Publications by authors named "You-Kwan Oh"

77 Publications

Corrigendum to 'Supply of proton enhances CO electrosynthesis for acetate and volatile fatty acid productions' [Bioresour. Technol. 320(Part A) (2021) 124245-124253/Article 124245].

Bioresour Technol 2021 May 27:125293. Epub 2021 May 27.

Department of Chemical and Biomolecular Engineering, Pusan National University, Geumjeong-Gu, Busan 46241, Republic of Korea. Electronic address:

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http://dx.doi.org/10.1016/j.biortech.2021.125293DOI Listing
May 2021

Correlation of microbial community with salinity and nitrogen removal in an anammox-based denitrification system.

Chemosphere 2021 Jan 14;263:128340. Epub 2020 Sep 14.

Department of Microbiology, Pusan National University, Busan, 46241, Republic of Korea. Electronic address:

Anaerobic ammonium oxidation (anammox), a low-energy-consuming technology, can be used to remove nitrogen from industrial saline wastewater. However, high salinity inhibits anammox microbial activity. This study investigated the effect of salinity on nitrogen removal performance and microbial community structure. The experiment used an up-flow anammox reactor fed with synthetic wastewater with salinity increased from 0.5 to 2.5%. Results indicated that 80% nitrogen removal efficiency can be achieved at 2% salinity with a nitrogen loading rate of 2.0 kg-N/m/d. Anammox performance significantly deteriorated at 2.5% salinity. High-throughput sequencing revealed that Planctomycetes (representative anammox bacteria) increased with salinity, replacing Proteobacteria (representative heterotrophic denitrifying bacteria) in the microbial community. qPCR analysis indicated that relative abundance of "Candidatus Kuenenia" within anammox bacteria increased from 3.96 to 83.41%, corresponding to salinity of 0.5-2.0%, and subsequently decreased to 63.27% at 2.5% salinity, correlating with nitrogen-removal performance. Thus, anammox has potential in nitrogen removal from wastewater with salinity up to 2%.
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http://dx.doi.org/10.1016/j.chemosphere.2020.128340DOI Listing
January 2021

Enabling anoxic acetate assimilation by electrode-driven respiration in the obligate aerobe, Pseudomonas putida.

Bioelectrochemistry 2021 Apr 3;138:107690. Epub 2020 Nov 3.

School of Chemical Engineering, Pusan National University, 63 Busandeahak-ro, Geumjeong-Gu, Busan 46241, Republic of Korea. Electronic address:

This study examined the obligate aerobe, Pseudomonas putida, using acetate as the sole carbon and energy source, and respiration via an anode as the terminal electron acceptor under anoxic conditions. P. putida showed significantly different acetate assimilation in a closed-circuit microbial fuel cell (CC-MFC) compared to an open circuit MFC (OC-MFC). More than 72% (2.6 mmol) of acetate was consumed during 84 hrs in the CC-MFC in contrast to the no acetate consumption observed in the OC-MFC. The CC-MFC produced 150 μA (87 C) from acetate metabolization. Electrode-based respiration reduced the NADH/NAD ratio anaerobically, which is similar to the aerobic condition. The CC-MFC showed significantly higher acetyl-CoA synthetase activity than the OC-MFC (0.028 vs. 0.001 μmol/min/mg), which was comparable to the aerobic condition (circa 60%). Overall, electrode-based respiration enables P. putida to metabolize acetate under anoxic conditions and provide a platform to regulate the bacterial redox balance without oxygen.
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http://dx.doi.org/10.1016/j.bioelechem.2020.107690DOI Listing
April 2021

Recent developments and key barriers to microbial CO electrobiorefinery.

Bioresour Technol 2021 Jan 2;320(Pt A):124350. Epub 2020 Nov 2.

