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Open AccessArticle

Sequestration and Oxidation of Cr(III) by Fungal Mn Oxides with Mn(II) Oxidizing Activity

1
Department of Environmental Health Sciences, Graduate School of Nutritional and Environmental Sciences, University of Shizuoka, 52-1 Yada, Shizuoka 422-8526, Japan
2
Department of Environmental and Life Sciences, School of Food and Nutritional Sciences, University of Shizuoka, 52-1 Yada, Shizuoka 422-8526, Japan
3
Department of Biological Environment, Akita Prefectural University, Shimoshinjo-Nakano, Akita 010-0195, Japan
4
Advanced Science Research Center, Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195, Japan
*
Author to whom correspondence should be addressed.
Catalysts 2020, 10(1), 44; https://doi.org/10.3390/catal10010044
Received: 10 December 2019 / Revised: 26 December 2019 / Accepted: 26 December 2019 / Published: 31 December 2019
(This article belongs to the Special Issue State of the Art and Future Trends in Nanostructured Biocatalysis)
Biogenic manganese oxides (BMOs) have gained increasing attention for environmental application because of their sequestration and oxidizing abilities for various elements. Oxidation and sequestration of Cr(III) by BMOs, however, still remain unknown. We prepared BMOs in liquid cultures of Acremonium strictum strain KR21-2, and subsequently conducted single or repeated treatment experiments in Cr(NO3)3 at pH 6.0. Under aerobic conditions, newly formed BMOs exhibited a rapid production of Cr(VI) without a significant release of Mn(II), demonstrating that newly formed BMO mediates a catalytic oxidation of Cr(III) with a self-regeneration step of reduced Mn. In anaerobic solution, newly formed BMOs showed a cessation of Cr(III) oxidation in the early stage of the reaction, and subsequently had a much smaller Cr(VI) production with significant release of reduced Mn(II). Extraordinary sequestration of Cr(III) was observed during the repeated treatments under anaerobic conditions. Anaerobically sequestered Cr(III) was readily converted to Cr(VI) when the conditions became aerobic, which suggests that the surface passivation is responsible for the anaerobic cessation of Cr(III) oxidation. The results presented herein increase our understanding of the roles of BMO in Cr(III) oxidation and sequestration processes in potential application of BMOs towards the remediation of Cr(III)/Cr(VI) in contaminated sites. View Full-Text
Keywords: Cr(III) oxidation; Cr(III) sequestration; Cr(VI); biogenic manganese oxide; Mn(II)-oxidizing fungi Cr(III) oxidation; Cr(III) sequestration; Cr(VI); biogenic manganese oxide; Mn(II)-oxidizing fungi
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MDPI and ACS Style

Suzuki, R.; Tani, Y.; Naitou, H.; Miyata, N.; Tanaka, K. Sequestration and Oxidation of Cr(III) by Fungal Mn Oxides with Mn(II) Oxidizing Activity. Catalysts 2020, 10, 44.

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