Aerobic methane oxidation under copper scarcity in a stratified lake

Carole Guggenheim,Helmut Bürgmann,Bernhard Wehrli,Andreas Brand,Laura Sigg

doi:10.1038/s41598-019-40642-2

Carole Guggenheim, Helmut Bürgmann + Show 3 more

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https://doi.org/10.1038/s41598-019-40642-2

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Abstract

Aerobic methane-oxidizing bacteria (MOB) substantially reduce methane fluxes from freshwater sediments to the atmosphere. Their metalloenzyme methane monooxygenase (MMO) catalyses the first oxidation step converting methane to methanol. Its most prevalent form is the copper-dependent particulate pMMO, however, some MOB are also able to express the iron-containing, soluble sMMO under conditions of copper scarcity. So far, the link between copper availability in different forms and biological methane consumption in freshwater systems is poorly understood. Here, we present high-resolution profiles of MOB abundance and pMMO and sMMO functional genes in relation to copper, methane and oxygen profiles across the oxic-anoxic boundary of a stratified lake. We show that even at low nanomolar copper concentrations, MOB species containing the gene for pMMO expression are present at high abundance. The findings highlight the importance of copper as a micronutrient for MOB species and the potential usage of copper acquisition strategies, even under conditions of abundant iron, and shed light on the spatial distribution of these microorganisms.

Highlights

Aerobic methane-oxidizing bacteria (MOB) are phylogenetically diverse and mainly group among the Alpha- and Gammaproteobacteria (α-MOB and γ-MOB) and the Verrucomicrobia
It has recently been proposed that methanobactin works in concert with a protein called MmoD to modulate the Cu-switch of soluble MMO (sMMO) and pMMO15, other proteins are involved in the Cu or Cu-methanobactin uptake and/or the Cu-switch in MOB16–20
In order to improve our understanding of CH4 and Cu dynamics in-situ, we studied seasonally stratified Rotsee, a small freshwater lake (1 km2) with pronounced sedimentary CH4 production and aerobic CH4 oxidation in its water column[24]

Summary

Introduction

Aerobic methane-oxidizing bacteria (MOB) are phylogenetically diverse and mainly group among the Alpha- and Gammaproteobacteria (α-MOB and γ-MOB) and the Verrucomicrobia. They efficiently mitigate the emission of methane (CH4) generated in freshwater systems while utilizing CH4 as their sole carbon and energy source[1]. Copper (Cu) has a regulatory effect on MOB activity, especially on the biosynthesis of the pMMO and sMMO enzymes and switching between these in cells able to express both[7]. In cells grown under sMMO expressing conditions, low but detectable levels of pMMO transcription have been measured[9,10]. We explore the hypothetical link between the depth distribution patterns of different Cu fractions and the abundance of MOB and their functional genes

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