The screening of manganese oxidizing bacteria and manganese oxidizing characteristics in soils under the abandoned field mining area
Jiang Qi¹, Lu Xingyan¹, Kenjin Fukuyama², Yasumichi Tsunashima², Maki Asano¹, Keiko Yamaji¹, Kenji Tamura¹
1 Institute of Life and Environmental Sciences, University of Tsukuba
2 Ningyo-toge Environmental Engineering Center, JAEA
Introduction
Manganese-oxidizing bacteria (MnOBs) are widely distributed in environments, including soil, freshwater, sludge sediments, and ocean, playing a significant role in the biogeochemical cycling of manganese. Manganese oxides are highly reactive minerals capable of adsorbing a substantial amount of heavy metal ions. They also possess the ability to oxidize variable-valence elements and organic compounds, thereby regulating the distribution of toxic substances and elements. These bio-manganese oxides play a crucial role in wastewater treatment, transformation of heavy metal pollutants, and the conversion of organic compounds. The objective of this study is to investigate new reservoirs of manganese-oxidizing bacteria and assess their potential in addressing soil pollution.
Materials and Methods
Seven manganese-oxidizing bacterial strains, exhibiting manganese oxidizing ability, were isolated and purified from the soil of the Ningyo-toge uranium deposit, named as N1, N2, N3, N4, N5, N6, and N7. The strains were classified through 16S rRNA gene sequence alignment and the construction of an evolutionary tree. Then the morphology and structure of manganese oxidation products produced by the seven strains of MnOBs were investigated using scanning electron microscopy-energy spectrometry (SEM-EDS) and X-ray crystal diffraction (XRD) analyses.
Results and Discussion
The key findings of this study are as follows:
(1) The seven strains were primarily isolated from the 0-20 cm surface soil layer. Based on the 16S rRNA results, all seven strains closely resembled Pseudomonas akapageensis in the database.
(2) Despite belonging to the genus Pseudomonas, the seven strains exhibited varying manganese oxidizing abilities. N1 demonstrated the most effective manganese oxidizing properties, whereas N5 exhibited the least efficient manganese oxidation.
(3) Following cultivation in the HAY medium, the seven strains of manganese-oxidizing bacteria produced diverse forms of manganese-containing sediments on the cell surface and between cells. XRD analysis identified disordered weak crystalline manganese oxides both within the cell and on the cell surface.
Part of this research was supported by the Japan Society for the Promotion of Science Grant-in-Aid for Scientific Research (A) (Project Number 19H01161) (Principal Investigator: Keiko Yamaji) and, the contract research by the Japan Atomic Energy Agency (Contract Number R03I057) (Principal researcher: Kenji Tamura).