Autumnella lusatica gen. nov. and sp. nov. (Chlorophyta, Trebouxiophyceae), a new phytoplankton species in acidic lignite pit lakes

We describe a novel green algal species that has been recorded for a decade but not specified during phytoplankton monitoring of acidic pit lakes in Saxony, Germany. Based on sequences of 18S rDNA, the ITS1-5.8S rDNA-ITS2 region and 16S rDNA, the novel alga is described as Autumnella lusatica gen. nov. & sp. nov. within the class Trebouxiophyceae. A close phylogenetic relationship led to the assignment of the morphologically similar Koliella corcontica Hindak to the new genus. Autumnella lusatica grows well in a neutral culture medium for green algae. In the type locality, the new species is characterized by (1) tolerance against acidity down to pH 3.0; (2) ability to propagate and establish enormous biovolumes at conditions of acidic pH, low total phosphorus (TP) and total inorganic carbon (TIC) concentrations; and (3) unusual seasonal growth dynamics with maximum and minimum biovolumes in October and June, respectively. As in other lakes, A. lusatica was abundant in the oligotrophic lake, Haberdorfer See, and caused chlorophyll a concentrations up to 30 mu g l(-1) at pH values between 3.0 and 3.5, TIC concentrations of usually < 1 mg l(-1) and TP of < 10 mu g l(-1) in the euphotic zone. During its main growth phase, A. lusatica increased the total carbon in the euphotic zone on average by 2 mg l(-1) or a factor of eight by C accumulation. Its growth rate could be even greater than that of some typical mixotrophic competitors. During lake stratification, the species preferred the epilimnion, supported by the formation of oil droplets in the cytoplasm.