Effects of Carbon Source on Growth Characteristics and Lipid Accumulation by Microalga <i>Dictyosphaerium</i> sp. with Potential for Biodiesel Production

Sustainability and eco-friendliness have both engendered research on alternative replacement of fossil fuel. This study was aimed at determining the effects of varying levels of glucose (10 ~ 40 g/L), and glycerol (0.25 ~ 1.0 mL/L) on the heterotrophic and mixotrophic growth and lipid production by Dictyosphaerium sp. The microalga was cultivated in 2000 mL amber-coloured bottles each containing 1000 mL of a sterile modified BG-11 medium at pH of 7.3. Each bottle was inoculated with a one-week-old pure culture of the isolate (inoculum ratio = 15%) and incubated in the dark at room temperature (30°C ± 2°C) for 10 d. Dictyosphaerium sp. showed the ability to grow heterotrophically and mixotrophically on glucose and on glycerol as a sole carbon substrates. Biomass productivity and specific growth rates did not vary when the initial medium glucose was varied. Lipid accumulation was not dependent on the initial medium glycerol contents. The mean lipid content and productivity of the organism in the present study were high enough to be utilised for industrial processes. Growth and lipid accumulations were better in mixotrophic cultures than both heterotrophic and autotrophic. However, both were better than autotrophic. The percentage compositions of the major fatty acids from Dictyosphaerium sp. grown under different culture conditions show at least five components each. The carbon skeletons eluted ranged from C14 to C22. Oleic acid was a major component of all the fatty acids, which confirm the suitability of the use of the oil for biodiesel production.