Journal of Plant Sciences 2014; 2(1): 9-13 Published online January 20, 2014 (http://www.sciencepublishinggroup.com/j/jps) doi: 10.11648/j.jps.20140201.13 Medium improvement for higher growth and longer stationary phase of Dunaliella Suong Nguyen 1 , Duc Tran 1, * , Sixto Portilla 2 , Trung Vo 1 1 School of Biotechnology, International University-VNU, Vietnam 2 Center for Environmental Research and Coastal Oceans Monitoring, Molloy College, 100 Hempstead Avenue, Rockville Centre, NY Email address: tnduc@hcmiu.edu.vn (D. Tran) To cite this article: Suong Nguyen, Duc Tran, Sixto Portilla, Trung Vo. Medium Improvement for Higher Growth and Longer Stationary Phase of Dunaliella. Journal of Plant Sciences. Vol. 2, No. 1, 2014, pp. 9-13. doi: 10.11648/j.jps.20140201.13 Abstract: Beta-carotene is a valuable carotenoid in high demand as a natural food coloring agent, provitamin A, additive to cosmetics, and health food. It can be accumulated up to more than 10% of cellular dry weight of Dunaliella salina under carotenogenic conditions such as high irradiance, high temperature, high salt concentration and nutrient deficiency. High beta-carotene productivity in Dunaliella is best achieved in a two-phase culture system through biomass optimization and beta-carotene induction. A low-cost enriched natural seawater medium (MD4) was previously investigated for biomass optimization (Tran et al., 2014); However, the culture declined rapidly after reaching the stationary phase. Thus the present study is to further improve the effectiveness of this enriched natural seawater medium (MD4) for higher growth and longer stationary phase in order to avoid quick crash phase. Algal culture in MD4 medium used as control medium was subjected to 13 different feeding treatments (TM1  TM13) using a matrix of concentrations of various compounds (NPK, KNO 3 , KH 2 PO 4 ). Dunaliella growth was determined based on chlorophyll concentration, cell density. Results revealed the best feeding treatment was TM4 (NPK 0.15g/l) with cell density doubling one week compared with cell density in the control medium, and is recommended for use in the first phase biomass optimization of Dunaliella. Keywords: Algae, Carotene, Chlorophyll, Cultivation, Dunaliella, Medium 1. Introduction Unicellular green algae Dunaliella belong to the Chlorophytes (Oren 2005, Tran et al 2013). The algae was first described by Dunal in the 1830s (Dunal 1838), but it was not until 1905 that the name Dunaliella was given by Teodoresco (Teodoresco 1905). There are currently 23 recognized Dunaliella species (Pick 1992, Oren 2005). Dunaliella salina TEODORESCO is the type species of the genus, whose vegetative cells are capable of turning red from carotenoid production under environmental stress such as high irradiance, high salinity, or low nutrient concentrations (Lamers et al. 2010, Tran et al. 2014). Dunaliella can be found on all continents and in oceans, salterns and most hyper saline lakes all over the world. Temperature, salinity and nutrients are limiting factors on the growth and development of Dunaliella (Polle et al. 2009, Tran et al 2013). Dunaliella were found in the Great Salt Lake (Post 1977), the Dead Sea (Oren 2005), and from Antarctic salt lakes to salt lakes in Africa, America, Asia, Australia, and Europe (Ginzburg 1987, Borowitzka & Borowitzka 1988, Tran et al 2013). Vietnam has a long coastal seawater resource of 3600km (Tran et al. 2005) with the existence of different strains of Dunaliella salina (Tran et al., 2013) which is a great potential for beta- carotene production. Commercial exploitation in this respect would contribute to regional economic and environmental stability. Various artificial and natural seawater media have been devised for Dunaliella cultivation (Ben-Amotz 1995, Dipak and Lee 2005, García-González et. al 2003, Fazeli et al. 2006, Ana Prieto et al. 2011). Recently a new low cost enriched natural sea water medium (MD4) was investigated for biomass optimization of Dunaliella (Tran et al. 2014). However, there was a premature onset of stationary phase which prompted further efforts to improve the medium to sustain growth. In this study, cultures grown in MD4 medium (as control) were subjected to 13 different feeding treatments (TM1  TM13) before entering the stationary phase using a matrix of concentrations of various mineral salts. Results revealed the best feeding treatment, TM4 (NPK 0.15g/l), doubled cell density one week compared