Abstract
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.
Highlights
Chlorella (Trebouxiophyceae, Chlorophyta), single-celled green algae, is one of the most famous microalgae genus worldwide that grow in marine, freshwater or edaphic habitats
Numerous studies focusing on morphological characters, ultrastructural composition of the cell wall, biochemical and physiological characters and molecular phylogenetic characteristics have been carried out to revise the system of Chlorella [6,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25]
In this study we present a comprehensive DNA barcode analysis of Chlorella-like species from Chlorella, Chloroidium, Actinastrum and Dictyosphaerium, based on four gene loci rbcL, tufA, ITS (ITS1-5.8S-ITS2) and 16S
Summary
Chlorella (Trebouxiophyceae, Chlorophyta), single-celled green algae, is one of the most famous microalgae genus worldwide that grow in marine, freshwater or edaphic habitats. High levels of cryptic diversity found within Chlorella and the polyphyletic characters between Chlorella and Dictyosphaerium results in fundamental taxonomic revision of these organisms, e.g. the description of many new species and genera [20,23,24,25,32,33]. All these studies indicate that the classification of Chlorella is still very confused and it is urgent to revise the genus. To recover the hidden diversity, more molecular markers that have sufficient nucleotide diversity, low saturation and a simple alignment process should be used for taxonomic identification [32]
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