Enzymatic manganese(II) oxidation by a marine alpha-proteobacterium

A yellow-pigmented marine bacterium, designated strain SD-21, was isolated from surface sediments of San Diego Bay, San Diego, Calif., based on its ab ility to oxidize soluble Mn(II) to insoluble Mn(Ill, IV) oxides. 16S rRNA a nalysis revealed that this organism was most closely related to members of the genus Etythrobacter, aerobic anoxygenic phototrophic bacteria within th e alpha -4 subgroup of the Proteobacteria (alpha -4 Proteobacteria). SD-21, however, has a number of distinguishing phenotypic features relative to Er ythrobacter species, including the ability to oxidize Mn(II). During the lo garithmic phase of growth, this organism produces Mn(II)-oxidizing factors of approximate to 250 and 150 kDa that are heat labile and inhibited by bot h azide and o-phenanthroline, suggesting the involvement of a metalloenzyme . Although the expression of the Mn(II) oxidase was not dependent on the pr esence of Mn(II), higher overall growth yields were reached in cultures inc ubated with Mn(ll) in the culture medium. In addition, the rate of Mn(II) o xidation appeared to be slower in cultures grown in the light. This is the first report of Mn(II) oxidation within the alpha -4 Proteobacteria as well as the first Mn(Il)-oxidizing proteins identified in a marine gram-negativ e bacterium.