Methane oxidation in anoxic lake water stimulated by nitrate and sulfate addition

Abstract

Methanotrophic bacteria play a key role in limiting methane emissions from lakes. It is generally assumed that methanotrophic bacteria are mostly active at the oxic-anoxic transition zone in stratified lakes, where they use oxygen to oxidize methane. Here, we describe a methanotroph of the genera Methylobacter that is performing high-rate (up to 72 μM day −1 ) methane oxidation in the anoxic hypolimnion of the temperate Lacamas Lake (Washington, USA), stimulated by both nitrate and sulfate addition. Oxic and anoxic incubations both showed active methane oxidation by a Methylobacter species, with anoxic rates being threefold higher. In anoxic incubations, Methylobacter cell numbers increased almost two orders of magnitude within 3 days, suggesting that this specific Methylobacter species is a facultative anaerobe with a rapid response capability. Genomic analysis revealed adaptations to oxygenlimitation as well as pathways for mixed-acid fermentation and H 2 production. The denitrification pathway was incomplete, lacking the genes narG/napA and nosZ, allowing only for methane oxidation coupled to nitrite-reduction. Our data suggest that Methylobacter can be an important driver of the conversion of methane in oxygen-limited lake systems and potentially use alternative electron acceptors or fermentation to remain active under oxygen-depleted conditions.

Enhanced Adsorptive Bioremediation of Heavy Metals (Cd2+, Cr6+, Pb2+) by Methane-Oxidizing Epipelon

“…The chromium-augmented treatment showed only a 1.61-fold increase for the high methane as compared to near atmospheric methane treatment (6 ppm). The sequence analysis of the microbial community from lake Biwa, Japan [3,56], stratified eutrophic Swiss lakes [57] and Lacamas lake in Washington, USA [58] showed Type I methanotroph dominances, similarly to our findings in this study.…”

Impact of Electron Acceptor Availability on Methane-Influenced Microorganisms in an Enrichment Culture Obtained From a Stratified Lake

“…The most abundant methanotroph of Lacamas Lake, a seasonally stratified lake, is a Methylobacter species; it was detected in the oxic water column in the winter and in the microoxic oxycline and the anoxic hypolimnion in the summer (van Grinsven et al, 2019). In order to be able to further study the response of this methanotroph to different concentrations of oxygen and other electron acceptors, an enrichment culture was established.…”

“…Lacamas Lake, the source of the material used for our enrichment culture, contained uncultured Methylobacter species thriving in the oxic and anoxic water columns as well as in the microoxic oxycline (van Grinsven et al, 2019). Incubations with water column samples revealed that these bacteria oxidized large amounts of methane (72 µM day −1 ) under anoxic conditions in the stratified summer water column, stimulated by the addition of both nitrate and sulfate (van Grinsven et al, 2019), but were also naturally present in the oxic, methane-depleted winter water column. Phylogenetic analysis showed that the Methylobacter species of the Lacamas Lake summer and winter water columns and incubations grouped closely together with the Methylobacter species that dominated the enrichment culture (i.e., 96-99% similarity; Figure 1).…”

“…Previously, we showed that Methylobacter sp. is an important methanotroph in the seasonally stratified Lake Lacamas, and water column incubation experiments revealed that it is capable of methane oxidation under a variety of conditions (van Grinsven et al, 2019). Here, we describe the establishment of an enrichment culture dominated by Methylobacter and used it to evaluate the effects of the concentration of the potential electron acceptor (oxygen, nitrate, sulfate, and humic substances) on the methane oxidation rates and microbial community structure using 16S ribosomal RNA (rRNA) gene amplicon sequencing.…”

A Complex Interplay between Nitric Oxide, Quorum Sensing, and the Unique Secondary Metabolite Tundrenone Constitutes the Hypoxia Response in Methylobacter

“…consumption not only in oxic but also in hypoxic and even anoxic niches (9)(10)(11)(12), even though the mechanisms for such activity remain poorly understood, given the essential role of dioxygen in methane oxidation catalyzed by methane monooxygenase (MMO). The observations on the dominant nature of Methylobacter have also been supported by results from microcosm incubation experiments in which Methylobacter performed as the most competitive species, especially under low dioxygen tensions (13,14).…”