Expanding the geographic and host range of moss-nostocacean symbioses in central Europe

Since their re-discovery, Moss-cyanobacterial symbioses are of increasing interest, especially Nostoc-feather moss symbioses. Efforts to document Nostoc-feather moss symbioses have historically been centered in Scandinavia and the North American Boreal forest zone. Herein we report the results of several opportunistic surveys investigating the occurrence of Nostocaceae-moss symbioses in the region of Franconia (Germany), from Hylocomium splendens of the forest floor and four moss species (Orthotrichum lyellii, Zygodon dentatus, Homalia trichomanoides, Pseudoamblystegium subtile) located on three tree species (Fagus sylvatica, Fraxinus excelsior, and Sorbus schuwerkiorum). Using culture- and microscopy-based methods, we confirm the occurrence of such symbioses in our region. Four new moss host species for the symbiosis are documented, from the epiphytic family Orthotrichaceae (Orthotrichum sp. and Zygodon sp.), and also Neckeraceae (Homalia trichomanoides) and Amblystegiaceae (Pseudoambylstegium subtile). This further extends the range of known moss hosts for Nostoc and Nostoc-related organisms outside the traditional feather moss (Hypnales) and Sphagnum clades. 16S rRNA gene sequence alignments placed the moss-associated Nostoc and Nostoc-related organisms throughout our Nostocaceae phylogeny, with no obvious single symbiotic clade. We note the presence of multiple alternate nifH genes within the genomes of our cultured Nostoc and Nostoc-related organisms, possibly enabling diazotrophy under variable ecological conditions. We also present evidence for possible endophytic colonization by cyanobacteria of stems of mosses.