Endolithic biofilms: a model for extraterrestrial ecological niches?

In natural ecosystems, bacteria, unicellular algae, filamentous and yeast-like fungi are often organized in thin films attached to or entrenched in substrata such as surfaces of solid rocks, minerals or larger organisms. Frequently the formation of a biofilm is the most successful survival strategy. Especially within endolithic biofilms micro-organisms actively create a safe niche to avoid extreme and thus harmful environmental conditions such as electromagnetic radiation, mechanical abrasion, water and temperature stress and hazardous chemical agents. Exemplary survival strategies are presented for bacteria, ascomycetes and green algae. On substrata without organic carbon sources, biofilms are composed of chemolithotrophic or phototrophic primary producers and heterotrophic organisms (including destruents).