Characterization of a new Dunaliella salina strain MSI-1 based on nuclear rDNA ITS sequences and its physiological response to changes in composition of growth media

Since the first formal description of the unicellular green algae Dunaliella salina, its presence in hypersaline environments worldwide and its physiological responses to different environmental conditions have been studied extensively. Moreover, due to massive carotenoid accumulation by some strains under specific growth conditions, its biotechnological applications have attracted a great deal of scientific interest. In this study, the phylogenetic relationship, growth, and carotenogenesis of a new strain of Dunaliella salina isolated from Maharlu salt lake in Shiraz (latitude 29.26°N, longitude 52.48°E), Iran were investigated. First, a phylogram based on neighbor-joining analysis of the nuclear rDNA ITS (ITS-1 + 5.8 rDNA + ITS-2) sequence data was constructed. The phylogenetic tree showed that the new isolate is part of a major clade containing several strains of D. salina and was designated as D. salina MSI-1. Then, the responses of the new isolate to the initial pH of the culture media and different concentrations of nitrate, NH₄ ⁺, and citrate were examined. As with other strains of D. salina, growth and carotenogenesis were controlled by the levels of nitrate and NH₄ ⁺ in the growth media. Low available nitrogen negatively affected growth but enhanced carotenoid accumulation. Insensitivity of carotenogenesis to citrate indicates a minor contribution of cytosolic IPP synthesis to the overall carotenoid production. Despite changes in the initial pH of the culture media over the experimental period, the initial pH had marked effects on the growth and carotenogenesis of the new isolate. These effects, together with the higher cell carotenoid content observed at pH 11.0, await further research. The results confirm that the analysis of the ITS sequences is a reliable basis for determination of the genetic relatedness among strains of the genus Dunaliella, and the search for strains with novel characteristics may have valuable biotechnological applications.