Gwangju Bio/Energy R&D Center, Korea Institute of Energy Research, Gwangju 61003, Republic of Korea. Electronic address:

The electrochemical conversion of CO can include renewable surplus electricity storage and CO utilisation. This review focuses on the microbial CO electrobiorefinery based on microbial electrosynthesis (MES) which merges electrochemical and microbial conversion to produce biofuels and higher-value chemicals. In this review, recent developments are discussed about bioelectrochemical conversion of CO into biofuels and chemicals in MES via microbial CO-fixation and electricity utilisation reactions. In addition, this review examines technical approaches to overcome the current limitations of MES including the following: engineering of the biocathode, application of electron mediators, and reactor optimisation, among others. An in-depth discussion of strategies for the CO electrobiorefinery is presented, including the integration of the biocathode with inorganic catalysts, screening of novel electroactive microorganisms, and metabolic engineering to improve target productivity from CO.
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http://dx.doi.org/10.1016/j.biortech.2020.124350DOI Listing
January 2021

Photoautotrophic hydrogen production of Rhodobacter sphaeroides in a microbial electrosynthesis cell.

Bioresour Technol 2021 Jan 29;320(Pt A):124333. Epub 2020 Oct 29.

School of Chemical and Biomolecular Engineering, Pusan National University, Busan 46241, Republic of Korea. Electronic address:

Conventional photoheterotrophic H production by purple sulfur bacteria requires additional organic substrates as the carbon and energy sources. This study examined the novel photoautotrophic H production of Rhodobacter sphaeroides with concomitant CO uptake in microbial electrosynthesis (MES). Under an applied potential of -0.9 V vs. Ag/AgCl to the cathode, Rhodobacter sphaeroides produced hydrogen with CO as the sole carbon source under illumination. The initial planktonic cells decreased rapidly in suspension, whereas biomass formation on the cathode surface increased gradually during MES operation. The electron and carbon flow under photoautotrophic conditions in MES were estimated. Glutamate, as the nitrogen source, enhanced hydrogen production significantly (328 mL/L/day) compared to NHCl (67 mL/L/day) during seven days of operation. The photoautotrophic condition with 6000 lx presented CO consumption and simultaneous biomass formation on the cathode electrode. MES-driven electron and proton transfer enabled the simultaneous production of hydrogen and CO uptake
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http://dx.doi.org/10.1016/j.biortech.2020.124333DOI Listing
January 2021

Supply of proton enhances CO electrosynthesis for acetate and volatile fatty acid productions.

Bioresour Technol 2021 Jan 16;320(Pt A):124245. Epub 2020 Oct 16.

School of Chemical Engineering, Pusan National University, Geumjeong-Gu, Busan 46241, Republic of Korea. Electronic address:

The microbial electrosynthesis is a platform to supply protons and electrons to improve the conversion efficiency and production rate for the valorization of C1 gas. This study examined proton migration and electron transfer of the electrode and microbe by using various external parameters in the electrosynthesis of CO. The CO electrosynthesis achieved almost double of coulombic efficiency than the conventional CO electrosynthesis. The maximum volumetric acetate production rate was 0.71 g/L/day in the BES, which was 2-6 times higher than reported elsewhere. These results show that the efficient proton migration and electron transfer can enhance the productivity and conversion efficiency of the biological CO conversion in a bioelectrochemical system.
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http://dx.doi.org/10.1016/j.biortech.2020.124245DOI Listing
January 2021

Effects of Nitrogen Supplementation Status on CO Biofixation and Biofuel Production of the Promising Microalga sp. ABC-001.

J Microbiol Biotechnol 2020 Aug;30(8):1235-1243

Department of Chemical and Biomolecular Engineering, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 34141, Republic of Korea.

