A multicopper oxidase is essential for manganese oxidation and laccase‐like activity in Pedomicrobium sp. ACM 3067

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Summary Pedomicrobium sp. ACM 3067 is a budding‐hyphal bacterium belonging to the α‐ Proteobacteria which is able to oxidize soluble Mn 2+ to insoluble manganese oxide. A cosmid, from a whole‐genome library, containing the putative genes responsible for manganese oxidation was identified and a primer‐walking approach yielded 4350 bp of novel sequence. Analysis of this sequence showed the presence of a predicted three‐gene operon, mox CBA. The mox A gene product showed homology to multicopper oxidases (MCOs) and contained the characteristic four copper‐binding motifs (A, B, C and D) common to MCOs. An insertion mutation of mox A showed that this gene was essential for both manganese oxidation and laccase‐like activity. The mox B gene product showed homology to a family of outer membrane proteins which are essential for Type I secretion in Gram‐negative bacteria. mox BA has not been observed in other manganese‐oxidizing bacteria but homologues were identified in the genomes of several bacteria including Sinorhizobium meliloti 1021 and Agrobacterium tumefaciens C58. These results suggest that mox BA and its homologues constitute a family of genes encoding an MCO and a predicted component of the Type I secretion system.