Genome analysis of Achromobacter xylosoxidans RS1 reveals carbohydrate-active enzymes linked to lignin modification and dark fermentative hydrogen production from food waste

This study present Achromobacter xylosoxidans RS1 as a facultative bacterium capable of simultaneous lignin modification and direct hydrogen production from untreated food waste-a dual metabolic capability that offers new opportunities for consolidated bioprocessing by Achromobacter species. A. xylosoxidans RS1 achieved 55.2% lignin decolorization over seven days in mineral salt medium, with HPLC detection of the aromatic intermediate ferulic acid (2.2 mg/L) confirming active oxidative lignin catabolism. Plate assays revealed robust hydrolytic enzyme activities, including proteases (20.5 mm), amylases (17.5 mm), xylanases (16.8 mm), and cellulases (8.2 mm). Whole-genome sequencing produced a 6.58 Mbp draft genome encoding 50 carbohydrate-active enzymes (CAZymes), including one AA10 lytic polysaccharide monooxygenase, five AA3 oxidases, one AA7 oxidase, and seven CE1 esterases. These enzymes support enhanced cellulolytic, xylanolytic, and lignin-modifying activities. Batch dark fermentation experiments demonstrated that A. xylosoxidans RS1 produced hydrogen yields ranging from 0.506 to 0.946 mol H₂ mol⁻¹ substrate across xylose, glucose, carboxymethyl cellulose, starch, and untreated food waste. Xylose supported the highest hydrogen production potential (225 mL, 0.735 mol H₂ mol⁻¹ substrate) with rapid production kinetics, indicating efficient pentose utilization. In contrast, untreated food waste yielded the maximum molar hydrogen output (165 mL, 0.946 mol H₂ mol⁻¹ substrate), attributable to its heterogeneous carbohydrate composition that enhanced enzymatic accessibility and substrate solubilization. These findings indicate that A. xylosoxidans RS1 harbors a functional repertoire of oxidative CAZymes and hydrogen-metabolism pathway, enabling it to valorize food waste into hydrogen. The draft genome provides a valuable resource for further studies on facultative bacteria in waste-to-energy applications.