatics.