idw – Informationsdienst Wissenschaft
Nachrichten, Termine, Experten
Nachrichten, Termine, Experten
An international team of researchers led by the Max Planck Institute for Marine Microbiology has uncovered a hidden world of tiny partnerships thriving in wastewater treatment plants worldwide. The microscopic allies—specialized bacteria living inside single-celled hosts—play a surprising role in both cleaning water and potentially contributing to greenhouse gas emissions.
Wastewater treatment is essential for protecting public health and the environment. In sewage plants, a diverse microbial community removes pollutants from agricultural, industry and household wastewater. Most research has focused on free-living bacteria within this community, but a new study now reveals that microbial partnerships – bacteria living inside other microbes – are also widespread and active.
Microbes teaming up
A few years ago, a team of researchers around Jana Milucka from the Max Planck Institute for Marine Microbiology in Bremen, Germany, discovered peculiar bacterial symbionts that associate with ciliates, single-celled organisms that can be found everywhere where there is water. The symbionts supply their hosts with energy, much like how mitochondria power our own cells – an until then unprecedented association. The researchers’ data indicated that these organisms might be especially common in wastewater, so the team decided to investigate this further.
Common members of the wastewater microbiome
Analysing data from sewage plants all over the world, the scientists identified 14 new species of these endosymbiotic bacteria. “By performing denitrification, the bacteria contribute to nitrate removal, a key step in wastewater treatment. At the same time, they help their hosts generate energy by converting harmful nitrates into dinitrogen gas,” first author Louison Nicolas-Asselineau explains. The scientists detected these partnerships in up to half of the wastewater plants, suggesting they are a common but previously overlooked part of this ecosystem. And they might be even more abundant: “We see that the symbionts’ numbers fluctuate a lot over time within individual sewage plants, so it is possible we might have missed a few.”
A climate concern
Denitrifying endosymbionts, including the newly identified wastewater species, typically encode a complete denitrification pathway that enables them to respire nitrate all the way to dinitrogen gas (N2). Additionally, most of these endosymbionts also possess an enzyme called cytochrome-cbb3 oxidase that allows them to respire oxygen in addition to nitrate.
However, one species stands out: Candidatus Azoamicus parvus not only lacks the ability to breathe oxygen but it is also unable to further break down nitrous oxide (N₂O), an intermediate of the denitrification process. Instead of converting N2O into the harmless N2, it releases this potent greenhouse gas into the surrounding water. Nitrous oxide is 300 times more powerful than CO₂, and wastewater treatment is known to contribute to anthropogenic N2O emissions to the atmosphere.
Worryingly, this species is widespread in sewage plants globally. “This is the first time we have ever found a denitrifying endosymbiont that produces nitrous oxide and it happens to be the one that is most widely distributed in wastewater treatment plants,” says Jana Milucka, the study's senior author.
Why it matters
Wastewater treatment is one of the largest applications of microbiology, essential for the preservation of natural environments as well as human health. The microbial partnerships now described in the journal ISME Communications have been widely overlooked. “We were very surprised that denitrifying endosymbioses were so abundant and prevalent in wastewater, given the dynamic conditions and intense ecological pressures in these systems”, says Nicolas-Asselineau. “Our study highlights the need to better understand the microorganisms involved in the wastewater processes, as they might be the key to improving wastewater treatment and reducing its environmental impact.”
Louison Nicolas-Asselineau
Greenhouse Gases Research Group
Max Planck Institute for Marine Microbiology, Bremen, Germany
Phone: +49 421 2028-6462
E-mail: lnicolas@mpi-bremen.de
Dr. Jana Milucka
Greenhouse Gases Research Group
Max Planck Institute for Marine Microbiology, Bremen, Germany
Phone: +49 421 2028-6340
E-mail: jmilucka@mpi-bremen.de
Louison Nicolas-Asselineau, Daan R Speth, Linus M Zeller, Ben J Woodcroft, Caitlin M Singleton, Lei Liu, Morten K D Dueholm, Jana Milucka (2025): Occurrence and temporal dynamics of denitrifying protist endosymbionts in the wastewater microbiome, ISME Communications, Volume 5, Issue 1, January 2025, ycaf209
DOI: https://doi.org/10.1093/ismeco/ycaf209
https://mpi-bremen.de/en/Page6579.html
The endosymbiont Candidatus Azoamicus mariagerensis and its ciliate host under the fluorescence micr ...
Source: Linus Matz Zeller
Copyright: Max Planck Institute for Marine Microbiology
It was mostly a desk job: After collecting data from international datasets as well wastewater treat ...
Source: Hailey-Hannah Cottet
Copyright: Max Planck Institute for Marine Microbiology
Criteria of this press release:
Journalists
Biology, Environment / ecology, Geosciences, Oceanology / climate
transregional, national
Research results, Scientific Publications
English
The endosymbiont Candidatus Azoamicus mariagerensis and its ciliate host under the fluorescence micr ...
Source: Linus Matz Zeller
Copyright: Max Planck Institute for Marine Microbiology
It was mostly a desk job: After collecting data from international datasets as well wastewater treat ...
Source: Hailey-Hannah Cottet
Copyright: Max Planck Institute for Marine Microbiology
You can combine search terms with and, or and/or not, e.g. Philo not logy.
You can use brackets to separate combinations from each other, e.g. (Philo not logy) or (Psycho and logy).
Coherent groups of words will be located as complete phrases if you put them into quotation marks, e.g. “Federal Republic of Germany”.
You can also use the advanced search without entering search terms. It will then follow the criteria you have selected (e.g. country or subject area).
If you have not selected any criteria in a given category, the entire category will be searched (e.g. all subject areas or all countries).
