Yoon-E Choi

Two-stage cultivation of two Chlorella sp. strains by simultaneous treatment of brewery wastewater and maximizing lipid productivity.

A cultivation system in the two-stage photoautotrophic-photoheterotrophic/mixotrophic mode was adapted to maximize lipid productivity of two freshwater strains of Chlorella sp. grown in brewery wastewater (BWW). The endogenous Chlorella sp. isolated from BWW had a higher growth rate than wild-type Chlorella vulgaris (UTEX-265) while C. vulgaris (UTEX-265) had a higher maximal biomass and lipid contents than that of endogenous Chlorella sp., resulting in more than 90% of the inorganic nutrients in both total nitrogen (TN) and phosphorus (TP) was removed during the first stage in the two-stage photoautotrophic-photoheterotrophic mode in each Chlorella sp. The maximal biomass and lipid contents of C. vulgaris (UTEX-265) for single stage photoautotrophic cultivation were 1.5 g/L and 18%, respectively. Importantly, during two-stage photoautotrophic-photoheterotrophic cultivation for C. vulgaris (UTEX-265), the biomass was increased to 3.5 g/L, and the lipid productivity was increased from 31.1 to 108.0mg/L day.

Direct lipid extraction from wet Chlamydomonas reinhardtii biomass using osmotic shock.

High-cost downstream process is a major bottleneck for producing microalgal biodiesel at reasonable price. Conventional lipid extraction process necessitates biomass drying process, which requires substantial amount of energy. In this regard, lipid extraction from wet biomass must be an attractive solution. However, it is almost impossible to recover lipid directly from wet microalgae with current technology. In this study, we conceived osmotic shock treatment as a novel method to extract lipid efficiently. Osmotic shock treatment was applied directly to wet Chlamydomonas reinhardtii biomass with water content >99%, along with both polar and non-polar organic solvents. Our results demonstrated that osmotic shock could increase lipid recovery approximately 2 times. We also investigated whether the presence of cell wall or different cell stages could have any impact on lipid recovery. Cell wall-less mutant stains and senescent cell phase could display significantly increased lipid recovery. Taken together, our results suggested that osmotic shock is a promising technique for wet lipid extraction from microalgal biomass and successfully determined that specific manipulation of biomass in certain cell phase could enhance lipid recovery further.

High-cell-density cultivation of oleaginous yeast Cryptococcus curvatus for biodiesel production using organic waste from the brewery industry.

Waste spent yeast from brewery industry was used as a sole growth substrate to grow an oleaginous yeast Cryptococcus curvatus for the purpose of biodiesel production. Approximately 7 g/l/d of biomass productivity was obtained using only spent yeast (30 g/l) without additional nutrients and pretreatment of any kind. To make best use of available nutrients in the spent yeast, stepwise cultivation was carried out in a batch culture mode and the highest biomass and lipid content, which were 50.4 g/l and 37.7%, respectively, were obtained at 35:1 of C/N ratio. Lipid from C. curvatus was found to be a quality-sufficient source of oil as a transportation fuel in terms of cetane, iodine values, and oxidation stability, although the values of cold filter plugging point were less desirable. Economic evaluation revealed that the use of the spent yeast could significantly reduce the unit cost of yeast-based biodiesel production.

Phytohormone Supplementation Significantly Increases Growth of Chlamydomonas reinhardtii Cultivated for Biodiesel Production

Cultivation is the most expensive step in the production of biodiesel from microalgae, and substantial research has been devoted to developing more cost-effective cultivation methods. Plant hormones (phytohormones) are chemical messengers that regulate various aspects of growth and development and are typically active at very low concentrations. In this study, we investigated the effect of different phytohormones on microalgal growth and biodiesel production in Chlamydomonas reinhardtii and their potential to lower the overall cost of commercial biofuel production. The results indicated that all five of the tested phytohormones (indole-3-acetic acid, gibberellic acid, kinetin, 1-triacontanol, and abscisic acid) promoted microalgal growth. In particular, hormone treatment increased biomass production by 54 to 69xa0% relative to the control growth medium (Tris–acetate–phosphate, TAP). Phytohormone treatments also affected microalgal cell morphology but had no effect on the yields of fatty acid methyl esters (FAMEs) as a percent of biomass. We also tested the effect of these phytohormones on microalgal growth in nitrogen-limited media by supplementation in the early stationary phase. Maximum cell densities after addition of phytohormones were higher than in TAP medium, even when the nitrogen source was reduced to 40xa0% of that in TAP medium. Taken together, our results indicate that phytohormones significantly increased microalgal growth, particularly in nitrogen-limited media, and have potential for use in the development of efficient microalgal cultivation for biofuel production.

A novel fed-batch process based on the biology of Aurantiochytrium sp. KRS101 for the production of biodiesel and docosahexaenoic acid

The biology of Aurantiochytrium sp. KRS101 was thoroughly investigated to enhance its production of biodiesel and docosahexaenoic acid (DHA). Nutrients and salinity were optimized to prevent biomass loss due to cell rupture. Calculation of yield coefficients showed that nitrogen was mostly responsible for the early stage of cell growth or division, whereas carbon was necessary for the entire process of cell development, particularly cell enlargement during late stages. Using these distinctive yield coefficients, a modified fed-batch cultivation method was designed, resulting in increases in palmitic acid (PA) and DHA production of up to 137% and 29%, respectively. This modified fed-batch cultivation method, using appropriate supplies of nitrogen and carbon, may improve the yields of PA and DHA, thus expanding the biotechnological applications of Aurantiochytrium sp. KRS101.

