Biology subjects

Zygadlowska, O. M.

Publications and source records attributed to Zygadlowska, O. M..

3 recordsLinked to original sources

bioRxiv2025

Seasonal dynamics of nitrification in the water column of marine Lake Grevelingen

Coastal ecosystems serve as vital connectors between land and ocean, and their nitrogen cycle and ammonium removal can be affected by various factors. During our seasonal sampling campaign in 2021, the eutrophic marine Lake Grevelingen exhibited high ammonium concentrations and low nitrification rates in the water column, except for a brief period in late summer. Our study revealed ammonium accumulation in the anoxic middle and bottom water layers due to restricted transport caused by water column stratification. Only when ammonium reached the oxic part of the water column, was a short-lived peak in nitrification activity and nitrifier abundance observed at the end of August. Amplicon sequencing indicated very low abundances of Nitrosococcus and Nitrospira (<0.2%) in March, while Nitrosomonas and Nitrospina peaked at the end of August with relative abundances of 2.5% and 1.3%, respectively. Archaea and archaeal ammonium oxidizers were found in very low abundances. Anammox 16S rRNA genes were not detected. Together, these observations suggest a limited role for nitrification in ammonium removal in marine Lake Grevelingen.

microbiology↗

bioRxiv2024

A ubiquitous and diverse methanogenic community drives microbial methane cycling in eutrophic coastal sediments

Coastal areas are responsible for over 75% of global marine methane emissions and this proportion is predicted to grow due to an increase in anthropogenically induced eutrophication and deoxygenation. Prolonged periods of low oxygen and high organic matter input have been put forward to cause an imbalanced microbial methane cycle, as methane oxidation cannot keep up with methane production. However, it is still unclear what factors affect each process and which microorganisms are responsible. Here we show that methanogenic processes dominate microbial methane cycling in the anoxic sediments of marine Lake Grevelingen (NL) after summer stratification with bottom water anoxia. We observed a shallow and narrow sulfate-methane transition zone between 5 and 15 cm depth, with high methane concentrations (> 5 mM) below this zone. Methanogenesis was dominant over methanotrophy in all investigated layers as active methanogenesis potential was detected down to 60 cm below sea floor, but methane oxidation was only observed in a narrow section of the sulfate-methane transition zone. Based on amplicon sequencing and sediment incubations, we uncovered a metabolically and phylogenetically diverse methanogenic community with distinct niche separation in different sediment layers. ANME archaea and their putative syntrophic sulfate-reducing bacteria were restricted to a narrow zone and were co-occurring with the detected methane oxidation activity. Our results suggest that eutrophication and deoxygenation will further contribute to rising methane emissions in coastal areas, as the microbial methane cycle will be tilted towards increased methanogenesis while the efficiency of the microbial methane filter is expected to decline.

microbiology↗

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↗