Augmentation of the Photoreactivation Gene in Fremyella diplosiphon Confers UV-B Tolerance

Abstract

In spite of the enormous potential of cyanobacteria as a renewable energy source, elevated UV exposure is a major impediment to their commercial viability and productivity. Fremyella diplosiphon is a widely explored cyanobacterium with great biofuel capacity due to its high lipid content. To enhance UV stress tolerance in this species, we overexpressed the photoreactivation gene ( phr A ) that encodes for photolyase DNA repair enzyme in the wild type F. diplosiphon (B481-WT) by genetic transformation. Our efforts resulted in a transformant (B481-ViAnSa) with a 3808-fold increase in the phr A mRNA transcript level and enhanced growth under UV-B stress. Additionally, DNA strand breaks in the transformant were significantly lower after 12 and 16 h of UV radiation, with significantly higher dsDNA recovery in B481-ViAnSa (98.1%) compared to that in B481-WT (81.5%) at 48 h post irradiation. Photosystem II recovery time in the transformant was significantly reduced (48 h) compared to that in the wild type (72 h). Evaluation of high-value fatty acid methyl esters (FAMEs) revealed methyl palmitate, the methyl ester of hexadecenoic acid (C16:0), to be the most dominant component, accounting for 53.43% of the identified FAMEs in the transformant. Results of the study offer a promising approach to enhance UV tolerance in cyanobacteria, thus paving the way to large-scale open or closed pond cultivation for commercial biofuel production.

Impact of Ascorbic Acid on Zero-Valent Iron Nanoparticle and UV-B Mediated Stress in the Cyanobacterium, Fremyella diplosiphon

“…As a micronutrient, iron is essential for the metabolism and growth of cyanobacteria and functions as a cofactor in enhancing nitrogenase activity, a crucial enzyme responsible for nitrogen fixation in cyanobacteria [ 20 ]. In addition to nanomaterials, optimal UV-B radiation is essential for energy-dependent processes such as photosynthesis, growth, survival, cell differentiation, genome integrity, and total lipid profiles [ 3 , 21 ]. Nevertheless, cyanobacteria are challenged by toxic ROS due to drastic changes in metal availabilities and intense UV-B illumination, when the amount of electrons they produce exceeds the amount they need to assimilate inorganic nutrients.…”

“…Additionally, cyanobacteria have attracted considerable attention as a sustainable source of energy due to their metabolic versatility. Several strategies such as genetic transformation to overexpress target genes in cyanobacteria have been pursued to enhance their biofuel production efficacy [ 3 ].…”

Lipid production and cellular changes in Fremyella diplosiphon exposed to nanoscale zerovalent iron nanoparticles and ampicillin

“…Fremyella diplosiphon B481-SD strain, overexpressed with the sterol desaturase gene (accession MH329183), was used in this study. Active cultures were grown in Blue-Green-11 (BG-11) medium and 4,2-Hydroxyethyl, 1-piperazineethanesulfonic acid (HEPES) under wide-spectrum red light (650 nm) and shaking continuously at 170 rpm at 28 °C in an Innova 44R shaker (Eppendorf, Hamburg, Germany) [ 16 ]. The light fluence rate was adjusted to 30 µmol/m 2 /s using the model LI-190SA quantum sensor (Li-Cor, USA).…”