Chytrid Fungi Associated with Pollen Decomposition in Crater Lake, Oregon

Abstract

We identified chytrid fungi that were attached to pine pollen on the surface of Crater Lake. Fungi were identified by large subunit (LSU) rRNA gene sequencing of lake pollen extracts and by isolation of a chytrid fungus that was present on the pollen. LSU rRNA PCR products were cloned, sequenced and identified. The majority of eukaryotic LSU rRNA sequences associated with pollen were found to be members of the chytrid order Rhizophyidiales. A fungal isolate was characterized culturally, morphologically, and by DNA sequencing and was identified as a member of the genus Paranamyces, in the order Rhizophydiales. In addition, protist LSU rRNA sequences from the phylum Ciliophora were found. The concentrations of dissolved organic matter, nitrogen, and phosphate in surface water that had visible pollen rafts increased according to the concentration of pollen in the water. Each of these nutrients was detected at several fold higher levels in water with pollen rafts as compared to surface water lacking pollen rafts. These results provide evidence for the role of chytrid fungi in nutrient release from pollen deposited on Crater Lake.