Biology subjects

Wallenius, A. J.

Publications and source records attributed to Wallenius, A. J..

3 recordsLinked to original sources

bioRxiv2023

Seasonal dynamics of the microbial methane filter in the water column of a eutrophic coastal basin

In the water column of coastal waters, methane-oxidizing bacteria (MOB) can form a methane biofilter. This filter can counteract high benthic methane fluxes and thereby lower methane emissions to the atmosphere. Recent metagenomic studies revealed that the metabolism of the MOB in the filter is versatile, and could quickly respond to changing oxygen concentrations. Changes in oxygen availability in coastal basins are largely driven by seasonal stratification and mixing. However, it is still unclear how well the methane biofilter functions throughout the seasons, and how this relates to MOB community composition. Here, we determined water column methane and oxygen depth profiles and the methanotrophic community structure, methane oxidation potential, and methane fluxes of the Scharendijke basin in marine Lake Grevelingen between March and October 2021. In this period, the methane filter mainly consisted of three MOB belonging to Methylomonadaceae. Although in low relative abundance, the methanotrophic community was present in the mixed water column in March and had increased to 9 % by July in the stratified water column, with a distinct vertical niche partitioning in the redoxcline. The methane and oxygen gradients were vertically decoupled in summer upon the formation of a suboxic zone. Surprisingly, this did not affect the vertical distribution or potential methane oxidation of MOB. Moreover, water-air fluxes remained below 0.6 mmol m-2 day-1. Our findings suggest active methane removal by MOB in virtually anoxic water. Weakening of the stratification in September resulted in higher diffusive methane fluxes to the atmosphere (up to 1.6 mmol m-2 day-1). This was likely due to a faster supply of methane, but also a reduction of methane oxidation. Thus, despite the rapid adaptation and versatile genomic potential of the MOB community, seasonal water column dynamics significantly influence methane removal efficiency.

microbiology↗

bioRxiv2022

Versatile methanotrophs form an active methane biofilter in the oxycline of a seasonally stratified coastal basin

The potential and drivers of microbial methane removal in the water column of seasonally stratified coastal ecosystems and the importance of the methanotrophic community composition for ecosystem functioning are not well explored. Here, we combined depth profiles of oxygen and methane with 16S rRNA gene amplicon sequencing, metagenomics, and methane oxidation rates at discrete depths in a stratified coastal marine system (Lake Grevelingen, The Netherlands). Three amplicon sequence variants (ASVs) belonging to different genera of aerobic Methylomonadaceae and the corresponding three methanotrophic metagenome-assembled genomes (MOB-MAGs) were retrieved by 16S rRNA sequencing and metagenomic analysis respectively. The abundances of the different methanotrophic ASVs and MOB-MAGs peaked at different depths along the methane oxygen counter-gradient and the MOB-MAGs show a quite diverse genomic potential regarding oxygen metabolism, partial denitrification, and sulfur metabolism. Moreover, potential aerobic methane oxidation rates indicated high methanotrophic activity throughout the methane oxygen counter-gradient, even at depths with low in situ methane or oxygen concentration. This suggests that niche-partitioning with high genomic versatility of the present Methylomonadaceae might contribute to the functional resilience of the methanotrophic community and ultimately the efficiency of methane removal in the stratified water column of marine Lake Grevelingen.

microbiology↗

bioRxiv2022

Sulfide toxicity as key control on anaerobic oxidation of methane in eutrophic coastal sediments

Coastal zones account for significant global marine methane emissions to the atmosphere. In coastal ecosystems, the tight balance between microbial methane production and oxidation in sediments prevents most methane from escaping to the water column. Anthropogenic activities, causing eutrophication and bottom water deoxygenation, could disrupt this balance in the microbial methane cycle and lead to increased methane release from coastal sediments. Here, we combined microbiological and biogeochemical analyses of sediments from three sites along a bottom water redox gradient (oxic-hypoxic-euxinic) in the eutrophic Stockholm Archipelago to investigate the impact of anthropogenically-induced redox shifts on microbial methane cycling. At both the hypoxic and euxinic site, sediments displayed a stronger depletion of terminal electron acceptors at depth and a shoaling of the sulfate-methane transition zone in comparison to the oxic site. Porewater methane and sulfide concentrations and potential methane production rates were also higher at the hypoxic and euxinic site. Analyses of metagenome-assembled genomes and 16S rRNA gene profiling indicated that methanogens became more abundant at the hypoxic and euxinic site, while anaerobic methane-oxidizing archaea (ANME), present in low coverage at the oxic site, increased at the hypoxic site but virtually disappeared at the euxinic site. A 98% complete genome of an ANME-2b Ca. Methanomarinus archaeon had genes encoding a complete reverse methanogenesis pathway, several multiheme cytochromes, and a sulfite reductase predicted to detoxify sulfite. Based on these results, we infer that sulfide exposure at the euxinic site led to toxicity in ANME, which, despite the abundance of substrates at this site, could no longer thrive. These mechanistic insights imply that the development of euxinia, driven by eutrophication, could disrupt the coastal methane biofilter, leading to increased benthic methane release and potential increased methane emissions from coastal zones to the atmosphere.

microbiology↗