Stimulation of Mn2+ oxidation in Leptothrix discophora SS-1 by Cu2+ and sequence analysis of the region flanking the gene encoding putative multicopper oxidase MofA

The effect of Cu2+ on the Mn2+-oxidizing activity secreted by Leptothrix di scophora strain SS-1 was studied. Cu2+ stimulated the activity of spent med ium from stationary cultures when added during growth of the bacteria, alth ough cell yield decreased with increasing Cu2+ concentrations. The stimulat ion ic as tentatively explained by involvement of the putative multicopper oxidase MofA in Mn2+ oxidation. Cu2+ did not enhance the activity when adde d directly to spent medium, possibly because the ions had to be incorporate d during synthesis of the oxidizing factor Sequence analysis of the region downstream from the mofA gene resulted in identification of mofB, which enc odes a protein,vith a potential peptidyl-prolyl-cis-trans isomerase site, a nd mofC, which encodes a protein with a potential heme-binding site. The po ssibility that mofA, mofB, and mofC belong to one operon, and the possible functions of MofB and MofC, are discussed.