Discovery of a 3-in-1 Microorganism Upends Textbooks

Research into environmentally relevant microorganisms shows greater diversity than previously assumed.

A team of researchers has shown that nature contains an incredibly high biodiversity of environmentally relevant microorganisms. This diversity is no less than 4.5 times greater than previously known. The researchers recently published their findings in prestigious journals Nature communication and FEMS Microbiology Reviews.

The hidden world of microorganisms is often overlooked, even though many climate-relevant processes are influenced by microorganisms, often associated with an incredible diversity of kind within the groups bacteria and archaea (“primitive bacteria”). For example, sulfate-reducing microorganisms convert one-third of the organic carbon in marine sediments into carbon dioxide. This produces toxic hydrogen sulfide. On the plus side, sulfur-oxidizing microorganisms quickly use it as an energy source and render it harmless.

“These processes also play an important role in lakes, swamps and even in the human intestines to keep nature and health in balance,” says Prof. Michael Pester, Head of the Department of Microorganisms at the Leibniz Institute DSMZ and Professor at the Institute. of Microbiology at the Technische Universität Braunschweig. A study examined the metabolism of one of these new microorganisms in more detail, revealing multifunctionality previously unattainable.

Extremely high species diversity of sulfate-reducing microorganisms discovered. Sulfate reducers are now found in a total of 27 phyla within the Bacteria and Archaea instead of the six previously known. Credit: DSMZ

The critical equilibrium of the sulfur cycle

The sulfur cycle is one of the most important and oldest biogeochemical cycles on our planet. At the same time, it is closely linked to the carbon and nitrogen cycles, which underlines its importance. It is mainly caused by sulfate-reducing and sulfur-oxidizing microorganisms. On a global scale, sulfate reducers convert about a third of the organic carbon that reaches the seabed each year. In return, sulfur oxidizers consume about a quarter of the oxygen in marine sediments.

When these ecosystems become out of balance, the activities of these microorganisms can quickly lead to oxygen depletion and the buildup of toxic hydrogen sulfide. This leads to the formation of ‘dead zones’ where animals and plants can no longer survive. This not only causes economic damage, for example to fishing, but also social damage through the destruction of important local recreational areas. It is therefore important to understand which microorganisms keep the sulfur cycle in balance and how they do this.

The published results show that the species diversity of sulfate-reducing microorganisms spans at least 27 phyla (phyla). Previously, only six phyla were known. By comparison, there are currently 40 known phyla in the animal kingdom vertebrates belonging to only one phylum, the Chordata.

Schematic representation of the breakdown of plant pectin – both by sulfate reduction and by oxygen respiration in a newly discovered acidobacterium. Credit: DSMZ

Newly discovered multifunctional bacterial species

The researchers were able to assign one of these new ‘sulfate reducers’ to the little-researched strain of acidobacteriota and study it in a bioreactor.

Using advanced methods from environmental microbiology, they were able to demonstrate that these bacteria can obtain energy from both sulfate reduction and oxygen respiration. These two pathways are normally mutually exclusive in all known microorganisms. At the same time, the researchers were able to demonstrate that the sulfate-reducing acidobacteriota can break down complex plant carbohydrates such as pectin – another previously unknown property of ‘sulfate reducers’.

The researchers have therefore turned textbook knowledge upside down. They show that complex plant substances can be degraded under oxygen exclusion not only by the coordinated interaction of several microorganisms, as previously thought, but also by a single bacterial species via a shortcut.

Dr. Stefan Dyskma (left) and Prof. Dr. Michael Pester next to a bioreactor in the DSMZ, in which new “sulfate reducers” could be studied. Credit: DSMZ

Another new finding is that these bacteria can use both sulphate and oxygen for this. Researchers from the DSMZ and the Technische Universität Braunschweig are currently investigating how the new findings influence the interplay between the carbon and sulfur cycles and how they relate to climate-relevant processes.

References:

“Oxygen respiration and degradation of polysaccharides by a sulfate-reducing acidobacterium” by Stefan Dyksma and Michael Pester, October 10, 2023, Nature communication.
DOI: 10.1038/s41467-023-42074-z

“Global diversity and inferred ecophysiology of microorganisms with the potential for dissimilatory sulfate/sulfite reduction” by Muhe Diao, Stefan Dyksma, Elif Koeksoy, David Kamanda Ngugi, Karthik Anantharaman, Alexander Loy and Michael Pester, October 5, 2023, FEMS Microbiology Reviews.
DOI: 10.1093/femsre/fuad058