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We provide physiological and metabolic insights into the complex role of γ-aminobutyric acid (GABA) in fine-tuning algal metabolism to improve productivity. Genetic engineering strategies to improve algal GABA biosynthesis are also discussed. Our aim is to provide an understanding of how GABA can be used for cost-competitive algae-based biofuels and bioproducts.

Pyrene (polycyclic aromatic hydrocarbon), an anthropogenic organic pollutant prevalent in various ecological units, receives more attention for bioremediation and energy transformation using microalgae. In this study, we have used pyrene pollutant (50–500 ppm) to evaluate the half-maximal inhibitory concentrations (IC50) of Chlorella sorokiniana and the impact on metabolites as well as the induction of lipid biosynthesis to produce renewable biodiesel. Pyrene concentration at 230 ppm (IC50) caused half-maximum inhibition for the 96 h incubation. The harvest in the stationary stage (day 16) for C. sorokiniana revealed a biomass generation of 449 ± 7 mg L−1 and 444 ± 8 mg L−1 dcw in the control medium and pyrene IC50 medium, respectively. An insignificant decline in biomass generation (1.2%) was observed due to the stress effect of the pyrene IC50 medium on metabolic biosynthesis. Although contrary to biomass generation, IC50 of pyrene assisted to induce lipid biosynthesis in C. sorokiniana. The improvement in lipid biosynthesis was observed as ~24% higher in pyrene IC50 compared to the control medium. The chemical composition of the microalgae biomass, metabolites, and lipids was examined using FTIR spectra. The extracted lipid was transesterified to produce biodiesel via methanolic-H2SO4 catalysis. The renewable biodiesel obtained was evaluated using FTIR and 1H NMR spectra. The transformation efficiency of the lipid of C. sorokiniana in biodiesel was calculated as ~81%. This research offers the incentive in lipid biosynthesis in microalgae cells using pyrene for the production of renewable and sustainable ecological biofuels along with bioremediation of pyrene.

Microalgae have been the subject of recent research as a sustainable feedstock for the large-scale production of metabolites for commercial purposes. This study presents a green bio-remediation approach towards heavy metal contaminations and biomass production for biofuels in microalgae metabolomics and lipidomics approaches. Two novel microalgae, Chlorosarcinopsis bastropiensis and Polyedriopsis spinulosa, were isolated during the study and subjected to Pb(II) and Cd(II) pollutants. The isolated microalgae strains have shown a varied behavior towards cell growth, pigment accumulation, and lipids profiles during the impact of short-term (96 h) and long-term (14 d) heavy metal tolerance. Cell viability and IC50 value (397.75 mg/L for C. bastropiensis and 490.16 mg/L for P. spinulosa) have indicated higher tolerance towards Pb(II) in both microalgae. FTIR analysis of microalgal biomass has revealed insignificant differences during long and short-term heavy metal toxicity, clearly indicating the bio-tolerance for Pb(II) and Cd(II) in both microalgae. Principal component analysis has revealed the expression of metabolites (such as glycine, proline, valine, isoleucine, linoleic acid, glucose, sucrose, etc.) under heavy metal stress. 1H NMR analysis has demonstrated the prominent expression of metabolites under heavy metal stress. ICP-MS-based studies do not reflect the correlation between cellular tolerance and bioaccumulation of each heavy metal by both microalgae. Lipidomics based on 1H NMR has revealed an increase in unsaturated fatty acids under the impact of heavy metals. Therefore, this study offers a sustainable bioremediation technique for heavy metal contaminants and biomass production with significant enhancement of metabolites and lipid components for biofuels and/-or other commercial applications.