The use of microalgal biomass as feedstock for biofuels has been discussed for decades as it provides a sustainable approach to producing fuels for the future. Nonetheless, its feasibility has not been established yet and various aspects of biomass applications such as CO biofixation should also be explored. Therefore, in this study, the CO biofixation and lipid/carbohydrate production potential of sp. ABC-001 were examined under various nitrogen concentrations. The highest biomass productivity and CO biofixation rate of 0.422 g/l/d and 0.683 g/l/d, respectively, were achieved under a nitrogen-rich condition (15 mM nitrate). Carbohydrate content was generally proportional to initial nitrate concentration and showed the highest value of 41.5% with 15 mM. However, lipid content showed an inverse relationship with nitrogen supplementation and showed the highest value of 47.4% with 2.5 mM. In consideration as feedstock for biofuels (bioethanol, biodiesel, and biogas), the sum of carbohydrate and lipid contents were examined and the highest value of 79.6% was achieved under low nitrogen condition (2.5 mM). For lipid-based biofuel production, low nitrogen supplementation should be pursued. However, considering the lower feasibility of biodiesel, pursuing CO biofixation and the production of carbohydrate-based fuels under nitrogenrich condition might be more rational. Thus, nitrogen status as a cultivation strategy must be optimized according to the objective, and this was confirmed with the promising alga sp. ABC-001.
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http://dx.doi.org/10.4014/jmb.2005.05039DOI Listing
August 2020

Enhancement of astaxanthin production by Haematococcus pluvialis using magnesium aminoclay nanoparticles.

Bioresour Technol 2020 Jul 29;307:123270. Epub 2020 Mar 29.

Department of Chemical & Biomolecular Engineering, Pusan National University (PNU), Busan 46241, Republic of Korea. Electronic address:

Improving the content and production of high-value ketocarotenoid pigments is critical for the commercialization of microalgal biorefineries. This study reported the use of magnesium aminoclay (MgAC) nanoparticles for enhancement of astaxanthin production by Haematococcus pluvialis in photoautotrophic cultures. Addition of 1.0 g/L MgAC significantly promoted cellular astaxanthin biosynthesis (302 ± 69 pg/cell), presumably by inducing tolerable oxidative stress, corresponding to a 13.7-fold higher production compared to that in the MgAC-untreated control (22 ± 2 pg/cell). The lipid content and cell size of H. pluvialis improved by 13.6- and 2.1-fold, respectively, compared to that of the control. Despite reduced cell numbers, the overall astaxanthin production (10.3 ± 0.4 mg/L) improved by 40% compared to the control (7.3 ± 0.6 mg/L), owing to improved biomass production. However, an MgAC dosage above 1.0 g/L inhibited biomass production by inducing electrostatic cell wall destabilization and aggregation. Therefore, MgAC-induced stimulation of algae varies widely based on their morphological and physiological characteristics.
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http://dx.doi.org/10.1016/j.biortech.2020.123270DOI Listing
July 2020

Biocompatible liquid-type carbon nanodots (C-paints) as light delivery materials for cell growth and astaxanthin induction of Haematococcus pluvialis.

Mater Sci Eng C Mater Biol Appl 2020 Apr 28;109:110500. Epub 2019 Nov 28.

Division of Material Analysis and Research, Korea Basic Science Institute, Daejeon 305-333, Republic of Korea. Electronic address:

In this study, we aimed to demonstrate the feasibility of the application of biocompatible liquid type fluorescent carbon nanodots (C-paints) to microalgae by improving microalgae productivity. C-paints were prepared by a simple process of ultrasound irradiation using polyethylene glycol (PEG) as a passivation agent. The resulting C-paints exhibited a carbonyl-rich surface with good uniformity of particle size, excellent water solubility, photo-stability, fluorescence efficiency, and good biocompatibility (<10.0 mg mL of C-paints concentration). In the practical application of C-paints to microalgae culture, the most effective and optimized condition leading to growth promoting effect was observed at a C-paints concentration of 1.0 mg mL (>20% higher than the control cell content). A C-paints concentration of 1-10.0 mg mL induced an approximately >1.8 times higher astaxanthin content than the control cells. The high light delivery effect of non-cytotoxic C-paints was applied as a stress condition for H. pluvialis growth and was found to play a major role in enhancing productivity. Notably, the results from this study are an essential approach to improve astaxanthin production, which can be used in various applications because of its therapeutic effects such as cancer prevention, anti-inflammation, immune stimulation, and treatment of muscle-soreness.
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http://dx.doi.org/10.1016/j.msec.2019.110500DOI Listing
April 2020

Recovery of Astaxanthin-Containing Oil from Haematococcus pluvialis by Nano-dispersion and Oil Partitioning.

Appl Biochem Biotechnol 2020 Apr 21;190(4):1304-1318. Epub 2019 Nov 21.

