Taxonomic reassessment of the genus Chlorella (Trebouxiophyceae) using molecular signatures (barcodes), including description of seven new species.

Abstract

Abstract:After the description of Chlorella vulgaris by Beijerinck, 120 years ago, members of the genus Chlorella belong to the best studied green algae worldwide. However, numerous open questions remained regarding their systematics. Recent molecular studies showed the polyphyly of the genus within the Chlorophyceae and Trebouxiophyceae. Chlorella-species were traditionally characterized by spherical to oval cell shape, solitary lifeform and the absence of mucilaginous envelopes. The challenge in the past was how to distinguish species due to their high phylogenetic diversity combined with a limited amount of morphological characters. Using a polyphasic approach of SSU-and ITS rDNA phylogeny, secondary structure of the ITS and light microscopic observations, we were able to detect six lineages with Dictyosphaerium-like strains in close relationship to C. vulgaris, here described or combined newly as C. coloniales sp. nov., C. pituita sp. nov., C. pulchelloides sp. nov., C. singularis sp. nov., C. elongata comb. nov. and C. chlorelloides comb. nov. Furthermore, three new species without mucilage were described as C. lewinii sp. nov., C. rotunda sp. nov. and C. volutis sp. nov. Using the 5.8S rRNA and part of the ITS-2 as molecular signature (barcode), we were able to distinguish not only the five already known species of Chlorella, C. vulgaris, C. sorokiniana, C. heliozoae, C. lobophora and C. variabilis but the seven new species and two new combinations as well. CBCs and hemi-CBCs within the secondary structure of the ITS-2 confirmed the separation of the species. Our study led to a new understanding of the evolution of morphology within the genus Chlorella and to an emendation of the generic description.

Generic and species concepts inMicroglena(previously theChlamydomonas monadinagroup) revised using an integrative approach

“…However, the relationship among these lineages is unresolved by the concatenated SSU and ITS data (no Bayesian and bootstrap support). Therefore, to decide if the 13 lineages represent different species, the conserved region of the ITS-2 secondary structure was analysed using the CBC approach proposed by Coleman (2000Coleman ( , 2009, Moniz & Kaczmarska (2009) and Bock et al (2011). Figures 3 and 4 and Table 1 show that all 13 lineages differ by at least one CBC, mostly by more (up to 18).…”

Genotypic diversity of Dictyosphaerium-morphospecies (Chlorellaceae, Trebouxiophyceae) in African inland waters, including the description of four new genera.

“…The liquid was discarded and DNA pellet was washed with ethanol (80%). The SSU and ITS rRNA genes were amplified and sequenced as described by BocK et al (2011a).…”

“…Furthermore, investigations on living and cultured algal material including sequence analyses are largely missing. Until now, only few cultured strains of coccoid green algae from tropical Africa have been investigated by modern systematic approaches (luo et al 2006BocK et al 2010BocK et al , 2011aKrienitz et al 2010.…”

Phylogenetic position of Ecballocystis and Ecballocystopsis (Chlorophyta).

“…Recently, the conventional concept of some chlorellacean genera were evaluated and phylogenetic works revealed relatively long distances between them and the "classical" oocystacean genera. The genus Chlorella, newly found to include taxa with a mucilaginous envelope and colonial lifeform was a member of Chlorellaceae (Luo et al 2010;BoCK et al 2011). Tetraedron was placed on the monophyletic lineage of Hydrodictyaceae (BuChheim et al 2005).…”