Discovery of a 3-in-1 microorganism turns textbooks upside down

The study of environmentally relevant microorganisms shows greater diversity than previously assumed

A team of researchers has shown that there is an incredibly high biodiversity of environmentally relevant microorganisms in nature. This diversity is at least 4.5 times greater than previously known. The researchers recently published their findings in prestigious journals Nature Communications and FEMS Microbiology Reviews.

The hidden world of microorganisms is often overlooked, although many climate-related processes are influenced by microorganisms, often associated with an amazing diversity of organisms. Classify Within the groups of bacteria and archaea (“archaebacteria”). 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 this as an energy source and render it harmless.

“These processes also play an important role in lakes, marshes, and even in the human intestine to maintain nature’s balance and health,” says Professor Michael Bester, Head of the Department of Microorganisms at the Leibniz DSMZ and a professor at the institute. Microbiology at Technical University Braunschweig. One study has examined the metabolism of one of these new microorganisms in more detail, revealing a multifunctionality that was previously unattainable.

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

Critical balance 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 related to the carbon and nitrogen cycles, which underscores its importance. It is mainly operated by sulfate-reducing and sulfur-oxidizing microorganisms. Globally, sulfate reducers divert about a third of the organic carbon that reaches the seafloor each year. In contrast, 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 creates “dead zones” where animals and plants can no longer survive. This causes not only economic damage, for example to fisheries, but also social damage by destroying important local recreational areas. It is therefore important to understand which microorganisms maintain sulfur cycle homeostasis and how they do so.

Published results show that the species diversity of sulfate-reducing microorganisms includes at least 27 phyla (strains). Previously, only six phyla were known. In comparison, there are 40 currently known phyla in the animal kingdom Vertebrates It belongs to only one phylum, Chordata.

A schematic representation of the degradation of plant pectin—either by sulfate reduction or by oxygen respiration in the recently discovered acidophilic bacteria. Credit: DSMZ

Newly discovered multifunctional bacterial species

The researchers were able to map one of these new “sulfate reducers” to the little-researched phylum Acidobacteria and studied it in a bioreactor.

Using the latest methods from environmental microbiology, they were able to demonstrate that these bacteria can obtain energy from sulfate reduction and breathe oxygen. These two pathways are usually mutually exclusive in all known microorganisms. At the same time, the researchers were able to show that sulfate-reducing acidobacteria can break down complex plant carbohydrates such as pectin – another previously unknown property of “sulfate reducers.”

The researchers thus turned textbook knowledge on its head. They showed that complex plant compounds can be degraded under oxygen exclusion, not only by a coordinated interaction between different microorganisms, as previously thought, but also by a single bacterial species via a shortcut.

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

Another new discovery is that these bacteria can use sulfate and oxygen for this purpose. Researchers at DSMZ and the Technical University of Braunschweig are currently investigating how the new findings affect the interaction between the carbon and sulfur cycles and how they relate to climate-related processes.

References:

“Oxygen respiration and polysaccharide degradation by sulfate-reducing acidophilic bacteria” by Stefan Dijksma and Michael Bester, October 10, 2023, Nature Communications.
doi: 10.1038/s41467-023-42074-z

“Global diversity and inferred ecophysiology of microorganisms with divergent sulfate/sulfate-reducing potential” by Mohi Diao, Stefan Dijksma, Elif Koksoy, David Kamanda Ngugi, Karthik Anantharaman, Alexander Lowe and Michael Bester, 05 October 2023, FEMS Microbiology Reviews.
doi: 10.1093/femsre/fuad058