Manganese oxidation and prokaryotic community analysis in a polycaprolactone-packed aerated biofilm reactor operated under seawater conditions

Masataka Aoki; Yukina Miyashita; Toru Miwa; Takahiro Watari; Takashi Yamaguchi; Kazuaki Syutsubo; Kazuyuki Hayashi

doi:10.1007/s13205-022-03250-y

Manganese oxidation and prokaryotic community analysis in a polycaprolactone-packed aerated biofilm reactor operated under seawater conditions

3 Biotech. 2022 Sep;12(9):187. doi: 10.1007/s13205-022-03250-y. Epub 2022 Jul 21.

Authors

Masataka Aoki^{1

2}, Yukina Miyashita², Toru Miwa³, Takahiro Watari⁴, Takashi Yamaguchi^{3

4}, Kazuaki Syutsubo^{1

5}, Kazuyuki Hayashi²

Affiliations

¹ Regional Environment Conservation Division, National Institute for Environmental Studies, 16-2 Onogawa, Tsukuba, Ibaraki 305-8506 Japan.
² Department of Civil Engineering, National Institute of Technology, Wakayama College, Gobo, Wakayama Japan.
³ Department of Science of Technology Innovation, Nagaoka University of Technology, Nagaoka, Niigata Japan.
⁴ Department of Civil and Environmental Engineering, Nagaoka University of Technology, Nagaoka, Niigata Japan.
⁵ Research Center for Water Environment Technology, School of Engineering, The University of Tokyo, Tokyo, Japan.

Abstract

Biogenic manganese oxides (BioMnOx) have been receiving increasing attention for the removal of environmental contaminants and recovery of minor metals from water environments. However, the enrichment of heterotrophic Mn(II)-oxidizing microorganisms for BioMnOx production in the presence of fast-growing coexisting heterotrophs is challenging. In our previous work, we revealed that polycaprolactone (PCL), a biodegradable aliphatic polyester, can serve as an effective solid organic substrate to enrich Mn-oxidizing microbial communities under seawater conditions. However, marine BioMnOx-producing bioreactor systems utilizing PCL have not yet been established. Therefore, a laboratory-scale continuous-flow PCL-packed aerated biofilm (PAB) reactor was operated for 238 days to evaluate its feasibility for BioMnOx production under seawater conditions. After the start-up of the reactor, the average dissolved Mn removal rates of 0.4-2.3 mg/L/day, likely caused by Mn(II) oxidation, were confirmed under different influent dissolved Mn concentrations (2.5-14.0 mg/L on average) and theoretical hydraulic retention time (0.19-0.77 day) conditions. The 16S rRNA gene amplicon sequencing analysis suggested the presence of putative Mn(II)-oxidizing and PCL-degrading bacterial lineages in the reactor. Two highly dominant operational units (OTUs) in the packed PCL-associated biofilm were assigned to the genera Marinobacter and Pseudohoeflea, whereas the genus Lewinella and unclassified Alphaproteobacteria OTUs were highly dominant in the MnOx-containing black/dark brown precipitate-associated biofilm formed in the reactor. Excitation-emission matrix fluorescence spectroscopy analysis revealed the production of tyrosine- and tryptophane-like components, which may serve as soluble heterotrophic organic substrates in the reactor. Our findings indicate that PAB reactors are potentially applicable to BioMnOx production under seawater conditions.

Keywords: 16S rRNA gene; Biodegradable polymer; Biogenic manganese oxide; Mn(II) oxidation.