Distribution of scytonemin in endolithic microbial communities from halite crusts in the hyperarid zone of the Atacama Desert, Chile

Abstract

Scytonemin, a UV-screening molecule produced by certain Cyanobacteria to protect against harmful UV radiation, was studied in endolithic cyanobacterial colonies in the halite crust from one of the driest places on Earth - the hyperarid zone of the Atacama Desert. The distribution of the pigment within the evaporitic crust was studied in detail by various independent analytical methods: Raman spectroscopy (including Raman imaging); advanced microscopic observations (fluorescence microscopy, confocal laser scanning microscopy, low-temperature scanning electron microscopy); and spectrophotometric analyses. The differences in scytonemin biosynthesis were mapped within the colonized interior layers, which can be divided into scytonemin-rich and scytonemin-poor zones. A 532 nm laser for excitation proved to be an ideal excitation source with which to observe the relative content of scytonemin within a particular cell aggregate, as well as between different cell aggregates; based on the scytonemin/carotenoid Raman signal intensity ratio of selected corroborative bands for these two compounds. Significantly, scytonemin was found to accumulate within a decayed biomass in the surface portions of the halite crust. These were found to be highly enriched in both the absolute scytonemin content (as documented by UV/VIS spectrophotometry) and its content relative to other pigments associated with the cyanobacterial cells (e.g. carotenoids and chlorophyll).

Extreme environments: microbiology leading to specialized metabolites

“…These lithic microbial communities have developed adaptive strategies to withstand the extreme environmental conditions that prevail in the Atacama Desert (Gómez‐Silva ), as is the case with similar communities in the Namib Desert (Stomeo et al ). It is evident that green hypoliths in the hyperarid core of the Atacama Desert are dominated by Chroococcidopsis and Nostocales species and red hypoliths by Chloroflexi (Lacap et al ), whereas Noctocophycideae and Synechococcophycideae species are present in lower numbers (Vítek et al ). Cyanobacteria also produce pigments which may protect them against lethal doses of UV‐radiation in hyperarid habitats (Powell et al ).…”

“…They produce pigments like scytonemin ( 23 ) and the mycosporine‐like amino acids shinorine ( 24 ) and porphyra‐334 ( 25 ) which may absorb potentially lethal doses of UV‐radiation found in hyperarid environments., these compounds are being evaluated as a source of potent sunscreens (Powell et al ). Scytonemin ( 23 ), which is produced by a Chroococcidiopsis strain, has potential as a chemical marker for endolithic cyanobacterial colonies in halite crusts which are common in the hyperarid zone of the Atacama Desert (Vítek et al ) . This compound is of considerable interest as it causes attenuation of mitogen‐induced inflammatory hyperproliferation through inhibition of polo ‐like kinase hence its unique dimeric structure may prove to be a potential scaffold for the development of potent kinase inhibitors (D’Orazio et al ).…”

CARS microscopy of scytonemin in cyanobacteria Nostoc commune

“…Planning the study of scytonemin by coherent anti‐Stokes Raman scattering (CARS) microscopy, we relied on the spectroscopic data proposed in the last two papers. Together with spectroscopy, the Raman imaging of cyanobacterial aggregates as a spectroscopic analytical method has been employed studying scytonemin biosynthesis as a survival strategy of the Cyanobacteria under extreme conditions like a desert . However, studying algae by Raman spectroscopy can encounter some difficulties such a fluorescence background .…”

Raman spectroscopic study of the Chromobacterium violaceum pigment violacein using multiwavelength excitation and DFT calculations

“…The family of scytonemins and their methylated and methoxylated derivatives are pigments of high relevance in stressed environments and in exobiology; here also, theoretical work helped to assign Raman bands [18]. Raman spectroscopy allows the detection of low levels of scytonemin in extremophilic organisms in samples originating from dry desert areas [19].…”