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Algae from Extremophilic Conditions and Their Potential Applications
Published in Shashi Kant Bhatia, Sanjeet Mehariya, Obulisamy Parthiba Karthikeyan, Algal Biorefineries and the Circular Bioeconomy, 2022
Ashiwin Vadiveloo, Tasneema Ishika, David Chuka-Ogwude, Mohammadjavad Raeisossadati, Ângelo P. Matos
Carotenoids represent the most common and diverse secondary pigments available in nature (Henríquez et al., 2016). In microalgae, including the halophilic Dunaliella salina, the phytoene synthase (PSY) catalyses represent the key precursor regulatory step for the synthesis of carotenoids. Through past studies, the PSY gene isolated from Dunaliella salina has been successfully inserted and expressed in C. reinhardtii through nuclear transformation, creating a stable corresponding PSY transcript level that enhanced the synthesis of violaxanthin, lutein, and β-carotene (Couso et al., 2011). Genomics of the poly-extremophilic red microalga Galdieria sulphuraria that have a unique position within extremophile microalgae, due to its resistance to acid (pH 0.0), high temperature (56°C), high salinity (1.5 M NaCl), heavy metals, and various other abiotic stressors was investigated (Barbier et al., 2005). For instance, the mitochondrial and plastid genomes of G. sulphuraria were compared to genomic analysis with other red microalgae (Jain et al., 2015). Their results indicated that unfavourable environmental conditions, in which Galdieria lives, place additional mutational pressures on the mitogenome for energy production, while the decrease dependence on photosynthesis, and the availability of multiple intergenic stem-loop structures is believed to play a critical role to prevent the unwinding of DNA in extreme conditions. Additional examples of genetic engineering and genome studies of extremophile microalgae are highlighted in Table 9.6.
Fucoxanthin
Published in M. Jerold, V. Sivasubramanian, Biochemical and Environmental Bioprocessing, 2019
Lohr and Wilhelm (1999) found out that violaxanthin as the major precursor for the synthesis of almost all carotenoids. Fucoxanthin in the diatom Phaeodactylum tricornutum was synthesized from violaxanthin through diadinoxanthin. Lichtenthaler (1999) proved that isopentenyl pyrophosphate (IPP) was synthesized in 1-deoxy-D-xylulose-5-phosphate (DOXP) pathway from pyruvate and glyceraldehyde. Phytoene synthase converts IPP to phytoene, a C40 compound. Oxygenic phototrops require three enzymes for the conversion of phytoene to lycopene. They are phytoene desaturase, δ-carotene desaturase, and cis-carotene isomerase. Bacteria use only phytoene desaturase for the conversion of phytoene to lycopene. Then lycopene is converted to β-carotene by lycopene cyclase (Wang et al., 2014). β-Carotene is hydroxylated by β-carotene hydroxylase to zeaxanthin (Takaichi, 2011).
High yield production of lipid and carotenoids in a newly isolated Rhodotorula mucilaginosa by adapting process optimization approach
Published in Biofuels, 2023
Ravi Gedela, Ashish Prabhu, Venkata Dasu Veeranki, Pakshirajan Kannan
In oleaginous yeast, the hydrophilic substrate is consumed via the de novo pathway, and the lipid accumulation proceeds with the depletion of nitrogen compound, which in turns activate AMP deaminase. This activity leads toa series of cascade reactions, which disturbs the TCA cycle in mitochondria and splits the ATP-citrate lyase and acetyl-CoA and oxaloacetate. Further, the acetyl CoA is carboxylated in to malonyl CoA which is the first step of lipid synthesis, and then followed a by series of enzymatic reactions catalyzed by a complex of fatty acid synthases, which ultimately leads to the synthesis of triacyl glycerol. Further in yeast such as Rhodoturula sp that is capable of synthesizing carotenoids, which initiates by the conversion of acetyl CoA to 3 hydroxyl-3 methylglutaryl-CoA catalyzed by 3 hydroxyl-3 methylglutaryl-CoA synthase. Consequently, the HMG- CoA is reduced to mevalonic acid by HMG-CoA reductase and the cascade of reaction takes place for the production of isopentenyl diphosphate (IPP), which is further subjected to an isomerization reaction to form dimethylallyl pyrophosphate (DMAPP), and the addition of 3 molecules of IPP to DMAPP results in geranylgeranyl pyrophosphate (GGPP). The GGPP undergoes a condensation reaction catalyzed by phytoene synthase to form phytoene and finally converted to β-carotene [18]. The biochemical pathway for the formation of lipids and carotenoids in Rhodotorula sp is depicted in Figure S1 (Supplementary Material).