Fungal communities in Scandinavian lakes along a longitudinal gradient

- Aquatic fungal diversity in the epilimnion of lowland boreal lakes is reported.
- Surface waters of oligotrophic lakes harbour many fungal taxa.
- Both resident and transient components of aquatic fungal communities were detected.
- The most abundant aquatic fungi were taxonomically assigned to Chytridiomycota.
- Longitude and local environment were important in structuring the fungal community.

This study investigates the diversity and distribution of fungal communities in 77 oligotrophic lakes in southern Norway and Sweden using 454-sequencing with fungal-specific primers targeting ITS2 region of the rRNA gene. A total of 232 operational taxonomic units (OTUs) belonging to four recognized phyla were detected. A large proportion (70.69%) of the detected OTUs were Dikarya (Ascomycota and Basidiomycota), while Chytridiomycota dominated quantitatively (63.37% reads). The most abundant aquatic fungi were taxonomically assigned to Chytridiomycota, whose members are known to be saprobes on a large variety of substrates and parasites of phytoplankton, zooplankton, fungi and invertebrates, suggesting that resident fungi strictly depend on surfaces and, therefore, are closely associated with other types of aquatic organisms. Our results indicate that surface waters of oligotrophic lakes harbour a diverse pool of fungi, both with tentative terrestrial and true aquatic origin. Longitude and environmental factors were important in structuring the fungal community composition.