Abstract
Psychrophilic microorganisms have successfully colonized all permanently cold environments from the deep sea to mountain and polar regions. The ability of an organism to survive and grow in cryoenviroments depends on a number of adaptive strategies aimed at maintaining vital cellular functions at subzero temperatures, which include the structural modifications of the membrane. To understand the role of the membrane in the adaptation, it is necessary to characterize the cell-wall components, such as the lipopolysaccharides, that represent the major constituent of the outer membrane. The aim of this study was to investigate the structure of the carbohydrate backbone of the lipooligosaccharide (LOS) isolated from the cold-adapted Psychrobacter arcticus 273-4. The strain, isolated from a 20,000-to-30,000-year-old continuously frozen permafrost in Siberia, was cultivated at 4 °C. The LOS was isolated from dry cells and analyzed by means of chemical methods. In particular, it was degraded either by mild acid hydrolysis or by hydrazinolysis and investigated in detail by 1H and 13C NMR spectroscopy and by ESI FT-ICR mass spectrometry. The oligosaccharide was characterized by the substitution of the heptose residue, usually linked to Kdo in the inner core, with a glucose, and for the unusual presence of N-acetylmuramic acid.
Highlights
Cold environments are arguably the most widespread on our planet and in our solar system [1].At least 80% of terrestrial habitats and oceans are permanently cold, together with six of the other eight planets of our solar system
We report the structural characterization of the carbohydrate backbone of the LOS of Psychrobacter arcticus 273-4 grown at 4 °C
Psychrobacter arcticus strain 273-4 cells were grown at 4 °C and removed from the medium by centrifugation
Summary
Cold environments are arguably the most widespread on our planet and in our solar system [1]. At least 80% of terrestrial habitats and oceans are permanently cold, together with six of the other eight planets of our solar system. Understanding life’s adaptation to cold environments on our planet could be useful in the search for and understanding of life on other planets [2]. Many microorganisms populate Arctic and Antarctic regions [3], and those inhabiting permafrost in particular are good candidates to study cold-adaptation, due to the mean annual temperature between. One physiological response to the cold environment is the alteration of membrane components, such as the presence of unsaturated and branched fatty acids in phospholipids that maintain membrane fluidity [8], and the different phosphorylation of membrane proteins and lipopolysaccharides [9,10,11,12,13,14]
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