Cities built on natural wetlands harbour huge depositories of stored carbon. Due to urban activities, methanogenic microbes convert the carbon into methane which is released into urban water canals. The study “Methanotrophic potential of Dutch canal wall biofilms is driven by Methylomonadaceae” in FEMS Microbiology Ecology analysed how microbial communities in canal biofilms impact methane levels in the water, as explained by Koen Pelsma and Cornelia Welte in this #FEMSmicroBlog entry. #MicrobiologyIsEverywhere
Biofilms in urban canals
Canals in cities such as Amsterdam (The Netherlands), Bangkok (Thailand), Hue (Vietnam), and Miami (USA) are excellent for studying the microbes producing and consuming methane. As an example within Europe, Dutch cities were built on wetlands of the Rhine and Meuse River delta.
Naturally, wetlands store a lot of carbon due to anaerobic conditions and sequestration of carbon dioxide by vegetation. Yet, building cities on wetlands and urban development drastically alters the environment and ecological balance.
These environmental changes provide the right conditions for methanogenic archaea to grow which thus convert the carbon within the organic matter into methane. This microbial activity leads to an increased emission of the greenhouse gas into the atmosphere.
Water canal biofilms consume methane
Microbial biofilms grow on the walls of canals around Amsterdam. These biofilms usually start at the water-air interface, with some being covered in mosses and other plants.
Surprisingly, these canal wall biofilms have the potential to metabolise methane – they are methanotrophic. One methanotroph bacterium from the Methyloglobulus genus could be identified as the key player within the canal ecosystem.
The study “Methanotrophic potential of Dutch canal wall biofilms is driven by Methylomonadaceae” in FEMS Microbiology Ecology aimed to shed light on the question of whether microbial biofilms on canal walls could offset methane emissions from urban canals. For this, samples were taken from canal wall biofilms across the Netherlands and methane emissions quantified with the help of a floating chamber.
The work showed that microbial biofilms on canal walls in several cities are methanotroph, while almost all canals emit methane regardless of season. In the city of Zwolle, biofilm methanotrophy was prevalent and its canals had the highest methane emissions.
In Leiden, the canals emitted methane, but biofilms on canal walls showed no methanotrophic activity. Also, the sampling site in Middelburg did not show methanotrophic activities. Canal water in Middleburg is saline, presumably preventing methanotrophic microbes from colonizing the canal wall biofilms.
However, canal waters in Middelburg do not emit methane, pointing to the fact that methane produced in the sediment is taken up by sediment methanotrophs. For the oxidation of methane under anaerobic conditions in the sediment, these methanotrophic microbes would use sulphate instead of oxygen. However, this was not followed up in the study.
Canal wall biofilms with methanotrophic potential
The study identified methanotrophs from the families Crenothrix, Methyloglobulus, and Methylomonadaceae across several sampling sites. These aerobic methanotrophs are common drivers of methane consumption by canal biofilms. At one site in Zwolle, more than 10% of the canal wall bacterial community consisted of either of these two strains. In contrast, both methanotrophy and methanotroph microbes were totally absent in samples from Leiden and Middelburg.
Even though water canal environments seem similar, their methanotrophic activities can be largely different, rendering the methane cycle of urban canals rather complex. The study thus sheds light on the different aspects of canal ecological systems with the goal of reducing the emission of greenhouse gas methane.
- Read the article “Methanotrophic potential of Dutch canal wall biofilms is driven by Methylomonadaceae” in FEMS Microbiology Ecology by Pelsma et al. (2023).
Koen A.J. Pelsma is a PhD candidate in environmental microbiology at Radboud University (The Netherlands). His research focuses on the microbial ecology of methane emissions from urban waterways, specifically the canals in Dutch cities. By integrating chemical and biological techniques, his goal is to better understand the influence of microbes on engineered environments.
Cornelia U. Welte is an Associate Professor in Microbiology at Radboud University (The Netherlands) since 2015. She obtained her PhD in 2011 on the biochemistry of methanogens at Bonn University (Germany). Her current research group investigates microbial methane cycling and pollutant bioremediation. Her research has been awarded with several prizes and prestigious awards such as the Research Award by the German Society of Microbiology (VAAM) in 2022.
About this blog section
The section #FascinatingMicrobes for the #FEMSmicroBlog explains the science behind a paper and highlights the significance and broader context of a recent finding. One of the main goals is to share the fascinating spectrum of microbes across all fields of microbiology.
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