Efficient bioflocculation and biodiesel production of microalgae Asterococcus limneticus on streptomyces two-stage co-cultivation strategy

Abstract

The green algae Asterococcus limneticus WL2 and phytohormone producing Streptomyces rosealbus MTTC 12951 were grown in a co-cultivation process to quantify the production of indole-3-acetic acid (IAA) and its precursors. The increased concentration of exogenous hormonal activity was detected in the co-cultivation due to the symbiotic interaction between Streptomyces and microalgae. In comparison to monocultivation, co-cultivation of microalgae produced 52% and 83% more tryptophan and IAA in the extracellular space, respectively. A significant amount of tryptophan (Trp) released by microalgae stimulates Streptomyces's production of IAA at an increased level. As a result, the productivity of co-cultivated microalgae increased by 24% and 22%, respectively, in terms of biomass and lipid. Within 24 h of resting time, early deceleration phase co-cultivated cells demonstrated significant bioflocculation efficiency (88%). Using the microalgal growth dynamics as a guide, stages I (0–8 days) and II (9–11 days) of the culture period were designed for assessing the biomass and lipid productivity. The two-stage co-cultivation technique generated 1.2 times more lipids than the single-stage co-cultivation approach. The production and harvesting expenses of in vitro-grown microalgal biomass as well as energy yield suggest co-cultivation, and a two-stage co-cultivation strategy has the potential to improve cost efficiency and energy conservation in biodiesel production.