Evidence for a mutualistic relationship between the cyanobacteria Nostoc and fungi Aspergilli in different environments

Symbiotic partnerships are widespread in nature and in industrial applications yet there are limited examples of laboratory communities. Therefore, using common photobionts and mycobionts similar to those in natural lichens, we create an artificial lichen-like symbiosis. WhileAspergillus nidulansandAspergillus nigercould not obtain nutrients from the green algae,Chlorella, andScenedesmus, the cyanobacteriaNostocsp. PCC 6720 was able to support fungal growth and also elevated the accumulation of total biomass. TheNostoc-Aspergillusco-cultures grew on light and CO(2)in an inorganic BG11 liquid medium without any external organic carbon and fungal mycelia were observed to peripherally contact with theNostoccells in liquid and on solid media at lower cell densities. Overall biomass levels were reduced after implementing physical barriers to indicate that physical contact between cyanobacteria and heterotrophic microbes may promote symbiotic growth. The syntheticNostoc-Aspergillus nidulansco-cultures also exhibited robust growth and stability when cultivated in wastewater over days to weeks in a semi-continuous manner when compared with axenic cultivation of either species. TheseNostoc-Aspergillusconsortia reveal species-dependent and mutually beneficial design principles that can yield stable lichen-like co-cultures and provide insights into microbial communities that can facilitate sustainability studies and broader applications in the future.