Assessing the Effect of Humic Substances and Fe(III) as Potential Electron Acceptors for Anaerobic Methane Oxidation in a Marine Anoxic System.

Sigrid Van Grinsven,Jaap S Sinninghe Damsté,Laura Villanueva

doi:10.3390/microorganisms8091288

Sigrid Van Grinsven, Jaap S Sinninghe Damsté + Show 1 more

Open Access

https://doi.org/10.3390/microorganisms8091288

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Abstract

Marine anaerobic methane oxidation (AOM) is generally assumed to be coupled to sulfate reduction, via a consortium of anaerobic methane-oxidizing archaea (ANME) and sulfate-reducing bacteria (SRB). ANME-1 are, however, often found as single cells, or only loosely aggregated with SRB, suggesting they perform a form of AOM independent of sulfate reduction. Oxidized metals and humic substances have been suggested as potential electron acceptors for ANME, but up to now, AOM linked to reduction of these compounds has only been shown for the ANME-2 and ANME-3 clades. Here, the effect of the electron acceptors anthraquinone-disulfonate (AQDS), a humic acids analog, and Fe3+ on anaerobic methane oxidation were assessed by incubation experiments with anoxic Black Sea water containing ANME-1b. Incubation experiments with 13C-methane and AQDS showed a stimulating effect of AQDS on methane oxidation. Fe3+ enhanced the ANME-1b abundance but did not substantially increase methane oxidation. Sodium molybdate, which was added as an inhibitor of sulfate reduction, surprisingly enhanced methane oxidation, possibly related to the dominant abundance of Sulfurospirillum in those incubations. The presented data suggest the potential involvement of ANME-1b in AQDS-enhanced anaerobic methane oxidation, possibly via electron shuttling to AQDS or via interaction with other members of the microbial community.

Highlights

Methane is a potent greenhouse gas (warming potential 34 times greater than CO2 (Forster et al 2007), and its atmospheric concentrations is rapidly increasing [1])
Diversity estimates based on 16S rRNA gene amplicon sequencing at 1000 m depth showed that the archaeal abundance was 2 × 105 copies per L (i.e., 1.5% of the total 16S rRNA reads; Figure 1). 21% of the archaeal 16S rRNA reads were classified as ANME-1b (0.3% of the total 16S rRNA reads; Table 1 and Table S2; Figure 2), corresponding to 4 × 104 copies per L
This question was addressed by performing incubation experiments with alternative electron acceptors, using suspended particulate matter collected from the anoxic Black Sea water column which is naturally relatively rich in sulfate (17 mM, Figure S1) and where ANME-1b is present in the deep waters

Summary

Introduction

Methane is a potent greenhouse gas (warming potential 34 times greater than CO2 (Forster et al 2007), and its atmospheric concentrations is rapidly increasing [1]). There is a large and continuous production of methane in anaerobic marine sediments by methanogenic archaea. Most of this methane is converted into carbon dioxide by oxidation, when methane is still in the sediment. The methane that is not oxidized in the sediments, gets released into the water column, via diffusion or bubbling. It can be emitted into the atmosphere. Methane oxidation in the water column can (partially) consume this methane and forms an additional filter to prevent methane emission from marine systems

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