Methodologies and Techniques for Detecting Extraterrestrial ( Microbial ) Life

Abstract

So far mainly spores or other “differentiated-for-survival” structures were considered to be resistant against extreme environmental constraints (including extraterrestrial challenges). Mi- crocolonial fungi (MCF) are unique growth structures formed by eukaryotic microorganisms inhabiting rock varnish surfaces in terrestrial deserts. They are here proposed as a new ob- ject for exobiological study. Sun-exposed desert rocks provide surface habitats with intense solar radiation, a scarce water supply, drastic changes in temperature, and episodic to spo- radic availability of nutrients. These challenging conditions reduce the diversity of life to MCF, whose resistance to desiccation and tolerance for ultraviolet (UV) radiation make them survival specialists. Based upon our studies of MCF, we propose that the following mecha- nisms are universally employed for survival on rock surfaces: (1) compact tissue-like colony organization formed by thermodynamically optimal round cells embedded in extracellular polymeric substances, (2) the presence of several types of UV-absorbing compounds (melanins and mycosporines) and antioxidants (carotenoids, melanins, and mycosporines) that convey multiple stress resistance to desiccation, temperature, and irradiation changes, and (3) intra- cellular developmental mechanisms typical for these structures.