Production of Metallogenium-like particles by heterotrophic manganese-oxidizing bacteria collected from a lake

Abstract

As a model of chemically stratified structure of environment typical to the chemocline of lakes, a semi- solid gradient medium was prepared to cultivate hetero- trophic manganese-oxidizing bacteria originally collected from a lake. The bacteria growing under the conditions described produced extracellularly MetalIogenium-like particles similar to those which are often detected in the chemocline of lakes. This suggested that the naturally occurring Metallogenium-like particles originated in ac- tivities of such heterotrophic manganese-oxidizing bac- teria. The manganese oxidation activity usually appeared only at the stationary phase of bacterial growth. The oxidation of Mn 2 + and the formation of Metallogenium- like particles by the bacteria were observed at neutral or slightly acidic pH, not under alkaline conditions, which is a conspicuous difference from the inorganic oxidation of Mn 2+ by O2. Bacterial manganese oxidation was stimulated by bicarbonate (50 or 500 gM). An experiment of addition of H202 to the incubation tubes isolated from atmosphere failed to confirm the availability of externally added H202 as the electron acceptor, suggesting that the bacterial manganese oxidation required the presence of O 2 .