To characterize a novel xanthine dehydrogenase (XDH) from Acinetobacter baumannii by recombinant expression in Escherichia coli and to assess its potential for industrial applications. The XDH gene cluster was cloned from A. baumannii CICC 10254, expressed heterologously in E. coli and purified to homogeneity. The purified recombinant XDH consisted of two subunits with the respective molecular weights of 87 kDa and 56 kDa according to SDS-PAGE. XDH catalysis was optimum at pH 8.5 and 40-45 A degrees C, was stable under alkaline conditions (pH 7-11) and the half-inactivation temperature was 60 A degrees C. The K (m), turnover number and catalytic efficiency for xanthine were 25 mu M, 69 s(-1) and 2.7 mu M-1 s(-1), respectively, which is an improvement over XDHs characterized previously. A. baumannii XDH is less than 50 % identical to previously identified XDH orthologs from other species, and is the first from the Acinetobacter genus to be characterized. The novel A. baumannii enzyme was found to be among the most active, thermostable and alkaline-tolerant XDH enzymes reported to date and has potential for use in industrial applications.