Detection of planktonic coenzyme factor 430 in a freshwater lake: small-scale analysis for probing archaeal methanogenesis

Atsushi Urai,Yoshinori Takano,Makoto Matsushita,Nanako O Ogawa,Naohiko Ohkouchi,Miyuki Ogawara,Hiroki Iwata,Masanori Kaneko,Ho-Dong Park,Hiroyuki Imachi

doi:10.1186/s40645-021-00450-7

Abstract

We present the first data describing molecular evidence of planktonic coenzyme factor 430 (hereafter referred to as F430), a key signature of methanogenic archaea, obtained from a water column sample in a freshwater lake in Japan. We report concentrations of native F430 ranging from 6.8–35 × 102 femto mol g-wet−1 and 8.5–86 × 102 femto mol g-wet−1 in the water column and core-top sediment, respectively. Among these profiles, the epimer F430 of the deactivated chemical formula was very low overall in both planktonic and benthic environments. Small subunit (SSU) rRNA gene sequencing revealed that the planktonic microbial community was clearly different from that of the benthic sediment. Planktonic cyanobacteria (e.g., Microcystis) were predominant in the water column, whereas a wide variety of bacteria and archaea, including methanogens (e.g., Methanobacterium, Methanoregula, Methanothrix, Methanosarcina, and Methanocella), were observed in the core-top sediment. These results suggest that the planktonic cyanobacterial community may be rapidly degraded at the water–sediment interface driven by activated benthic microbial heterotrophic processes.Graphic abstract

Highlights

Freshwater lakes are considered one of the main natural sources of methane (CH4) emissions in terrestrial environments, accounting for 6–16% of C H4 originating from natural sources (e.g., Bastviken et al 2004; Cole et al 2007; Holgerson and Raymond 2016; Günthel et al 2019)
The dissolved oxygen (DO) saturation ranged from 134 to 77%, suggesting that the water column was highly oxygenated from the surface to the bottom
The carbon and nitrogen isotope ratios presented in this study are in the typical cyanobacterial profiles and are consistent with the findings presented in previous reports (Yoshioka et al 1988; Ohkouchi and Takano 2014)

Summary

Introduction

Freshwater lakes are considered one of the main natural sources of methane (CH4) emissions in terrestrial environments, accounting for 6–16% of C H4 originating from natural sources (e.g., Bastviken et al 2004; Cole et al 2007; Holgerson and Raymond 2016; Günthel et al 2019). The major CH4 fraction released from freshwater lakes is produced by methanogenic archaea in anoxic sediments, and this is the terminal step of organic matter decomposition (e.g., Zepp Falz et al 1999; Chan et al 2005; Thauer et al 2008; Conrad 2009; Borrel et al 2011; Bukin et al 2018). It has been suggested that certain versatile methanogenic archaea thrive in anoxic microenvironments within planktonic cyanobacterial consortia (Batista et al 2019) and/or in the interior of floating fecal pellets (Wäge et al 2020), the entire CH4 production process in water column environments remains unclear

Methods

Results

Conclusion