Eruca sativa and its Flavonoid Components, Quercetin and Isorhamnetin, Improve Skin Barrier Function by Activation of Peroxisome Proliferator-Activated Receptor (PPAR)-α and Suppression of Inflammatory Cytokines

Atopic dermatitis, which is related to dermatologic disorders and is associated with skin barrier dysfunction, represents an epidemic problem demanding effective therapeutic strategies. In the present study, we showed that the treatment with Eruca sativa extract resulted in a significant increase in the transactivation activity of peroxisome proliferator‐activated receptor (PPAR) response element such as PPAR‐α and suppression in the expression of inflammatory cytokine and antimicrobial peptides. In addition, E. sativa extract promotes the expression of filaggrin related to skin barrier protection. Quercetin and isorhamnetin, flavonoids constituents of E. sativa, also promoted PPAR‐α activity. These results indicate that E. sativa extract may be an appropriate material for improving skin barrier function as a skin therapeutic agent for atopic dermatitis. Copyright

Manipulation of light wavelength at appropriate growth stage to enhance biomass productivity and fatty acid methyl ester yield using Chlorella vulgaris

LEDs light offer several advantages over the conventional lamps, thereby being considered as the optimal light sources for microalgal cultivation. In this study, various light-emitting diodes (LEDs) especially red and blue color with different light wavelengths were employed to explore the effects of light source on phototrophic cultivation of Chlorella vulgaris. Blue light illumination led to significantly increased cell size, whereas red light resulted in small-sized cell with active divisions. Based on the discovery of the effect of light wavelengths on microalgal biology, we then applied appropriate wavelength at different growth stages; blue light was illuminated first and then shifted to red light. By doing so, biomass and lipid productivity of C. vulgaris could be significantly increased, compared to that in the control. These results will shed light on a novel approach using LED light for microalgal biotechnology.

Comparative proteomics using lipid over-producing or less-producing mutants unravels lipid metabolisms in Chlamydomonas reinhardtii

In this study, proteomic approach was employed to advance our understanding of genes associated with microalgal lipid production. We first generated random mutants of Chlamydomonas reinhardtii, which displayed increased or decreased lipid content, compared to that in the wild-type. Mutants were designated as CR12 and CR48. Then, the changes of protein expression associated with the mutations of Chlamydomonas reinhardtii were analyzed. We could identify proteins that were significantly up-regulated or down-regulated either in the wild-type or CR12 or CR48. Our results will help understand additional genes or pathways directly or indirectly linked to microalgal lipid production.

Protein phosphatase 2A regulatory subunits perform distinct functional roles in the maize pathogen Fusarium verticillioides

Fusarium verticillioides is a pathogen of maize causing ear rot and stalk rot. The fungus also produces fumonisins, a group of mycotoxins linked to disorders in animals and humans. A cluster of genes, designated FUM genes, plays a key role in the synthesis of fumonisins. However, our understanding of the regulatory mechanism of fumonisin biosynthesis is still incomplete. We have demonstrated previously that Cpp1, a protein phosphatase type 2A (PP2A) catalytic subunit, negatively regulates fumonisin production and is involved in cell shape maintenance. In general, three PP2A subunits, structural A, regulatory B and catalytic C, make up a heterotrimer complex to perform regulatory functions. Significantly, we identified two PP2A regulatory subunits in the F.u2009verticillioides genome, Ppr1 and Ppr2, which are homologous to Saccharomyces cerevisiaeu2005Cdc55 and Rts1, respectively. In this study, we hypothesized that Ppr1 and Ppr2 are involved in the regulation of fumonisin biosynthesis and/or cell development in F.u2009verticillioides, and generated a series of mutants to determine the functional role of Ppr1 and Ppr2. The PPR1 deletion strain (Δppr1) resulted in drastic growth defects, but increased microconidia production. The PPR2 deletion mutant strain (Δppr2) showed elevated fumonisin production, similar to the Δcpp1 strain. Germinating Δppr1 conidia formed abnormally swollen cells with a central septation site, whereas Δppr2 showed early hyphal branching during conidia germination. A kernel rot assay showed that the mutants were slow to colonize kernels, but this is probably a result of growth defects rather than a virulence defect. Results from this study suggest that two PP2A regulatory subunits in F.u2009verticillioides carry out distinct roles in the regulation of fumonisin biosynthesis and fungal development.

Cloning and characterization of a thermostable endo-arabinanase from Phanerochaete chrysosporium and its synergistic action with endo-xylanase

Putative arabinanase (PcARA) was cloned from cDNA of Phanerochaete chrysosporium. The gene sequencing indicated that PcARA consisted of 939 nucleotides that encodes for 312 amino acid arabinanase-polypeptide chain, including a signal peptide of 19 amino acids. Three-dimensional homology indicated that this enzyme is a five-bladed β-propeller, belonging to glycosidase family 43 and its secondary structure is consisted of 24 β-sheets. The PcARA-cDNA was expressed in Pichia pastoris using pPICZαC. SDS-PAGE of purified arabinanase showed a single band of 33xa0kDa that is very close to theoretical molecular mass of 33.9xa0kDa calculated by its amino acid content. Recombinant arabinanase (rPcARA) exhibited maximum activity at pH and temperature of 5.0 and 60xa0°C, respectively. End-product analysis of debranched arabinan hydrolysis by thin-layer chromatography indicated that rPcARA acted as endo-type. The synergistic action of rPcARA with recombinant xylanase resulted in 72 and 9.3xa0% release of total soluble sugar of arabinoxylan and NaOH-pretreated barley straw, respectively.