Polyextremotolerant black fungi: oligotrophism, adaptivepotential, and a link to lichen symbioses.

Blackmeristematicfungicansurvivehighdosesofradiationandareresistanttodesiccation.Theseadaptationshelpthemtocolonizeharsholigotrophichabitats,e.g.,onthesurfaceandsubsurfaceofrocks.Oneoftheirmostcharacteristicstress-resistancemechanismsistheaccumulationofmelanininthecellwalls.This,productionofotherprotectivemoleculesandaplasticmorphologyfurthercontributetoecologicalflexibilityofblackfungi.Increasedgrowthratesofsomespeciesafterexposuretoionizingradiationevensuggestyetunknownmechanismsofenergyproduction.OtherunusualmetabolicstrategiesmayincludeharvestingUVorvisiblelightorgainingenergybyformingfacultativelichen-likeassociationswithalgaeorcyanobacteria.Thelatterisnotentirelysurprising,sincecertainblackfungallineagesarephylogeneticallyrelatedtocladesoflichen-formingfungi.Similartoblackfungi,lichen-formingfungiareadaptedtogrowthonexposedsurfaceswithlowavailabilityofnutrients.Theyalsoefficientlyuseprotectivemoleculestotoleratefrequentperiodsofextremestress.Traitssharedbybothgroupsoffungimayhavebeenimportantinfacilitatingtheevolutionandradiationoflichen-symbioses.