•Thermo-resistant Micractinium sp. and Scenedesmus sp. survive at 10–50°C.•Different temperature and nutrient regimes significantly alter lipid and FAME content.•Highest lipid productivity was ...obtained under P-depletion in Micractinium sp.•Diurnal temperature fluctuation increases lipid content in Micractinium sp.•Saturated fatty acid content increases with increasing temperature.
Despite the vast interest in microalgae as feedstock for biodiesel production, relatively few studies examined their response to diurnal temperature fluctuation. Here, we describe biomass and lipid productivities and fatty acid profiles of thermo-resistant Micractinium sp. and Scenedesmus sp. grown in batch cultures in a laboratory set-up that mimics a typically warm summer day in Central Anatolia with a 16-h light temperature of 30°C and 8-h dark temperature of 16°C (30°C (day)/16°C (night)). Both strains can survive a temperature range of 10–50°C. We found the lipid productivities of Micractinium sp. and Scenedesmus sp. as 30/21mgL−1d−1 and 6/7mgL−1d−1, respectively during the 30°C (day)/16°C (night) cycle. Saturated fatty acid content increased with increasing temperature. Additionally, we cultured Micractinium sp. under Nitrogen (N) and Phosphorus (P) limiting conditions. Highest lipid productivity of 85.4±2mgL−1d−1 was obtained under P-depletion during exponential growth phase. Oleic acid amount also increased eight fold during P-deplete.
The RNA-binding proteins FCA and FPA were identified based on their repression of the flowering time regulator FLC but have since been shown to have widespread roles in the Arabidopsis thaliana ...genome. Here, we use whole-genome tiling arrays to show that a wide spectrum of genes and transposable elements are misexpressed in the fca-9 fpa-7 (fcafpa) double mutant at two stages of seedling development. There was a significant bias for misregulated genomic segments mapping to the 3' region of genes. In addition, the double mutant misexpressed a large number of previously unannotated genomic segments corresponding to intergenic regions. We characterized a subset of these misexpressed unannotated segments and established that they resulted from extensive transcriptional read-through, use of downstream polyadenylation sites, and alternative splicing. In some cases, the transcriptional read-through significantly reduced expression of the associated genes. FCA/FPA-dependent changes in DNA methylation were found at several loci, supporting previous associations of FCA/FPA function with chromatin modifications. Our data suggest that FCA and FPA play important roles in the A. thaliana genome in RNA 3' processing and transcription termination, thus limiting intergenic transcription.
The realization that non-coding RNAs and antisense transcription are pervasive in many genomes has emphasized our relatively poor understanding of what limits transcription and how initiation and ...termination are linked to processing and turnover of the RNA. In genomes where the density of genes is high it is clearly important to efficiently terminate transcription to prevent read-through into adjacent genes. In a recent paper published in PNAS, we showed that two RNA binding proteins in Arabidopsis thaliana, FCA and FPA, play important roles in limiting intergenic transcription in the A. thaliana genome. Their absence leads to transcriptional read-through over many kilobases (kb), which influences expression, and in some cases chromatin modifications, of associated genes.
Gene activation in eukaryotes frequently involves interactions between chromosomal regions. We have investigated whether higher‐order chromatin structures are involved in the regulation of the ...Arabidopsis floral repressor gene FLC, a target of several chromatin regulatory pathways. Here, we identify a gene loop involving the physical interaction of the 5′ and 3′ flanking regions of the FLC locus using chromosome conformation capture. The FLC loop is unaffected by mutations disrupting conserved chromatin regulatory pathways leading to very different expression states. However, the loop is disrupted during vernalization, the cold‐induced, Polycomb‐dependent epigenetic silencing of FLC. Loop disruption parallels timing of the cold‐induced FLC transcriptional shut‐down and upregulation of FLC antisense transcripts, but does not need a cold‐induced PHD protein required for the epigenetic silencing. We suggest that gene loop disruption is an early step in the switch from an expressed to a Polycomb‐silenced state.
Arabidopsis flowering requires a cold spell (vernalization) involving downregulation of the FLC flowing repressor, which is linked to a gene loop between the 5′ and 3′ regions of the FLC locus. Loop formation is disrupted during cold exposure coinciding with downregulation of FLC expression and accumulation of antisense transcripts.
•Thermo-resistant microalgae isolated from geothermal flora of Central Anatolia.•Strains identified as Scenedesmus sp., Hindakia tetrachotoma and Micractinium sp.•All three isolates are adaptable to ...growth at a wide temperature range (25–50°C).•Superior properties of Micractinium sp. ME05 for biodiesel production.•Suitable FAME profile of Micractinium sp. ME05 &Scenedesmus sp. ME03 for biodiesel.
