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Revealed how sulfate-breathing bacteria get energy from sulfur



A team led by scientists at the Institute of Chemical and Biological Technology at the New University of Lisbon (ITQB-NOVA) has discovered the existence of a new intermediate in the process by which certain bacteria obtain energy from sulfur. Their results, published in the latest issue 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 given in microbiology textbooks.

This paper describes how bacteria that use sulfur compounds in the process of respiration produce energy to live, a process that has hitherto been described in three steps, and which, 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 an asymmetry of charges is created between the two sides of the membrane - an essential step for the production of energy in the breathing process, as recalled by Inês Cardoso Pereira, research coordinator.

For Inês Cardoso Pereira, with these results, "Textbooks will be revised (...) and so will the models used by other scientists." It is known that sulfate-reducing bacteria (a form of sulfur) live scattered in the environment 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 at which sulfur is processed as a marker to describe the atmosphere on Earth 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 to specifically inhibit the inflammatory action of bacteria in the gut.


The project that gave rise to these results was funded by FCT, the National Science Foundation (USA) and the Deutsche Forschungsgemeinschaft (Germany). Two of the authors received Studentships from FCT, as PhD student and post-doctoral researcher. The research group of Inês Cardoso Pereira is part of the R&D unit GREEN-IT - Biorecourses for Sustainability, of ITQB-NOVA, which obtained the classification of Very Good in the last evaluation of R&D units conducted by FCT (in 2013/14). 


Images from top to bottom: 

- ITQB researchers involved 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 exploited 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, the bacteria grown in the lab 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)