Phenotypic and genetic characterization of Dunaliella (Chlorophyta) from Indian salinas and their diversity

BACKGROUND The genus Dunaliella (Class - Chlorophyceae) is widely studied for its tolerance to extreme habitat conditions, physiological aspects and many biotechnological applications, such as a source of carotenoids and many other bioactive compounds. Biochemical and molecular characterization is very much essential to fully explore the properties and possibilities of the new isolates of Dunaliella. In India, hyper saline lakes and salt pans were reported to bloom with Dunaliella spp. However, except for the economically important D. salina, other species are rarely characterized taxonomically from India. Present study was conducted to describe Dunaliella strains from Indian salinas using a combined morphological, physiological and molecular approach with an aim to have a better understanding on the taxonomy and diversity of this genus from India. RESULTS Comparative phenotypic and genetic studies revealed high level of diversity within the Indian Dunaliella isolates. Species level identification using morphological characteristics clearly delineated two strains of D. salina with considerable β-carotene content (>20 pg/cell). The variation in 18S rRNA gene size, amplified with MA1-MA2 primers, ranged between ~1800 and ~2650 base pairs, and together with the phylogeny based on ITS gene sequence provided a pattern, forming five different groups within Indian Dunaliella isolates. Superficial congruency was observed between ITS and rbcL gene phylogenetic trees with consistent formation of major clades separating Indian isolates into two distinct clusters, one with D. salina and allied strains, and another one with D. viridis and allied strains. Further in both the trees, few isolates showed high level of genetic divergence than reported previously for Dunaliella spp. This indicates the scope of more numbers of clearly defined/unidentified species/sub-species within Indian Dunaliella isolates. CONCLUSION Present work illustrates Indian Dunaliella strains phenotypically and genetically, and confirms the presence of not less than five different species (or sub-species) in Indian saline waters, including D. salina and D. viridis. The study emphasizes the need for a combined morphological, physiological and molecular approach in the taxonomic studies of Dunaliella.