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Bacterial Energy Metabolism Laboratory

Microorganisms are the main players in the biogeochemical cycling of elements that sustains Life in our planet. Over the history of Earth microbial metabolism led to profound changes in the redox conditions of the planet, the most dramatic of which was the gradual oxygenation of the atmosphere that set the stage for the appearance of multicellular eukaryotes. In the early Earth the atmosphere was anoxic and the first living organisms lived by anaerobic respiration, a type of bioenergetic metabolism in which an organic or inorganic compound is used as terminal electron acceptor instead of oxygen. Nowadays, an astounding number of microorganisms also live in anoxic or microoxic environments like soils, sediments or the human/animal gut, where they play essential roles in the ecosystem and our health.
 
The recent revolution of omics, meta-omics and imaging studies has provided a giant leap forward in our understanding of “who is where, doing what and how”, making these very exciting times in the study of Environmental Microbiology. These advances go hand-in-hand with a much better appreciation of how environment-microbe, microbe-microbe and host-microbe interactions operate, giving us new tools to exploit these interactions for Health, Environmental and Biotechnological Applications.
 
The respiratory chains of aerobic organisms are quite conserved in terms of proteins involved and mode of operation, which contrasts with the respiratory chains of anaerobic organisms that show a great diversity and versatility. This makes them an interesting and exciting topic to study, which widens our understanding of different biological strategies to support respiration.
 
The BEM group studies environmental microorganisms that grow by Anaerobic Respiration. We have focused mainly on investigating the bioenergetic processes that enable a large group of bacteria to respire sulfur compounds (like sulfate and sulfite). These bacteria are ancient organisms that are nowadays ubiquitously found in the environment and in animal guts. They play a key role in the biogeochemical cycles of Sulfur and Carbon, because sulfate is such a highly abundant anion in the environment (accumulating in the oceans). In addition, reduction of sulfate to hydrogen sulfide, and associated pyrite (FeS2) buryal, is a process that has an important contribution to the oxygenation of the atmosphere over geological timescales. For these reasons sulfate reducing bacteria (SRB) have a huge impact on the biogeochemistry of our planet. In the gut, these bacteria and closely associated sulfide-producing organisms are normal members of the colonic flora, but can have a pro-inflammatory role that may lead to colitis, inflammatory bowel diseases and cancer in genetically susceptible individuals.
 
Sulfate respiration is an ancient metabolism that displays some unique and interesting features, but how it is linked to energy conservation has not been clearly established. We seek to understand the respiratory metabolism of these organisms, which will give us important clues into the evolution of Life in the early earth, and is also essential for isotopic studies tracing the evolution of oxygen levels in the atmosphere over geological timescales. One of the important areas in our lab has been the study of membrane complexes of SRB. We isolated and characterized several of these complexes for the first time, which was an important breakthrough into understanding the mechanism of sulfate reduction. Ongoing studies focus on how these complexes interact with other proteins in metabolic pathways to achieve energy conservation.

 

SRB are currently the focus of intensive research to investigate their use as agents for the bioremediation of polluted anaerobic sediments, namely in the decontamination of toxic metals and radionuclides as well as of aromatic and chlorinated compounds. On the other hand, the reduction of sulfate may be environmentally detrimental as it results in the prodution of sulfide that is extremely toxic and corrosive. SRB can thus have a strong impact in any environment where organic matter is available in association with sulfate. In economic terms, SRB have very negative consequences in the oil and gas industry since they are a major cause of  biocorrosion and oil and gas souring.

However, the metabolism of these organisms can also be explored for beneficial applications. We have been studying their use as hydrogen producers for potential use in second stage dark fermentation processes.

SRB are also found in the human colon (an anaerobic environment), where they act as terminal oxidisers using the products of the fermentative bacteria metabolism (like hydrogen and short-chain fatty acids) as energy source and reducing sulfate or some alternative electron acceptor. It is thought that in some people with a genetic predisposition, the sulfide produced by sulfate respiration may cause or exacerbate inflammatory bowel diseases like ulcerative colitis or Crohn’s disease.

 

 

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Explore the powerful hydrogen metabolism of SRB and its hydrogenases, to develop cell-based systems metabolically engineered for H2 production, as well as hydrogenases with high activity and O2 tolerance, for practical applications.

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