A cloned Bacillus halodurans multicopper oxidase exhibiting alkaline laccase activity

The gene product of open reading frame bh2082 from Bacillus halodurans C-125 was identified as a multicopper oxidase with potential laccase activity. A homologue of this gene, lbh1, was obtained from a B. halodurans isolate from our culture collection. The encoded gene product was expressed in Escherichia coli and showed laccase-like activity, oxidising 2,2'-azino-bis(3-ethylbenz-thiazoline-6-sulfonic acid), 2,6-dimethoxyphenol and syringaldazine (SGZ). The pH optimum of Lbh1 with SGZ is 7.5-8 (at 45 degrees C) and the laccase activity is stimulated rather than inhibited by chloride. These unusual properties make Lbh1 an interesting biocatalyst in applications for which classical laccases are unsuited, such as biobleaching of kraft pulp for paper production.