Oil content and composition, biomass productivity and adaptability to different growth conditions are important parameters in selecting a suitable microalgal strain for biodiesel production. Here, we describe isolation and characterization of three green microalgal species from geothermal flora of Central Anatolia. All three isolates, namely, Scenedesmus sp. METUNERGY1402 (Scenedesmus sp. ME02), Hindakia tetrachotoma METUNERGY1403 (H. tetrachotoma ME03) and Micractinium sp. METUNERGY1405 (Micractinium sp. ME05) are adaptable to growth at a wide temperature range (25–50°C). Micractinium sp. ME05, particularly has superior properties for biodiesel production. Biomass productivity, lipid content and lipid productivity of this isolate are 0.17gL−1d−1, 22.7% and 0.04gL−1d−1, respectively. In addition, Micractinium sp. ME05 and Scenedesmus sp. ME03 mainly contain desirable fatty acid methyl esters (i.e. 16:0, 16:1, 18:0 and 18:1) for biodiesel production. All isolates can further be improved via genetic and metabolic engineering strategies.
The human body can fight against the adverse effects of chronic exposure to environmental pollutants and stress by consumption of a diet rich in antioxidants. Although fruits and vegetables are the ...predominant sources, alternative sources of antioxidants such as microalgae are also being explored. Here, we investigate the antioxidant capacity, total phenolic, flavonoid, and carotenoid contents of novel thermo-resistant green microalga
Scenedesmus
sp. ME02. This strain has previously been shown to have a high polyunsaturated fatty acid content. Four different solvents were used for extraction and the antioxidant capacity was determined to be 3.71 ± 0.11 and 47.01 ± 3.14 μmol Trolox eq. g
−1
DW in ethanol/water mixture by 2,2-diphenyl-1-picrylhydrazyl (DPPH) and ferric reducing antioxidant power (FRAP) assays, respectively. Total phenolic, flavonoid, and carotenoid contents in ethanol/water were measured as 5.40 ± 0.28 mg gallic acid eq. g
−1
DW, 1.61 ± 0.76 mg quercetin eq. g
−1
DW, 0.61 ± 0.05 mg g
−1
, respectively. This is one of the few studies that reports the presence and quantification of total flavonoids in microalgae. The correlation between the total phenolic content and FRAP assay, but not the DPPH assay, was statistically significant. Finally, 12 different phenolic compounds were analyzed by reverse-phase HPLC and ethyl acetate extract showed substantial amounts of quercetin (0.84 ± 0.12 mg g
−1
DW) and rutin (0.11 ± 0.08 mg g
−1
DW). Quercetin amount was also high in the ethanol/water extract along with gallic acid, 4-hydroxy benzoic acid, and chlorogenic acid. To the best of our knowledge, this is the first study that reports significant amounts of quercetin and rutin in a microalgal species.
Oxidative stress damages cellular components and may lead to cell death when it is not effectively counterbalanced by the endogenous antioxidant mechanisms. Exogenous sources of antioxidants are also ...necessary to cope with high levels of free radicals. Microalgae are rich sources of diverse metabolites with high antioxidant potential. In this study, metabolites of Hindakia tetrachotoma ME03, a green microalga previously isolated from thermal springs in Türkiye, were chemically fractionated using four solvents (ethanol-water, ethyl acetate, hexane and water). The extracts were evaluated for their antioxidant capacities, total phenolics, flavonoids and carotenoids. The highest antioxidant capacity, phenolic and carotenoid contents were obtained in the ethanol-water extracts. The antioxidant capacity in the ethanol-water extracts was measured as 12.42 ± 1.21 μmol Trolox g
-1
DW and 67.98 ± 3.45 μmol Trolox g
-1
DW by DPPH and FRAP assays, respectively. Twelve different phenolic compounds in the ethanol-water and ethyl acetate extracts were quantified by reverse phase high pressure liquid chromatography. Quercetin and rutin were the most abundant phenolics in the ethanol-water extracts, whereas the ethyl acetate extract was rich in phenolic precursor, benzoic acid. Finally, the cytoprotective effect of ethanol-water extracts of H. tetrachotoma ME03 against H
2
O
2
-induced oxidative damage was investigated using an in vitro cell line model of human breast adenocarcinoma (MCF7). Hindakia tetrachotoma ME03 extracts significantly decreased the intracellular reactive oxygen species levels and the percentage of apoptotic and necrotic cells in MCF7 cells. These findings suggest the strong cytoprotective activity of H. tetrachotoma ME03 extracts, which may be conferred by its antioxidative properties.
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