Biomass and Waste Energy Laboratory, Korea Institute of Energy Research, Daejeon, 34129, Republic of Korea.

The feasibilities of cell disruption by homogenization-assisted high-pressure nano-dispersion and recovery of astaxanthin-containing oil by oil partitioning in oil-acetone-water solution were examined. The total fatty acid content of Haematococcus pluvialis was 414.6 mg/g cell, and the astaxanthin content was 4.4% of oil. Extra oil was added to the solution in order to recover oil through instability of dispersion status instead of solvent evaporation. A total amount of energy of 0.34 kWh/L was consumed for acetone evaporation at 50 °C, whereas fully 1.86 kWh/L of energy for water evaporation was consumed. When soybean oil was added to the solution after partial acetone evaporation, the oil-recovery yield was 97.8%, while the yield after full evaporation was 97.6% in 10-g/L solution. However, the energy consumed for partial evaporation (0.29 kWh/L) was much lower than that for full evaporation (0.40 kWh/L). When H. pluvialis oil was added to the solution after partial evaporation, the oil-recovery yield decreased to 90.6% due to the impurity of crude H. pluvialis oil in 10-g/L solution. Methods such as refining of H. pluvialis oil, increase of microalgae dosage for cell disruption, and increase of the injection amount of extra oil can help to enhance oil recovery.
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http://dx.doi.org/10.1007/s12010-019-03167-yDOI Listing
April 2020

Rapid induction of edible lipids in Chlorella by mild electric stimulation.

Bioresour Technol 2019 Nov 2;292:121950. Epub 2019 Aug 2.

School of Chemical & Biomolecular Engineering, Pusan National University, Busan 46241, Republic of Korea. Electronic address:

In this work, a new stress-based method for rapid induction of triacylglycerol (TAG) and total and polyunsaturated fatty acid accumulations in Chlorella sp. by mild electric stimulation is presented. When a cathodic current of 31 mA (voltage: 4 V) was applied to the algal cells for 4 h, the TAG content of the electro-treated cells was sharply increased to a level 2.1 times that of the untreated control. The contents of the polyunsaturated linoleic (C18:2n6) and linolenic (C18:3n3) acids in the electro-treated cells were also 36 and 57% higher than those in the untreated cells, respectively. Cyclic voltammetry and various biochemical analyses indicate that TAG and fatty acid formations are electro-stimulated via de novo fatty acid biosynthesis and metabolic transformation in the Chlorella cells.
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http://dx.doi.org/10.1016/j.biortech.2019.121950DOI Listing
November 2019

High-efficiency cell disruption and astaxanthin recovery from Haematococcus pluvialis cyst cells using room-temperature imidazolium-based ionic liquid/water mixtures.

Bioresour Technol 2019 Feb 23;274:120-126. Epub 2018 Nov 23.

Climate Change Research Division, Korea Institute of Energy Research, Daejeon 34129, Republic of Korea. Electronic address:

Energy-saving, high-efficiency cell disruption is a critical step for recovery of thermolabile antioxidant astaxanthin from Haematococcus pluvialis cyst cells of rigid cell-wall structure. In this study, as room-temperature green solvents, 10 types of 1-ethyl-3-methylimidazolium ([Emim])-based ionic liquids (ILs) were compared and evaluated for their abilities to disrupt H. pluvialis cyst cells for astaxanthin/lipid extraction. Among the 10 ILs tested, 3 [Emim]-based ILs with HSO, CHSO, and (CFSO)N anions were selected based on astaxanthin/lipid extraction performance and synthesis cost. When pretreated with IL/water mixtures, intact cyst cells were significantly torn, broken or shown to release cytoplasmic components, thereby facilitating subsequent separation of astaxanthin/lipid by hexane. However, excess IL pretreatments at high temperature/IL dosages and longer incubation times significantly deteriorated lipid and/or astaxanthin. Under optimized mild conditions (6.7% (v/v) IL in water solution, 30 °C, 60 min), almost complete astaxanthin recoveries (>99%) along with moderate lipid extractions (∼82%) could be obtained.
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http://dx.doi.org/10.1016/j.biortech.2018.11.082DOI Listing
February 2019

Studies on mass production and highly solar light photocatalytic properties of gray hydrogenated-TiO sphere photocatalysts.

