Revealed how sulfate-breathing bacteria obtain energy from sulfur

A team led by scientists from the Institute of Chemical and Biological Technology at Universidade Nova de Lisboa (ITQB-NOVA) has discovered the existence of a new intermediate in the process by which certain bacteria obtain energy from sulfur. Their findings, published in the latest edition of the prestigious journal Science, unravel a long-standing mystery about the metabolism of so-called sulfate-reducing bacteria and challenge the description of the process found in microbiology textbooks.

This study describes how bacteria that use sulfur compounds in the respiration process produce energy to live, a process that has been described in three steps until now and, with this discovery, becomes four. The identification of this fourth intermediate, produced by the action of a protein located in the bacterial membrane, explains for the first time how a charge asymmetry is created between the two sides of the membrane—an essential step for energy production in the respiration process, as Inês Cardoso Pereira, research coordinator, points out.

For Inês Cardoso Pereira, with these results, "Textbooks will be revised (...) and the models used by other scientists will also be revised." It is known that sulfate-reducing bacteria (a form of sulfur) live scattered in environments where oxygen is scarce, such as marine sediments, and are therefore essential for the renewal of one of the most important biogeochemical cycles for life on Earth. Geochemists, who use the rate of sulfur processing as a marker to describe the Earth's atmosphere over geological time, will have to revise their mathematical models, as the existence of the new intermediate affects these calculations.

These bacteria are also present in our intestinal flora, which means that the new data presented by Portuguese scientists also has an impact on health, as it gives researchers a new target for specifically inhibiting the inflammatory action of bacteria in the intestine.

The project that led to these results was funded by FCT, the National Science Foundation (USA), and the Deutsche Forschungsgemeinschaft (Germany). Two of the authors received Studentships FCT, as a doctoral student and a postdoctoral researcher. Inês Cardoso Pereira's research group is part of the GREEN-IT – Biorecursos para a Sustentabilidade (Bioreources for Sustainability) R&D unit at ITQB-NOVA, which was rated Very Good in the latest evaluation of R&D units carried out by FCT ( in 2013/14). 

Images from top to bottom: 

–ITQB researchersinvolved in the work. From left to right: Fabian Grein, André Santos, Inês Cardoso Pereira, and Sofia Venceslau. 

– Detail of marine sediment (Ria Formosa, Algarve). In the area explored by the crab, the black color reveals the presence of sulfate-reducing bacteria.

– Colonies of sulfate-reducing bacteria in a Petri dish. As in their habitat, bacteria grown in the laboratory have a characteristic black color due to the presence of sulfide (the end product of these bacteria's respiration).

(Credits: Inês Cardoso Pereira and ITQB-NOVA)