Bacterium (Halomonas titanicae) © OggiScienza / Flick, CC BY-NC
Bacterium (Halomonas titanicae) © OggiScienza / Flick, CC BY-NC
Science and technology
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Halomonas microorganisms are able to survive in extremely hostile salty environments, by accumulating the molecule ectoine to make up for the external salt concentration fluctuations. Neutron scattering experiments have offered up explanations as to how ectoine helps such bacteria to survive: it acts inside bacteria by maintaining the dynamic properties of water, which are essential for life. Published in Scientific Reports, this finding was obtained by a team of researchers chiefly from the Institut Laue-Langevin, CNRS, CEA, Université Grenoble Alpes, Max Planck Institute of Biochemistry and the biotechnology company Bitop. It sheds light on the way microbes adapt to extreme environments. The bacterium Halomonas harbours strong potential for biotechnological applications in the health, bioremediation and waste management sectors for example.
Microorganisms are the most ubiquitous life form on Earth, and understanding the way they behave is crucial for our own survival and well-being. Microbial life demonstrates an astonishingly agile ability to adapt to extreme environments – ensuring their survival in extremely hot or cold climates, acidic or basic environments, salty conditions like in the Dead Sea or under high pressure such as at great ocean depths, all conditions that would be harmful to complex organisms. These organisms are called extremophiles. Within this category, the bacteria isolated in saltmarshes or marine environments include a variety of interesting species with high biotechnological potential, not least the bacterium Halomonas titanicae, which was recently found in the hull of the sunken RMS Titanic liner. It is believed that the action of H. titanicae leads to a formation of knob-like rust mounds which could ultimately lead to the Titanic disintegrating into dust by 2030. Likewise, this bacterium has also been identified as a potential hazard for oil rigs and other offshore metal structures built by human hand. But this rusting property could also serve a useful purpose in bioremediation or waste management to speed up the decomposition of shipwrecks littering the ocean floor.

The experiments focused on the way ectoine interacts with water, proteins and membranes, and were conducted at the Institut Laue-Langevin (ILL), a world neutron science and technology leader, in partnership with the Max Planck Institute of Biochemistry (MPIB), the biotechnology company Bitop and Institut de biologie structurale (CEA/CNRS/Université Grenoble Alpes). Ectoine is a natural compound found in many organisms, including Halomonas. It acts as a protective substance in the same way as an osmolyte – a molecule which plays a role in maintaining cell volume and fluid balance – and thus helps organisms to thrive under extreme environmental stress. Ectoine is considered to be a compatible solute in that its presence within the cell does not interfere with the cellular metabolism and biochemistry. Halomonas can produce ectoine up to an intracellular concentration of 20% of the dry mass of the cell. This adaptive regulatory process means that the microorganism is halotolerant over a broad range of salt concentration, from 0.5 to 25% NaCl (sea water tends to have a salinity of around 3.5% on average). Because ectoine exhibits an indirect stabilising effect on proteins and membranes as well as a related inhibitory effect on mammalian cell inflammation, it has myriad applications in cosmetics and clinical practice thanks to its moisturising, stabilising and inflammation-reducing properties, including in the treatment of allergies, atopic dermatitis, coughs and cold symptoms.

Used in combination with isotopic labelling methods, neutrons have shown how ectoine acts by leaving the "shell" of water on protein and membrane surfaces intact – something which is essential for them to function biologically. H2O molecules in liquid water interact with each other through a highly dynamic fluid network of hydrogen bonds between the oxygen and hydrogen atoms of adjacent molecules. Other substances found in the water can hinder this organisation. Through the neutron-scattering experiments it was possible to describe the effects ectoine has on hydrogen bond dynamics and realise that the protective characteristics of ectoine do not interfere with cellular metabolism. For ectoine does not so much hinder as improve the remarkable dynamic properties of hydrogen bonds in water. Water is dependent on these hydrogen bonds for its solvent capabilities and they are vital for the proper organisation, stabilisation and functioning of proteins, lipids, membranes, RNA and DNA.

As Dr Joe Zaccaï, a CNRS emeritus scientist who works at the ILL, explains: "It is well-known that, guiding our searches for life on Mars, and elsewhere in the Universe I might add, is the search for liquid water – without which life forms cannot exist. Its remarkable properties lie in the dynamic hydrogen bond networks which are instrumental in macromolecular interactions and folding, forming the basis of proteins' biological functions. The findings of this study illustrate how the osmolyte behind the halotolerance response in microorganisms brings about compensating effects on the hydrogen bonds in the respect of essential biological properties. Neutrons are ideal for studying the structure and dynamics of water and biological molecules because of their unique advantages. These include a high penetrative power without causing any radiation damage to the sample and the possibility of labelling a structure by replacing the hydrogen with its deuterium isotope. Each of the instruments used in the study acted like a "giant microscope" of different magnification to enable us to ‘see’ the details, from the crucial formation of hydrogen bonds at the level of the atomic right up to the bigger protein and membrane structures. Ectoine may already have been the subject of extensive spectroscopic and thermodynamic research, but we are proud that, through its use of neutrons, ours is the first study to allow for direct experimental characterisation of ectoine-water-protein and ectoine-water-membrane structures as a means of explaining how this altogether fascinating and useful molecule works."

Publié le September 6, 2016
Mis à jour le February 14, 2017

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