Iron-scytonemin complexes: DFT calculations on new UV protectants for terrestrial cyanobacteria and astrobiological implications

Cyanobacterial colonies produce the radiation-protectant biomolecule scytonemin as part of their response strategy for survival in environmentally stressed conditions in hot and cold deserts. These colonies frequently use sandstone rocks as host matrices for subsurface colonization, which is accompanied by a zone of depletion of iron and transportation of iron compounds to the mineral surface. It is suggested that an iron-scytonemin complex could feature in this survival strategy and facilitate the movement of iron through the rock. Calculations were carried out on several hypothetical iron-scytonemin complexes to evaluate the most stable structure energetically and examine the effect of the complexation of the biomolecule upon the electronic absorption characteristics of the radiation-protectant species. The implications for extraterrestrial planetary detection and analytical monitoring of an iron-scytonemin complex are assessed.