Unveiling the Genomic Potential of Citrobacter arsenatis RS3 for Sustainable Lignin Modification and Biohydrogen Production

This study characterizes Citrobacter arsenatis RS3 for its capacity to facilitate partial aromatic modification of lignin and produce biohydrogen under dark-fermentative conditions. The strain achieved a 55.2% reduction in UV280 absorbance and 39.1% Azure B reduction after 7 days aerobically with glucose. HPLC confirmed transient release of ferulic acid (2.512 mg L − 1) and vanillin (0.668 mg L − 1) at day 3, indicating oxidative cleavage of lignin side chains. Substantial extracellular hydrolytic activities were observed, with clearance zones of 28.5 mm (proteases), 15.3 mm (amylases), 7.8 mm (xylanases), and 6.7 mm (cellulases). Sequencing revealed a 6.01 Mbp genome encoding 5,453 CDSs, including CAZymes such as putative AA2 manganese peroxidases, AA1 multicopper oxidases, CE1 acetyl xylan esterases, and [NiFe]-hydrogenases, alongside pathways for aromatic compound metabolism. Under anaerobic conditions, RS3 produced biohydrogen yields ranging from 0.012 to 1.205 mol H2 mol −1 substrate, with xylose yielding the highest cumulative output of 360 mL H2 g −1 volatile solids. The strain’s enzymatic and metabolic characteristics indicate it may warrant further investigation for potential application in single-stage bioprocessing of lignocellulosic feedstocks; however, substantial research is needed to validate metabolic coupling and optimize processes before any conclusions can be drawn regarding its efficacy in reducing pretreatment demands at scale.