News from 'black belt' masters of symbiosis

The reputation of lichens as extremotolerant organisms is built ontheir occurrence in habitats where most other eukaryotes find itdifficult to survive. Lichens withstand recurrent cycles of desicca-tion and re-wetting in their environments by reverting to a statewithout active signs of life during periods of drought, yet they areable to resume metabolism quickly with appropriate levels ofhydration. In this stage, a substrate's conditions, includingchemistry, pH level, and water availability, determine thecomposition of lichen species in different habitats. Their sensitivityin metabolically active stages also explains the use of lichens as fine-tuned bioindicators of environmental conditions.