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

Abstract

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.

Keywords:

• biogenic Mn oxides
• HAADF-STEM imaging and EELS mapping
• Lake Biwa
• Metallogenium
• Mn(II)-oxidizing Bosea

Acknowledgments

We appreciate Dr. Shiro Suzuki at Research Institute for Sustainable Humanosphere, Kyoto University for investigations of carbohydrates analysis including gas chromatography/mass spectrometry at Development and Assessment of Sustainable Humanosphere (DASH) system of the Research Institute for Sustainable Humanosphere.

Funding

This study was supported by the Sumitomo Foundation, Grant for Environment Research Project and JSPS KAKENHI Grant Number 26281042.