Abstract
A wide variety of micro-organisms promote the oxidation or reduction of manganese, through indirect or direct mechanisms. An example of the latter category is Bacillus SGI, a marine organism isolated from a near-shore manganese sediment. Its mature dormant spores catalyze the oxidation of Mn 2+ to Mn 4+. The process requires molecular oxygen and is catalyzed by a spore coat component. The manganese oxide (Mn02) produced remains bound to the spore surface. The vegetative cells do not have the oxidizing capacity. They are able to reduce Mn4+ to Mn2+ under low-oxygen conditions. The reducing activity has a pH optimum of 7.5 and is abolished by preheating of the cells at 90° C for 5 minutes. Addition of mercuric chloride (HgCl2) (final concentration 0.01%) to cells which are actively reducing manganese oxide causes immediate cessation of the process. Manganese oxide reduction is also inhibited at high oxygen tensions and by inhibitors of the electron transport system. Bacillus cells contain b- and c-type cytochromes which are oxidized in situ when manganese oxide is added to an anoxic cell suspension. The results suggest that vegetative cells may use the manganese oxide formed by the spores from which they germinate as a terminal electron acceptor. The possible applications of manganese transforming micro-organisms in human society are discussed.
Published Version
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