A comprehensive study of Macrochaete oelandica sp. nov., the second known cyanobiont of lichen Placynthium nigrum in Europe

Cyanobacteria, a diverse group of photosynthetic bacteria, act as primary symbionts for carbohydrate production in about 10% of lichenized fungi, referred to as cyanolichens. This study investigates the effect of different living conditions on the morphology of one cyanobacterium, comparing the cyanobacterium in the lichen symbiosis with the same species in culture. The lichen Placynthium nigrum served as a suitable model. We examined the cyanobacterial 16S rRNA, fungal mtSSU rDNA, and MCM7 sequences using ML analyses, along with analysis of 16S-23S ITS sequences to explore DNA helix structures. Based on the results, we propose here a new cyanobacterial species, Macrochaete oelandica. The morphological analyses revealed that a genetically identical cyanobacterium obtained from the same lichen thallus exhibits different morphological characteristics depending on their living conditions: incompletely developed features due to the limitations when living in symbiosis within the lichen thallus versus fully developed morphological features when cultured.