J Hazard Mater 2018 Sep 25;358:222-233. Epub 2018 Jun 25.

Advanced Nano-surface Research Group, Korea Basic Science Institute, Daejeon 34133, Republic of Korea. Electronic address:

In this paper, it is first reported that gray hydrogenated TiO sphere photocatalysts (H-TiO) with high reactivity to solar light are mass produced within a few minutes using an underwater discharge plasma modified sol-gel method at room temperature and atmospheric pressure. This plasma modified system is an easy one-step in-situ synthetic process and the crystallinity, hydrogenation, and spherical structure of H-TiO are achieved by the synergy effect between the continuous reaction of highly energetic atomic and molecular species generated from the underwater plasma and surface tension of water. The resultant H-TiO demonstrated high anatase/rutile bicrystallinity and extended optical absorption spectrum from the ultraviolet (UV) to visible range. Furthermore, various defects including oxygen vacancies and hydroxyl species on the TiO surface permitted the enhancement of the photocatalytic performance. It was demonstrated that H-TiO photocatalysts showed significant degradation efficiencies for reactive black 5 (RB 5), rhodamine B (Rho B), and phenol (Ph) under solar light irradiation, up to approximately 5 times higher than that of commercial anatase TiO (C-TiO), which resulted in good water purification. Notably, it was also possible to cultivate HepG2 cells using such well-purified water (to degrees up to 76%), with minimal cytotoxicity. Considering all these results, we believe that this novel plasma technology is promising for important environmental applications.
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http://dx.doi.org/10.1016/j.jhazmat.2018.06.055DOI Listing
September 2018

Effects of in Medical Therapeutics: A Systematic Review and Meta-Analysis of Randomized Controlled Trials.

Int J Mol Sci 2018 May 16;19(5). Epub 2018 May 16.

Department of BioNano Technology, Gachon University, 1342 Seongnam-Daero, Sujeong-Gu, Seongnam-Si, Gyeonggi-do 13120, Korea.

In this study, we investigated the therapeutic potential and medical applications of () by conducting a systematic review of the existing literature and performing a meta-analysis. The original efficacy treatment of the mushroom extract is considered primarily and searched in electronic databases. A total of 623 articles were assessed, 33 randomized controlled experiments were included after the manual screening, and some papers, review articles, or editorials that did not contain data were excluded. A comparative standard means difference (SMD) and a funnel plot between control and groups were used as parameters to demonstrate the beneficial effects of for diabetes and cancer treatment, as well as anti-inflammatory, anti-fungal and antioxidant activities. The meta-analysis was carried out using Review Manager 5.1 software. Although for therapeutic diabetes there was heterogeneity in the subgroup analysis (I² = 91.9%), the overall results showed statistically significant SMDs in major symptoms that decreased serum insulin levels (SMD = 1.92, 95% CI (1.10, 2.75), I² = 0%), wound rates (SMD = 3.55 (2.56, 4.54), I² = 40%) and contributions to an increase in nutrient intake content (SMD = 0.32 (-0.15, 0.78), I² = 0%). Simultaneously, the study confirmed the utility of treatment in terms of not only anti-cancer activity (reduction of tumor activity and survival of cancer cells I² = 42 and 34%, respectively) but also anti-inflammatory, anti-fungal and antioxidant activities (I² = 50, 44, and 10%, respectively). Our findings suggest that extracts are useful for prevention and treatment of human diseases and might be the best candidates for future medicines.
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http://dx.doi.org/10.3390/ijms19051487DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5983641PMC
May 2018

Co-culture-based biological carbon monoxide conversion by Citrobacter amalonaticus Y19 and Sporomusa ovata via a reducing-equivalent transfer mediator.

Bioresour Technol 2018 Jul 2;259:128-135. Epub 2018 Mar 2.

