So-called rock-eating microorganisms obtain their energy to convert carbon dioxide (CO2) from inorganic sources and make up the vast majority of biomass producers. Using electron microscopy and infrared spectroscopy, a research team from the universities of Potsdam and Marburg has investigated the structure of DAB2 in the sulfur bacterium Halothiobacillus neapolitanus. Their findings have been published in Nature Communications.
Carbon dioxide (CO2) is a component of the atmosphere and provides the essential element for all life on Earth: carbon. Autotrophic primary producers – organisms such as cyanobacteria and plants that convert CO2 into complex carbohydrates using energy from sunlight – play a key role in the conversion of CO2. This process produces biomass in the form of glucose, starch, and cellulose.
Unlike primary producers, however, the majority of microorganisms do not derive their energy from sunlight but instead utilize inorganic sources such as H₂, CO₂, or various sulfur compounds. These bacteria are referred to as lithotrophic microorganisms or “rock eaters”.
Carbonic acid
When CO2 reacts with water, carbonic acid is formed, which breaks down into bicarbonate (HCO3–). CO2 spontaneously enters the bacterial cell and can also leave it again; the charged HCO3– molecule, on the other hand, cannot cross the cell membrane without an additional energy supply.
Normally, the breakdown of the molecule ATP provides the energy needed to transport HCO3– into the cell, but this is not the case in lithoautotrophic microorganisms. These organisms often inhabit extreme habitats and must not waste ATP. In these organisms, the DAB2 membrane complex ensures that HCO3– is produced directly from CO2 within the cell.
The research team from Potsdam and Marburg investigated the mechanism that enables DAB2 to selectively accumulate HCO3– within the cell in an ATP-independent manner.
Rock eaters
“Using electron microscopy, we examined the structure of DAB2 from the sulfur bacterium Halothiobacillus neapolitanus and were able to show that the carbonic acid reaction described above is coupled to the concentration gradient across the cell membrane,” says Emmy Noether group leader Dr. Jan Schuller from the University of Marburg. A concentration gradient as difference in particle concentration inside and outside the cell forms across the cell membrane due to the selective accumulation of charged particles, such as protons (H+). This represents a general principle of biological energy storage.
“Based on the spectroscopic data, we have developed a theory according to which lithoautotrophic microorganisms utilize the concentration gradient across the cell membrane to catalyze an ATP-independent conversion of CO₂ to HCO3–,“ adds Dr. Sven Stripp from the University of Potsdam, who leads a Heisenberg research group at the Institute of Chemistry. As a result, the energy metabolism of these microorganisms is highly efficient, enabling the rock eaters to build up biomass even under hostile conditions.
Link to Publication: Lo, Y.K., Seletskiy, M., Bohn, S., Deobald, D., Glatter, T., Stripp, S.T, Schuller, J.M. Structural basis of membrane potential coupled vectorial CO₂ hydration by the DAB2 complex in chemolithoautotrophs. Nat Commun 17, 4071 (2026). https://doi.org/10.1038/s41467-026-72558-7
No comments yet