Identification of NaHCO3 Stress Responsive Proteins in Dunaliella salina HTBS using iTRAQ-based Analysis

Microalgae are a large and diverse group of photosynthetic organisms which can use of solar energy to fixed inorganic carbon (Ci) with efficiency (2-10%) that are ten times greater than higher plants (<1%) due to their high growth rate (1to 3-fold increases in biomass per day) [1,2]. Although CO2 is the predominant carbon source for microalgal cultivation, the low level of dissolution of CO2 in water often leads to escape of large amounts of CO2 from the medium during algae culture. To address this limitation, converting CO2 to bicarbonate in alkali solution for high efficiency of absorption and storage of inorganic carbon (Ci) for microalgae culture is desirable [3]. HCO3 is also more advantageous to maintain the pH range of the culture medium from 6.4 to 10.3, whereas CO2 tends to lower pH below 6.4 [4]. Furthermore, using bicarbonate would also provide a superior alternative for delivering CO2 to an algae culture system [5]. The effects of various HCO3 concentrations (0.5, 1 or 2 g/L) on cell growth and biochemical composition have been well studied. Results on Tetraselmis suecica, Nannochloropsis salina and Scenedesmus sp. CCNM 1077 demonstrated that the cell density, lipid and pigments contents were significantly improved with bicarbonate addition [6,7]. However, reports on responsive proteins to high HCO3 concentrations are very limited. Many fundamental biological questions related to biosynthesis under high HCO3 conditions and regulation of HCO3 tolerance need to be answered to understand how algae balance cation-anion and cope with the osmotic stress in the cell. Answering these questions also allows developing strategies to achieve high carbon utilization rate. However, the characteristics, diversities and evolutions of these high HCO3 tolerance microalgae genes and proteome related to Ci fixation are still not clear.