School of Chemical and Biomolecular Engineering, Pusan National University, 63 Busandeahak-ro, Geumjeong-Gu, Busan 46241, Republic of Korea. Electronic address:

The biological conversion of carbon monoxide (CO) has been highlighted for the development of a C1 gas biorefinery process. Despite this, the toxicity and low reducing equivalent of CO uptake make biological conversion difficult. The use of synthetic co-cultures is an alternative way of enhancing the performance of CO bioconversion. This study evaluated a synthetic co-culture consisting of Citrobacter amalonaticus Y19 and Sporomusa ovata for acetate production from CO. In this consortium, the CO and H produced by the water-gas shift reaction of C. amalonaticus Y19, were utilized further by S. ovata. Higher acetate production was achieved in the co-culture system compared to the monoculture counterparts. Furthermore, syntrophic cooperation via various reducing equivalent carriers provided new insights into the synergistic metabolic benefits with a toxic and refractory substrate, such as CO. This study also suggests an appropriate model for examining the syntrophic interaction between microbial species in a mixed community.
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http://dx.doi.org/10.1016/j.biortech.2018.02.129DOI Listing
July 2018

Recent developments and key barriers to advanced biofuels: A short review.

Bioresour Technol 2018 Jun 21;257:320-333. Epub 2018 Feb 21.

Gwangju Bioenergy R&D Center, Korea Institute of Energy Research, Gwangju 61003, Republic of Korea. Electronic address:

Biofuels are regarded as one of the most viable options for reduction of CO emissions in the transport sector. However, conventional plant-based biofuels (e.g., biodiesel, bioethanol)'s share of total transportation-fuel consumption in 2016 was very low, about 4%, due to several major limitations including shortage of raw materials, low CO mitigation effect, blending wall, and poor cost competitiveness. Advanced biofuels such as drop-in, microalgal, and electro biofuels, especially from inedible biomass, are considered to be a promising solution to the problem of how to cope with the growing biofuel demand. In this paper, recent developments in oxy-free hydrocarbon conversion via catalytic deoxygenation reactions, the selection of and lipid-content enhancement of oleaginous microalgae, electrochemical biofuel conversion, and the diversification of valuable products from biomass and intermediates are reviewed. The challenges and prospects for future development of eco-friendly and economically advanced biofuel production processes also are outlined herein.
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http://dx.doi.org/10.1016/j.biortech.2018.02.089DOI Listing
June 2018

Manganese and cobalt recovery by surface display of metal binding peptide on various loops of OmpC in Escherichia coli.

J Ind Microbiol Biotechnol 2018 01 28;45(1):31-41. Epub 2017 Nov 28.

Department of Chemical Engineering, University of Ulsan, Ulsan, 44610, Republic of Korea.

In a cell-surface display (CSD) system, successful display of a protein or peptide is highly dependent on the anchoring motif and the position of the display in that anchoring motif. In this study, a recombinant bacterial CSD system for manganese (Mn) and cobalt (Co) recovery was developed by employing OmpC as an anchoring motif on three different external loops. A portion of Cap43 protein (TRSRSHTSEG) was employed as a manganese and cobalt binding peptide (MCBP), which was fused with OmpC at three different external loops. The fusions were made at the loop 2 [fusion protein-2 (FP2)], loop 6 (FP6), and loop 8 (FP8) of OmpC, respectively. The efficacy of the three recombinant strains in the recovery of Mn and Co was evaluated by varying the concentration of the respective metal. Molecular modeling studies showed that the short trimeric repeats of peptide probably form a secondary structure with OmpC, thereby giving rise to a difference in metal recovery among the three recombinant strains. Among the three recombinant strains, FP6 showed increased metal recovery with both Mn and Co, at 1235.14 (1 mM) and 379.68 (0.2 mM) µmol/g dry cell weight (DCW), respectively.
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http://dx.doi.org/10.1007/s10295-017-1989-xDOI Listing
January 2018

Microalgae dewatering based on forward osmosis employing proton exchange membrane.

Bioresour Technol 2017 Nov 17;244(Pt 1):57-62. Epub 2017 Jul 17.

