Enhancing Biomass Productivity and Photosynthetic Pigments Content of an Egyptian Anabaena Ambigua Blue-Green Alga Isolate

Abstract

Maximizing biomass and pigments productivities in microalgae are important objectives to achieve in order for algal culturing to become economically feasible. This study, thus, aims to evaluate the effects of type of culture as well as altering the composition of BG110 medium on enhancing biomass, chlorophyll-a and total carotenoids of an Egyptian Anabaena ambigua blue-green isolate. For this purpose, the isolate was subjected to different nutrient BG110 medium concentration (1X and 4X), different types of culturing (batch and Semi-continuous culture), adding nitrogen source (7 mM NaNO3) or inorganic carbon source (50 mg CaCO3 per liter), as well as subjecting it to moderate salinity stress (50 mM NaCl). Overall, growth curves revealed a significant stimulation of growth under BG110 medium 4X concentration together with NaNO3 and CaCO3 treatments. Results revealed that the best biomass production at 21 days culture age (late exponential phase) was obtained using BG110 medium 4X concentration (ca. 2050 mg L-1) followed by CaCO3 treatment (ca. 1400 mg L-1). Using semi-continuous culture (ca. 1499 mg L-1) also proved to give significantly more biomass when compared to batch culturing method. Also, using 50 mM NaCl did not significantly affect biomass, indicating the possibility of culturing this isolate with brackish or diluted sea water. Similar results were obtained at 28 days culture age (stationary phase). Regarding pigment contents and productivities, the use of 50 mM NaCl significantly increased both chlorophyll-a and total carotenoids at 21 and 28 days culture age. Moreover, NaNO3 and CaCO3 treatments proved to be beneficial to enhance chlorophyll-a and total carotenoids, respectively. Nevertheless, the type of culturing (batch or semi-continuous) seemed to have very little effect on pigments contents and productivities. Future studies involving other media components and their combination will increase our knowledge on the possible physiological treatments to enhance biomass of microalgae in a sustainable way.