Symbiotic cyanobacteria in lichens

Cyanolichens are obligate symbioses between fungi and cyanobacteria. They occur in many types of environments ranging from Arctic tundra and semi-deserts to tropical rainforests. Possibly even a majority of their global species diversity has not yet been described. Symbiotic cyanobacteria provide both photosynthate and fixed nitrogen to the fungal host and the relative importance of these functions differs in different cyanolichens. The cyanobiont can either be the sole photosynthetic partner or a secondary symbiont in addition to a primary green algal photobiont. In addition, the cyanolichen thallus may incorporate a plethora of other microorganisms. The fungal symbionts in cyanolichens are almost exclusively ascomycetes. Nostoc is by far the most commonly encountered cyanobacterial genus. While the cyanobacterial symbionts are presently not readily identifiable to species, molecular methods work well on the generic level and offer practical means for identifying symbiotic cyanobacterial genotypes. The present diversity of lichen cyanobionts may partly reflect the evolutionary effects of their lichen-symbiotic way of life and dispersal.Peer reviewe