Department of Civil and Environmental Engineering, Korea Advanced Institute of Science and Technology, 291 Daehak-ro, Yuseong-gu, Daejeon 34141, Republic of Korea. Electronic address:

In this study, electrically-facilitated forward osmosis (FO) employing proton exchange membrane (PEM) was established for the purpose of microalgae dewatering. An increase in water flux was observed when an external voltage was applied to the FO equipped with the PEM; as expected, the trend became more dramatic with both concentration of draw solution and applied voltage raised. With this FO used for microalgae dewatering, 247% of increase in flux and 86% in final biomass concentration were observed. In addition to the effect on flux improvement, the electrically-facilitated FO exhibited the ability to remove chlorophyll from the dewatered biomass, down to 0.021±0015mg/g cell. All these suggest that the newly suggested electrically-facilitated FO, one particularly employed PEM, can indeed offer a workable way of dewatering of microalgae; it appeared to be so because it can also remove the ever-problematic chlorophyll from extracted lipids in a simultaneous fashion.
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http://dx.doi.org/10.1016/j.biortech.2017.07.086DOI Listing
November 2017

Effect of salt type and concentration on the growth and lipid content of Chlorella vulgaris in synthetic saline wastewater for biofuel production.

Bioresour Technol 2017 Nov 17;243:147-153. Epub 2017 Jun 17.

Department of Civil, Environmental, and Construction Engineering, University of Central Florida, Orlando, FL 32816, USA. Electronic address:

Microalgae can offer several benefits for wastewater treatment with their ability to produce large amounts of lipids for biofuel production and the high economic value of harvested biomass for biogas and fertilizer. This study found that salt concentration (∼45gL) had more of an effect than salt type on metabolisms of Chlorella vulgaris for wastewater treatment and biofuel production. Salinity stress decreased the algal growth rate in wastewater by 0.003daypermScm and slightly reduced nutrient removal rates. However, salinity stress was shown to increase total lipid content from 11.5% to 16.1% while also increasing the saturated portions of fatty acids in C. vulgaris. In addition, salinity increased the algal settling rate from 0.06 to 0.11mday which could potentially reduce the cost of harvesting for algal biofuel production. Overall, C. vulgaris makes a suitable candidate for high salinity wastewater cultivation and biofuel production.
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http://dx.doi.org/10.1016/j.biortech.2017.06.081DOI Listing
November 2017

Cell disruption and lipid extraction for microalgal biorefineries: A review.

Bioresour Technol 2017 Nov 12;244(Pt 2):1317-1328. Epub 2017 Jun 12.

Biomass and Waste Energy Laboratory, Korea Institute of Energy Research, Daejeon 34129, Republic of Korea. Electronic address:

The microalgae-based biorefinement process has attracted much attention from academic and industrial researchers attracted to its biofuel, food and nutraceutical applications. In this paper, recent developments in cell-disruption and lipid-extraction methods, focusing on four biotechnologically important microalgal species (namely, Chlamydomonas, Haematococcus, Chlorella, and Nannochloropsis spp.), are reviewed. The structural diversity and rigidity of microalgal cell walls complicate the development of efficient downstream processing methods for cell-disruption and subsequent recovery of intracellular lipid and pigment components. Various mechanical, chemical and biological cell-disruption methods are discussed in detail and compared based on microalgal species and status (wet/dried), scale, energy consumption, efficiency, solvent extraction, and synergistic combinations. The challenges and prospects of the downstream processes for the future development of eco-friendly and economical microalgal biorefineries also are outlined herein.
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http://dx.doi.org/10.1016/j.biortech.2017.06.038DOI Listing
November 2017

Acidified-flocculation process for harvesting of microalgae: Coagulant reutilization and metal-free-microalgae recovery.

Bioresour Technol 2017 Sep 5;239:190-196. Epub 2017 May 5.

