Identification of Chlorella Spp. Isolates Using Ribosomal DNA Sequences

Abstract

Members of the Chlorella species are very simple unicellular algae, easy to cultivate and widely used in various physiological studies. Their morphological and physiological characteristics, however, normally change with the environment, making species identification difficult. To elucidate the relationship between various strains of Chlorella, this investigation analyzed the nuclear-encoded and chloroplast-encoded small-subunit rDNA sequences of four strains of Chlorella using PCR techniques. These strains were isolated from different rivers and ponds in Taiwan and Indonesia, and then compared and identified using stock strains of Chlorella spp. from the culture collection centers, and published DNA sequence data from Genbank. Experimental results attributed the isolated strains mainly to C. sorokiniana, a common species of green algae which grows in freshwater ecosystems at around 36°C. In addition, phylogenetic analysis of nuclear-encoded and chloroplast-encoded small-subunit rDNA sequences from spherical green algae of the genera Chlorella revealed the sequences to closely resemble each other. Further analyses indicated that Chlorella spp. 216 was close to Chlorella spp. 21 and I. Generally, the chloroplast data sets supported the lineages more than the nuclear data sets did. Strains 21 and 216 were closer to I. Comparisons with some of the morphological and biochemical data indicated that the phylogenetic analysis of rDNA sequences was in line with results obtained by conventional methods.