Potential oxygen consumption and community composition of sediment bacteria in a seasonally hypoxic enclosed bay

Fumiaki Mori; Yu Umezawa; Ryuji Kondo; Gregory N Nishihara; Minoru Wada

doi:10.7717/peerj.11836

Potential oxygen consumption and community composition of sediment bacteria in a seasonally hypoxic enclosed bay

PeerJ. 2021 Aug 10:9:e11836. doi: 10.7717/peerj.11836. eCollection 2021.

Authors

Fumiaki Mori^{1

2

3}, Yu Umezawa⁴, Ryuji Kondo⁵, Gregory N Nishihara^{1

2}, Minoru Wada¹

Affiliations

¹ Graduate School of Fisheries and Environmental Sciences, Nagasaki University, Nagasaki, Nagasaki, Japan.
² Institute for East China Sea Research, Organization for Marine Science and Technology, Nagasaki University, Nagasaki, Nagasaki, Japan.
³ Kochi Institute for Core Sample Research, Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Kochi, Japan.
⁴ Department of Environmental Science on Biosphere, Tokyo University of Agriculture and Technology, Tokyo, Japan.
⁵ Department of Marine Science and Technology, Fukui Prefectural University, Fukui, Japan.

Abstract

The dynamics of potential oxygen consumption at the sediment surface in a seasonally hypoxic bay were monitored monthly by applying a tetrazolium dye (2-(4-iodophenyl)-3-(4-nitrophenyl)-5-phenyl-2H-tetrazolium chloride [INT]) reduction assay to intact sediment core samples for two consecutive years (2012-2013). Based on the empirically determined correlation between INT reduction (INT-formazan formation) and actual oxygen consumption of sediment samples, we inferred the relative contribution of biological and non-biological (chemical) processes to the potential whole oxygen consumption in the collected sediment samples. It was demonstrated that both potentials consistently increased and reached a maximum during summer hypoxia in each year. For samples collected in 2012, amplicon sequence variants (ASVs) of the bacterial 16S rRNA genes derived from the sediment surface revealed a sharp increase in the relative abundance of sulfate reducing bacteria toward hypoxia. In addition, a notable shift in other bacterial compositions was observed before and after the INT assay incubation. It was Arcobacter (Arcobacteraceae, Campylobacteria), a putative sulfur-oxidizing bacterial genus, that increased markedly during the assay period in the summer samples. These findings have implications not only for members of Delta- and Gammaproteobacteria that are consistently responsible for the consumption of dissolved oxygen (DO) year-round in the sediment, but also for those that might grow rapidly in response to episodic DO supply on the sediment surface during midst of seasonal hypoxia.

Keywords: Arcobacter; Bacterial community composition; Coastal hypoxia; Enclosed bay; Hypoxia; INT; Sediment oxygen consumption.

Grants and funding

This work was supported by JSPS KAKENHI (No. 22580202 and 17H03854) to Minoru Wada, and JSPS KAKENHI (No. 19K23685) and the Kurita Water and Environment Foundation (No. 18B075) to Fumiaki Mori. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.