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  1. Fremyella diplosiphon is an ideal third-generation biofuel source due to its ability to produce transesterified lipids. While nanofer 25s zero-valent iron nanoparticles (nZVIs) improve lipid production, an imbalance between reactive oxygen species (ROS) and cellular defense can be catastrophic to the organism. In the present study, the effect of ascorbic acid on nZVI and UV-induced stress in F. diplosiphon strain B481-SD was investigated, and lipid profiles in the combination regimen of nZVIs and ascorbic acid compared. Comparison of F. diplosiphon growth in BG11 media amended with 2, 4, 6, 8, and 10 mM ascorbic acid indicated 6 mM to be optimal for the growth of B481-SD. Further, growth in 6 mM ascorbic acid combined with 3.2 mg/L nZVIs was significantly higher when compared to the combination regimen of 12.8 and 51.2 mg/L of nZVIs and 6 mM ascorbic acid. The reversal effect of UV-B radiation for 30 min and 1 h indicated that ascorbic acid restored B481-SD growth. Transesterified lipids characterized by gas chromatography–mass spectrometry indicated C16 hexadecanoate to be the most abundant fatty acid methyl ester in the combination regimen of 6 mM ascorbic acid and 12.8 mg/L nZVI-treated F. diplosiphon. These findings were supported by microscopic observations in which cellular degradation was observed in B481-SD cells treated with 6 mM ascorbic acid and 12.8 mg/L nZVIs. Our results indicate that ascorbic acid counteracts the damaging effect of oxidative stress produced by nZVIs. 
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    Free, publicly-accessible full text available May 1, 2024
  2. The use of renewable energy to reduce fossil fuel consumption is a key strategy to mitigate pollution and climate change, resulting in the growing demand for new sources. Fast-growing proprietary cyanobacterial strains of Fremyella diplosiphon with an average life cycle of 7–10 days, and a proven capacity to generate lipids for biofuel production are currently being studied. In this study, we investigated the growth and photosynthetic pigmentation of a cyanobacterial strain (SF33) in both greenhouse and outdoor bioreactors, and produced biocrude via hydrothermal liquefaction. The cultivation of F. diplosiphon did not significantly differ under suboptimal conditions (p < 0.05), including in outdoor bioreactors with growth differences of less than 0.04 (p = 0.035) among various batches. An analysis of the biocrude’s components revealed the presence of fatty acid biodiesel precursors such as palmitic acid and behenic acid, and alkanes such as hexadecane and heptadecane, used as biofuel additives. In addition, the quantification of value-added photosynthetic pigments revealed chlorophyll a and phycocyanin concentrations of 0.0011 ± 5.83 × 10−5 µg/µL and 7.051 ± 0.067 µg/µg chlorophyll a. Our results suggest the potential of F. diplosiphon as a robust species that can grow at varying temperatures ranging from 13 °C to 32 °C, while producing compounds for applications ranging from biofuel to nutritional supplements. The outcomes of this study pave the way for production-level scale-up and processing of F. diplosiphon-derived biofuels and marketable bioproducts. Fuel produced using this technology will be eco-friendly and cost-effective, and will make full use of the geographical location of regions with access to brackish waters. 
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    Free, publicly-accessible full text available March 1, 2024
  3. Free, publicly-accessible full text available January 1, 2024
  4. Fremyella diplosiphon is a well-studied a model cyanobacterium for photosynthesis due to its efficient light absorption potential and pigment accumulation. In the present study, the impact of ampicillin, tetracycline, kanamycin, and cefotaxime on pigment fluorescence and photosynthetic capacity in Fremyella diplosiphon strains B481-WT and B481-SD was investigated. Our results indicated that both strains exposed to kanamycin from 0.2 to 3.2 mg/L and tetracycline from 0.8 to 12.8 mg/L enhanced growth and pigment accumulation. Additionally, B481-SD treated with 0.2–51.2 mg/L ampicillin resulted in a significant enhancement of pigment fluorescence. A detrimental effect on growth and pigmentation in both the strains exposed to 6.4–102.5 mg/L kanamycin and 0.8–102.5 mg/L cefotaxime was observed. Detection of reactive oxygen species revealed highest levels of oxidative stress at 51.2 and 102.5 mg/L kanamycin for B481- SD and 102.5 mg/L for B481-WT. Membrane permeability detected by lactate dehydrogenase assay indicated maximal activity at 0.8 mg/L ampicillin, kanamycin, and tetracycline treatments on day 6. Abundant vacuolation, pyrophosphate, and cyanophycin granule formation were observed in treated cells as a response to antibiotic stress. These findings on the hormetic effect of antibiotics on F. diplosiphon indicate that optimal antibiotic concentrations induce cellular growth while high concentrations severely impact cellular functionality. Future studies will be aimed to enhance cellular lipid productivity at optimal antibiotic concentrations to disintegrate the cell wall, thus paving the way for clean bioenergy applications. 
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  5. Dr. Krishna Ganesh (Ed.)
    Nanoscale zero-valent iron nanoparticles (nZVIs) are known to boost biomass production and lipid yield in Fremyella diplosiphon, a model biodiesel-producing cyanobacterium. However, the impact of nZVI-induced reactive oxygen species (ROS) in F. diplosiphon has not been evaluated. In the present study, ROS in F. diplosiphon strains (B481-WT and B481-SD) generated in response to nZVI-induced oxidative stress were quantified and the enzymatic response determined. Lipid peroxidation as a measure of oxidative stress revealed significantly higher malondialdehyde content (p < 0.01) in both strains treated with 3.2, 12.8, and 51.2 mg L–1 nZVIs compared to untreated control. In addition, ROS in all nZVI-treated cultures treated with 1.6–25.6 mg L–1 nZVIs was significantly higher than the untreated control as determined by the 2′,7′-dichlorodihydrofluorescein diacetate fluorometric probe. Immunodetection using densitometric analysis of iron superoxide dismutase (SOD) revealed significantly higher SOD levels in both strains treated with nZVIs at 51.2 mg L–1. In addition, we observed significantly higher (p < 0.001) SOD levels in the B481-SD strain treated with 6.4 mg L−1 nZVIs compared to 3.2 mg L–1 nZVIs. Validation using transmission electron microscopy equipped with energy-dispersive X-ray spectroscopy (EDS) revealed adsorption of nZVIs with a strong iron peak in both B481-WT and B481-SD strains. While the EDS spectra showed strong signals for iron at 4 and 12 days after treatment, a significant decrease in peak intensity was observed at 20 days. Future efforts will be aimed at studying transduction mechanisms that cause metabolic and epigenetic alterations in response to nZVIs in F. diplosiphon. 
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