Comparative studies on biomass productivity and lipid content of a novel blue-green algae during autotrophic and heterotrophic growth.

Abstract

Algae have long been acclaimed as the attractive renewable source for generating third-generation biofuels, particularly biodiesel. Under the present investigation, the trends of production of biomass and lipid during the autotrophic and heterotrophic growth of newly isolated blue-green algae, Leptolyngbya subtilis JUCHE1, were compared and correlated with the variation in C-sources. In the autotrophic and heterotrophic growth studies, CO2 and glycerol were respectively used as the inorganic and organic C-sources maintaining equivalence in the initial amount of carbon. Light was used as the source of energy in both cases. The concentration of CO2 in the feed gas stream was varied from 5 to 20% (% v/v). Equivalent quantity of carbon was supplied through glycerol during heterotrophic growth. Small-scale closed algal bioreactors were used for growing the algae at 37 °C and 2.5 kLux light illumination in batch mode for 0-4 days. Primarily, higher biomass production from glycerol compared with CO2 was observed. In case of photoautotrophic growth, the maximum values of biomass and lipid productivity, obtained at 15% CO2, were 0.1857 g/L/d and of 0.020 g/L/d respectively. The maximum biomass productivity of 0.2733 g/L/d was obtained for photoheterotrophic growth at a glycerol concentration equivalent to 15% CO2 (v/v). Under photoheterotrophic growth of Leptolyngbya subtilis JUCHE1, lipid productivity of 0.0702 g/L/d was obtained at glycerol concentration equivalent to 5% (v/v) CO2, which is 4.66-fold higher than that obtained under corresponding photoautotrophic condition. The "switch-over" from the autotrophy to the photoheterotrophy instigated the oleaginous anabolism and consequent lipid enrichment in L. subtilis JUCHE1, which can be extracted and converted to biodiesel.