How blue-green algae manipulate microorganisms

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Cyanobacteria in high-density cultures. Picture: Alexander Kraus
Cyanobacteria in high-density cultures. Picture: Alexander Kraus
Research team at the University of Freiburg discovers a previously unknown gene that indirectly promotes photosynthesis

Cyanobacteria are also known as blue-green algae and are considered the "plants of the ocean" because they photosynthesize on a gigantic scale, produce oxygen and extract the greenhouse gas CO2 from the environment. To do this, however, they need other nutrients such as nitrogen. A team led by biologist Wolfgang R. Hess , Professor of Genetics at the University of Freiburg, has discovered a previously unknown gene that plays a central role in the coordination of nitrogen and carbon exchange: Cyanobacteria use it to indirectly control the growth of microorganisms that promote photosynthesis. "Our work shows that there are diverse, previously unknown interactions between even the smallest organisms in the environment and that a large number of previously unknown genes play a role in this," says Hess. The results have been published in the journal Nature Communications.

Balance between main nutrients

The amounts of carbon (CO2) and nitrogen available to plants, algae and cyanobacteria are not always the same. A physiologically relevant balance between these two main nutrients is of great importance for photosynthesis. Alexander Kraus , PhD student of Wolfgang R. Hess at the University of Freiburg, has now discovered and characterized a gene in cyanobacterial gene data that plays a key role in this context: The gene encodes a protein called NirP1. This is only produced when the cells detect a lack of carbon relative to the available nitrogen.

The protein is too small to act as an enzyme like many other proteins. However, in collaboration with Philipp Spät and Boris Macek from the Proteome Center at the University of Tübingen, the researchers discovered that NirP1 can bind tightly to an enzyme that would normally convert nitrite into ammonium. NirP1 prevents this and thus ensures that nitrite accumulates in the cell; this leads to massive further metabolic changes, which were investigated in detail in collaboration with Martin Hagemann’s team at the University of Rostock. Finally, the cyanobacteria begin to export nitrite into the environment. There, the additional nitrite stimulates the growth of beneficial microorganisms, i.e. a microbiome that is conducive to the photosynthesis of the cyanobacteria.

Suggestions for further research

According to Hess, the results offer suggestions for further research into the interactions between microorganisms and the role of the genes that control them, which were previously often unknown. "In addition, small protein regulators such as NirP1 could be used in the future in ’green’ and ’blue’ biotechnology for the targeted control of metabolism."

Facts overview:

    Original publication: Kraus, A., Spät, P., Timm, S., Wilson, A., Schumann, R., Hagemann, M., Macek, B., Hess, W. R.: Protein NirP1 regulates nitrite reductase and nitrite excretion in cyanobacteria. In: Nature Communications 15, 1911 (2024).
    DOI:­’024 -46253-4

  • Wolfgang R. Hess is Professor of Genetics at the Faculty of Biology at the University of Freiburg. His research interests include RNA biology using experimental and bioinformatic methods, microbial systems biology and the biology of native CRISPR systems and their application. Alexander Kraus is a PhD student at the University of Freiburg.
  • A network of researchers at the Universities of Freiburg, Tübingen and Rostock was involved in the discovery. The work was funded by the German Research Foundation (DFG) as part of the "SCyCode" project.