Algal blooms are recurring events that sequester large amounts of carbon dioxide. Microalgae produce nearly half of the oxygen on our planet, making them key players in the global carbon cycle and thus in combatting the climate crisis. The study “Marine particle microbiomes during a spring diatom bloom contain active sulfate-reducing bacteria” in FEMS Microbiology Ecology analysed how microbial communities contribute to the global carbon cycle during a 2018 North Sea spring bloom. #FascinatingMicrobes
Amplicon sequencing reveals a network of organisms
Algal aggregates are composed of a diverse microbiome containing aerobic and heterotrophic bacteria. These degrade complex algal organic matter, hence the interactions between algae and bacteria seem to be crucial for the metabolic functions of algal blooms.
Since it is estimated that over 90% of algal-produced carbon is consumed by their associated bacteria, their interactions are important for the carbon sink function of algal aggregates. To shed light on the microbial compositions of a phytoplankton bloom in the southern North Sea, the study “Marine particle microbiomes during a spring diatom bloom contain active sulfate-reducing bacteria” in FEMS Microbiology Ecology relied on amplicon sequencing.
For this, samples from almost every day of a 2-months-period were analysed and the 18S and 16S rRNA genes sequenced. Based on highly conserved DNA sequences in eukaryotes (18S) and prokaryotes (16S), the resulting high-resolution information allowed to model the development of the microbial community over the course of the bloom. Computational analysis visualized the temporal co-occurrence of identified organisms as a network.
The temporal analysis revealed three major microbial clusters. Among them, Desulfobacterota stood out, as these are not known to be common members of microbial communities in the photogenic zone.
Furthermore, they co-occurred with diatoms but not with dinoflagellates. However, as this network shows temporal correlations and not physical connections, it is no proof that diatoms and Desulfobacteria actually interact.
Metaproteomic analysis offers insights into microbial activity
While genomic analysis reveals the composition of microbial communities, they do not provide information about the functional activity of the identified organisms. This is where metaproteomics comes in.
Shotgun metaproteomics uses mass spectrometry to identify proteins within a sample. This provided information about the functions actively performed by microbial communities at the sampled time point.
The abundance of bacterial proteins was much lower than that of eukaryotic proteins. Based on extensive computational analysis, the study identified proteins produced by the Desulfobacterota, including key enzymes of sulfur metabolism.
Anaerobic bacterial activity can support storing carbon dioxide
So far, only a few studies have identified Desulfobacterota in microbial communities during algal blooms. Since microalgae are known to produce oxygen, this creates toxic environments for anaerobes like Desulfobacterota.
However, as algal aggregates become larger, they start sinking to the bottom of the ocean. The theory is that this could lead to conditions where little oxygen becomes available within the aggregate. Inside these anaerobic niches, anaerobic microbes may be able to survive.
This study shed light on a new bacterial taxon that seems to play an important role in the carbon-sinking function of our oceans. While the sulfur metabolism of Desulfobacterota is likely a key metabolic feature of algal blooms, this finding requires further understanding to put it in the grand picture of ocean ecology and health.
- Read the article “Marine particle microbiomes during a spring diatom bloom contain active sulfate-reducing bacteria” by Siebers et al. in FEMS Microbiology Ecology (2024).
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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