IAA induced biomass and lipid overproduction in microalga via two-stage cultivation strategy: Characterization using FTIR/CHNS/TGA/DTG and 1H- NMR for bioenergy potential

Abstract

Microalgae are an excellent carbon concentrators with substantial lipid content. However, biomass production vis-à-vis lipid hyperaccumulation is a major constraint in the biofuel economy. In this regard, Dunaliella salina, an oleaginous, wall less microalga, was grown in graded concentration of indole-3-acetic acid (IAA). There was a significant increase in biomass (1.57-fold), photosynthetic efficiency (Fv/Fm = 0.72), and chlorophyll a content in 0.25 mg/L IAA supplemented cultures over the control (stage I). However, supplementation of IAA under nitrogen deprivation (stage II) led to a significant rise in the lipid content (47 % DCW), carbohydrate (18.37 %) and simultaneous reduction in the oxidative status (MDA, H2O2, O2·−, OH·) over the control. Further, 0.25 mg/L IAA supplemented cultures under nitrogen starvation were undertaken for biomass and lipid characterization. Nile red based flow cytometric analysis revealed an apparent increase in the neutral lipid fluorescence, also validated by 1H- NMR based lipidome, revealing the presence of triacylglycerol (TAG, 4.12–4.31 ppm). FTIR spectra revealed the increased absorbance at 2926 cm−1, 1740 cm−1 and 1025 cm−1, validating the increased carbohydrate and lipid, while biomass pyrolysis showed 81.42 % decomposition in the active pyrolytic zone as recorded by the TGA/DTG analysis. Interestingly, elemental analysis (CHNS) of the biomass showed an increased carbon and hydrogen %, HHV (19.94 MJ kg−1), H/C ratio (1.78), and CO2 fixation rate. Thus, the present study opens new avenues for the economic feasibility of bioenergy/biofuel production from microalgal biomass at commercial scale. © 2024 Elsevier Ltd