Bacterial Energy Metabolism Laboratory
The key players in Bioenergetic Metabolism are membrane-bound protein complexes, which are involved in chemiosmotic energy conservation. Membrane proteins constitute approximately 25% of all proteins and play essential roles in cellular metabolism. However, they are technically very difficult to handle and thus are challenging targets to work with. Due to the complexity and intrinsic difficulty of studying membrane complexes it is useful to use bacterial model systems. This has also the advantage that bacterial respiratory chains are far more flexible and diversified than those of eukaryotic organisms, thus providing several interesting case studies of how nature developed different membrane protein complexes and mechanisms to achieve energy transduction.
The BEM group has focused on bacteria that grow by Anaerobic Respiration, a type of energy metabolism in which an organic or inorganic compound is used as terminal electron acceptor instead of oxygen. Currently, we investigate the molecular basis of the processes that enable a large group of bacteria to respire sulphur compounds (like sulfate and sulfite). These bacteria are ancient organisms that existed long before the appearance of oxygen on Earth, and which are ubiquitously found in the environment and in animal guts. They are implicated in a range of environmental and health issues, and are important research targets in the areas of Bioremediation, Biological Hydrogen Production, Microbial Fuel Cells, Biocorrosion, and Waste Treatment.
The respiratory chain of sulfate-reducing bacteria (SRB) is very distinct from other organisms, and the mechanisms of energy conservation, which have not been clearly established, involve several novel respiratory membrane complexes. We have been studying these membrane complexes and their role in the respiratory chain, as well as proteins involved in H2 metabolism. In addition, we are also interested in the role played by these bacteria within the human intestinal flora.
By studying the respiratory metabolism of SRB we aim to contribute to a better development of their biotechnological applications as well as to a better control of their biological activity, including potentially adverse health and environmental effects.
There are two main lines of research in the BEM lab:
1. Study of the energy metabolism in SRB, including investigation of the role of membrane complexes and the metabolic network involved in sulfate respiration.
2. 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.
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, that widens our understanding of different biological strategies to support respiration.
Nitrate and sulfate reducing bacteria are widely distributed in the environment, where they have a very important impact. The biological reduction of nitrate and nitrite provides a means of removing these polluting anions from the environment, producing nitrogen N2 (in the case of denitrifying bacteria) or ammonium (in the case of ammonifying bacteria) which can be assimilated by living organisms. The reduction of sulfate by sulfate reducing bacteria (SRB) is a major step in the biogeochemical sulfur cycle, and has also a major contribution to the carbon cycle in anaerobic environments. 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 (as for example in sea water which contains a high concentration of 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.
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.
Another interesting aspect of SRB is that they have a very active hydrogen metabolism, which can be used as the sole energy source, or formed as a metabolic product during fermentative growth in the absence of sulphate. Hydrogen may also be involved as an intermediary in the sulfate respiratory process. These bacteria produce large amounts of very active hydrogenases, enzymes that are natural micro-reactors for the production and/or consumption of H2. The study of these proteins is crucial to direct metabolic engineering aimed at a sustained biological production of hydrogen, the clean energy vehicle for the future. In particular, a [NiFeSe] hydrogenase from these organisms has a strong biotechnological potential because it has a very high hydrogen production activity and is tolerant to oxygen.