Functional biomolecules of Antarctic stromatolitic and endolithic cyanobacterial communities

For activity and survival in extreme terrestrial Antarctic habitats, lithob iontic cyanobacteria depend on key biomolecules for protection against envi ronmental stress and for optimization of growth conditions. Their ability t o synthesize such molecules is central to their pioneering characteristics and major role as primary producers in Antarctic desert habitats. Pigmentat ion is especially important in protecting them against enhanced UVB damage during stratospheric ozone depletion (the Ozone Hole) during the Antarctic spring and subsequent photoinhibition in the intense insolation of the summ er. To be effective, especially for the screening of highly shade-adapted p hotosystems of cyanobacteria, protective pigments need to be located strate gically. Antarctic lithic cyanobacterial communities are therefore stratifi ed, as in soil biofilms of Alexander Island, the benthic stromatolitic mars of ice-covered hypersaline lakes in the McMurdo Dry Valleys, and the endol ithic communities within translucent Beacon sandstone outcrops of Victoria Land. The protective pigments include scytonemin, carotenoids, anthroquinon es and mycosporine-like amino acids. To detect and locate photoprotective p igments in situ in free-living cyanobacteria and cyanolichens from hot and cold desert habitats, we have used Fourier-transform Raman microspectroscop y. With appropriate power inputs for labile molecules, this high-precision, non-intrusive laser-based technique can not only identify biomolecules in their natural state but also locate them spatially within the habitat relat ive to the components of the community, which require protection In conjunc tion with direct and epifluorescence microscopy it provides a spatial and f unctional description of the protective strategy of a community. We present the unique Raman spectrum of scytonemin and use its primary and corroborat ive peaks to identify it within the plethora of other biochemical constitue nts of several natural cyanobacterial communities, including an Antarctic e ndolith. The remote-sensing aspect of this technique makes it suitable not only for spatial biochemical analysis of present and palaeontological Antar ctic communities but also for analogous putative habitats on Mars.