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Formation of Filamentous Mn Oxide Particles by the Alphaproteobacterium Bosea sp. Strain BIWAKO-01

Mn-rich filamentous particles present in stratified water environments are considered bacteriogenic; however, little is known about their causative agents. This study investigated the production of these particles by an alphaproteobacterium, Bosea sp. strain BIWAKO-01. Particle formation was promoted in static cultures with slightly viscous medium at pH 6.0−6.3 under low-O2 conditions. The Mn(II) oxidation in cultures was slower in higher O2 concentration. These results suggested that pH and O2 concentration are important factors affecting filamentous Mn particle formation in the Mn(II) oxidizer. Lectin staining followed by fluorescence microscopy revealed the presence of specific carbohydrates in the filamentous structures. In addition, transmission electron microscopy, high angle annular dark field scanning transmission electron microscopy, and electron energy loss spectroscopy revealed the structural and spatial associations of Mn with O and C on a nanometer scale in filaments. The results suggested the occurrence of sheet-type Mn oxide likely due to the catalytic activity in exopolymeric substances including acidic polysaccharides.