Deoxyribonucleic acid reassociation in the taxonomy of the genus Chlorella: V. Chlorella vulgaris, C. luteoviridis, C. minutissima, and C. zofingiensis

Combining and Comparing Coalescent, Distance and Character-Based Approaches for Barcoding Microalgaes: A Test with Chlorella-Like Species (Chlorophyta)

Several different barcoding methods of distinguishing species have been advanced, but which method is the best is still controversial. Chlorella is becoming particularly promising in the development of second-generation biofuels. However, the taxonomy of Chlorella-like organisms is easily confused. Here we report a comprehensive barcoding analysis of Chlorella-like species from Chlorella, Chloroidium, Dictyosphaerium and Actinastrum based on rbcL, ITS, tufA and 16S sequences to test the efficiency of traditional barcoding, GMYC, ABGD, PTP, P ID and character-based barcoding methods. First of all, the barcoding results gave new insights into the taxonomic assessment of Chlorella-like organisms studied, including the clear species discrimination and resolution of potentially cryptic species complexes in C. sorokiniana, D. ehrenbergianum and C. Vulgaris. The tufA proved to be the most efficient barcoding locus, which thus could be as potential "specific barcode" for Chlorella-like species. The 16S failed in discriminating most closely related species. The resolution of GMYC, PTP, P ID, ABGD and character-based barcoding methods were variable among rbcL, ITS and tufA genes. The best resolution for species differentiation appeared in tufA analysis where GMYC, PTP, ABGD and character-based approaches produced consistent groups while the PTP method over-split the taxa. The character analysis of rbcL, ITS and tufA sequences could clearly distinguish all taxonomic groups respectively, including the potentially cryptic lineages, with many character attributes. Thus, the character-based barcoding provides an attractive complement to coalescent and distance-based barcoding. Our study represents the test that proves the efficiency of multiple DNA barcoding in species discrimination of microalgaes.

Phylogenetic position of some Chlorella species within the chlorococcales based upon complete small-subunit ribosomal RNA sequences

Complete small-subunit rRNA (16S-like rRNA) coding region sequences were determined for eight species of the Chlorococcales (Chlorophyceae). The genera investigated include Prototheca, Ankistrodesmus, Scenedesmus, and five Chlorella species. Distance matrix methods were used to infer a phylogenetic tree that describes evolutionary relationships between several plant and green algal groups. The tree exhibits a bifurcation within the Chlorococcales consistent with the division into Oocystaceae and Scenedesmaceae, but three of the five Chlorella species are more similar to other algae than to Chlorella vulgaris. All of the sequences contain primary and secondary structural features that are characteristic of 16S-like rRNAs of chlorophytes and higher plants. Anikstrodesmus stipitatus, however, contains a 394-bp group I intervening sequence in its 16S-like rRNA coding region.