A New Deep-Water Epilithic Green Alga, Ulvella lacustris, from an Alpine Brackish Lake in Qinghai–Tibet Plateau

Abstract

Ulvella species are widely distributed in ocean and freshwater habitats and from high latitudes to the tropics. However, no species of this genus have been found in the Qinghai–Tibetan Plateau. In the present study, five rock specimens were collected from the bottom of Qinghai Lake at a depth of about 15–28 m, from which three unialgal strains were isolated. These strains were characterized by prostrate pseudoparenchyma, irregular or radial branch filaments, and mono- or polystromatic discs or rosettes formed by consecutive filaments, with thalli that can grow up to 180 um in length, suggesting that they may be Ulvella species. Phylogenetic analysis based on 18S rDNA and tufA cpDNA sequences revealed that the isolates formed a strong branch among other Ulvella species and were closely related to Ulvella leptochaete and Ulvellawaernii. This result was also confirmed by neighbor-joining tree inference based on ITS2 secondary structure. Unlike other members of Ulvella, the isolated strain was characterized by its unique habitat, field morphology of thallus, size of vegetative cells, and number of pyrenoids. Based on these morphological differences, the phylogenetic analysis, and the comparison of ITS2 secondary structure with relative species, the strain isolated in this study was proposed to be a novel Ulvella sp. The alga was found on the bottom of brackish lakes on the Qinghai–Tibetan Plateau, which meant that our sampling range needed to be expanded further.