In the past 20 years, the term microbiome gained immense popularity. Yet, most people associate the term with the human gut microbiome, even though microbiomes exist beyond the confines of our body. This World Microbiome Day, Nandini Shome and Sarah Wettstadt dive into the microbiomes of aquatic environments and their impact on our planet and environment. #MicrobiologyEvents

Why are aquatic microbiomes important?

The so-called microbiome comprises all microorganisms living in a certain niche. Due to the diversity of microbial players, a microbiome can have diverse functions and capabilities, making it generally vital to the ecosystems it inhabits.

Especially, environmental microbiomes play critical and distinct roles in Earth’s interconnected biogeochemical and climatic systems. For example, glacial and river microbiomes actively participate in carbon fixation and organic matter decomposition.

Chemolithotrophic microbes in the soil below ice and glaciers metabolise the sulphur and iron components of rocks. This process sets nutrients free, which are then released into downstream ecosystems where they feed other organisms.

River microbiomes have also been shown to be sensitive to anthropogenic stresses. Because some of these microbial communities can degrade xenobiotics, any shift or even loss would have severe consequences for the environment.

The cryospheric microbiome

Microbial communities found in snow, ice, permafrost soil, and glaciers belong to the so-called cryospheric microbiome. Such environments make up about 20% of the Earth, and yet, they are one of the least understood microbiomes.

Even though the idea of a core cryospheric microbiome has been developed, many microbial members of it remain uncharacterised. This makes the cryospheric microbiome especially diverse and likely well-adapted, due to the constant stresses it faces in these harsh environments.

A study by Wunderlin et al. showed that the Swiss and Australian Alps harbour diverse bacterial communities belonging to 25 different phyla and varying by geography and altitude. The six most abundant phyla, Proteobacteria, Acidobacteria, Actinobacteria, Bacteroidetes, Cyanobacteria and Firmicutes, accounted for 72%–98% of the total relative abundance, with no single dominant organism.

Another study by Xing et al. in the Tibetan Plateau showed that different habitats along a glacier host unique bacterial communities. Glacial runoff and ice-marginal moraine contained the highest bacterial diversity, with the genus Flavobacterium dominating runoff samples and the genus Hymenobacter moraine samples. This suggests that the environmental conditions in each habitat shape the present communities.

The freshwater microbiome

Similar to their frozen counterparts, freshwater microbiomes have attracted a lot of interest. Freshwater microbiomes comprise diverse assemblages of microorganisms that are fundamental to biogeochemical cycling, ecosystem productivity, and water quality. These microbial communities exhibit complex interactions influenced mostly by environmental gradients, hydrological dynamics, and anthropogenic pressures.

In their study, Chen et al. reported that the core microbial community of a river in China consisted of 18 and 40 Operational Taxonomic units in winter and summer, respectively. By investigating dispersal as an important factor affecting bacterial community structure in rivers, they found that flow rate and seasons mainly impact community structure.

The microbial biofilm community was mainly composed of Cyanobacteria (35%) and Proteobacteria (30.5%). Microbial communities tended to cluster according to environmental habitats and sampling seasons. However, the biofilm communities were more distinct and thus seemingly more resilient to such variations.

The marine microbiome

Marine environments are unique and have drawn the attention of researchers across the globe. While some single-celled microbes swim freely in the ocean water, many microbial communities associate with bigger marine organisms, animals, or anthropogenic waste.

The plastisphere, in particular, has become a recent focus due to concerns regarding pathogens and the spread of invasive species. Microbes associated with plastic or microplastic particles harbour unique community structures, exhibit distinct metabolic capabilities, and potentially influence nitrogen cycling.

A study by Fortin et al. showed that the biofilm community structures on plastic particles change as the biofilm matures. This may be due to the particle encountering free microbes on its journey through the ocean.

In contrast, in the southern Pacific Ocean, protist communities are major contributors to global biogeochemical cycling. Sturm et al. found that their structure and diversity are influenced by latitudinal gradients and oceanographic fronts. They mainly identified diatom, flagellate, and dinoflagellate taxa in three different regions.

The microbiome of the European Baltic Sea has also become a focus of several studies as its low salinity makes it distinct and unique. It also plays important roles in biogeochemical cycles and host–microbiome interactions. Cable bacteria especially receive a lot of attention due to their metabolic capabilities and adaptive responses to salinity and water temperature.

Celebrating aquatic microbiomes

As we have seen, aquatic microbiomes are highly diverse, shaped by their habitats and environmental conditions. They have a huge impact on the biogeochemical cycles of our planet, the quality of our freshwater, and the cleanliness of beaches. That’s why we have all the more reasons to be grateful for their functions.

So, this Microbiome Day, let’s celebrate all the different microbiome communities that we encounter in our daily lives and help them stay strong!

About the authors

Nandini Shome is an environmental scientist specializing in water quality and public health. Since her PhD from Nanyang Technological University, Singapore, her work bridges laboratory precision with real-world impact, from tropical freshwater systems to UK water utilities. When not in the lab, she enjoys sharing her knowledge through writing, public speaking, and going on long day trips with her little one.

 
Dr Sarah Wettstadt is a microbiologist-turned science writer and communicator writing for professional associations, life science organisations and researchers from the biological sciences. She runs the blog BacterialWorld to share the diverse and colourful activities of microbes and bacteria, based on which she co-published the colouring book “Coloured Bacteria from A to Z“. As science communication manager for the Scientific Panel on Responsible Plant Nutrition and blog post commissioner for the FEMSmicroBlog, Sarah writes about microbiology and environmental topics for various audiences. To help scientists improve their science communication skills, she co-founded SciComm Society, through which she offers guides, webinars and 1-on-1 coaching. Prior to her science communication career, Sarah completed a PhD at Imperial College London, UK, and a postdoc at the CSIC in Granada, Spain. In her non-scicomm time, she enjoys playing beach volleyball on the sunny beaches in Spain or travelling the world.

The section #MicrobiologyEvents for the #FEMSmicroBlog reports about events and meetings relevant to our network. These include world awareness days, FEMS-sponsored meetings or meetings of Member Societies and many more.

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