Molecular identification of Dunaliella viridis Teod. strain MSV-1 utilizing rDNA ITS sequences and its growth responses to salinity and copper toxicity

In addition to biochemical, physiological and morphological analysis, molecular studies provide additional information for establishing phylogenetic relationships among different species and strains of the genus Dunaliella. In the present study, based on neighbor- joining analysis of the nuclear rDNA ITS sequence, a novel strain of the green algae Dunaliella viridis was identified from Maharlu salt lake in Shiraz, Iran. The phylogenetic tree shows that the new strain is part of a clade containing several strains of D. viridis. The new strain was designated Dunaliella viridis MSV-1 and submitted to the GenBank under the accession number HQ864830.  The optimum salinity for MSV-1 growth is between 1.0 to 1.5 M NaCl and does not turn red up to 4.5 M NaCl, confirming identity of the isolated strain. With respect to growth response to copper toxicity, increase in Cu2+ concentration from 1 to 30 µM, caused progressive increase in cell number ml-1 of culture over time, whereas reduction in cell number occurred at 100 and 200 µM Cu+2. Nano copper (colloidal copper with 40 nm dimensions) showed less toxicity compared to the ionic form. Cell number ml-1 of culture did not change up to 200 µM nano copper but decreased at 500 µM. In conclusion, the analysis of the ITS sequence is a reliable basis for establishing evolutionary relationships among species and strains of the genus Dunaliella and due to rapid growth at 1.5 M NaCl and high cell density, D. viridis MSV-1 is a good candidate for biofuel production from microalgae.