Biomass and Waste Energy Laboratory, Korea Institute of Energy Research, 152 Gajeong-ro, Yuseong-gu, Daejeon 34129, Republic of Korea. Electronic address:

Chemical flocculation is considered to be an overall low-cost and up-scalable process for harvesting of microalgae. In this study a new flocculation approach utilizing metal coagulant (Fe(SO)) and sulfuric acid (HSO) was introduced for harvesting of Chlorella sp. KR-1, which overcome two main issues of contamination and reuse of coagulant. Reduction of pH successfully released precipitates attached to the microalgae, and the remaining acidic solution containing recovered ferric ions could be reused for harvesting up to three times with high, better-than 98% efficiencies. Moreover, the acid-treated microalgal biomass could be directly used for lipid extraction without additional catalyst. High extraction yields of around 32% were achieved with FAME conversion efficiencies of around 90%. The integrated approach devised in the present study is expected to make the best use of the age-old yet effective harvesting means of flocculation, which can be a practical and economical option in microalgal biorefinery.
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http://dx.doi.org/10.1016/j.biortech.2017.05.021DOI Listing
September 2017

Mild pressure induces rapid accumulation of neutral lipid (triacylglycerol) in Chlorella spp.

Bioresour Technol 2016 Nov 7;220:661-665. Epub 2016 Sep 7.

Biomass and Waste Energy Laboratory, Korea Institute of Energy Research, Daejeon 34129, Republic of Korea. Electronic address:

Effective enhancement of neutral lipid (especially triacylglycerol, TAG) content in microalgae is an important issue for commercialization of microalgal biorefineries. Pressure is a key physical factor affecting the morphological, physiological, and biochemical behaviors of organisms. In this paper, we report a new stress-based method for induction of TAG accumulation in microalgae (specifically, Chlorella sp. KR-1 and Ch. sp. AG20150) by very-short-duration application of mild pressure. Pressure treatments of 10-15bar for 2h resulted in a considerable, ∼55% improvement of the 10-100g/Lcells' TAG contents compared with the untreated control. The post-pressure-treatment increase of cytoplasmic TAG granules was further confirmed by transmission electron microscopy (TEM). Notwithstanding the increased TAG content, the total lipid content was not changed by pressurization, implying that pressure stress possibly induces rapid remodeling/transformation of algal lipids rather than de novo biosynthesis of TAG.
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http://dx.doi.org/10.1016/j.biortech.2016.09.025DOI Listing
November 2016

Magnesium aminoclay enhances lipid production of mixotrophic Chlorella sp. KR-1 while reducing bacterial populations.

Bioresour Technol 2016 Nov 12;219:608-613. Epub 2016 Aug 12.

Biomass and Waste Energy Laboratory, Korea Institute of Energy Research, Daejeon 34129, Republic of Korea. Electronic address:

Improving lipid productivity and preventing overgrowth of contaminating bacteria are critical issues relevant to the commercialization of the mixotrophic microalgae cultivation process. In this paper, we report the use of magnesium aminoclay (MgAC) nanoparticles for enhanced lipid production from oleaginous Chlorella sp. KR-1 with simultaneous control of KR-1-associated bacterial growth in mixotrophic cultures with glucose as the model substrate. Addition of 0.01-0.1g/L MgAC promoted microalgal biomass production better than the MgAC-less control, via differential biocidal effects on microalgal and bacterial cells (the latter being more sensitive to MgAC's bio-toxicity than the former). The inhibition effect of MgAC on co-existing bacteria was, as based on density-gradient-gel-electrophoresis (DGGE) analysis, largely dosage-dependent and species-specific. MgAC also, by inducing an oxidative stress environment, increased both the cell size and lipid content of KR-1, resulting in a considerable, ∼25% improvement of mixotrophic algal lipid productivity (to ∼410mgFAME/L/d) compared with the untreated control.
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http://dx.doi.org/10.1016/j.biortech.2016.08.034DOI Listing
November 2016

Advanced nanoporous TiO2 photocatalysts by hydrogen plasma for efficient solar-light photocatalytic application.

Sci Rep 2016 07 13;6:29683. Epub 2016 Jul 13.

Department of BioNano Technology, Gachon University, Gyeonggi-do 13120, Republic of Korea.

We report an effect involving hydrogen (H2)-plasma-treated nanoporous TiO2(H-TiO2) photocatalysts that improve photocatalytic performance under solar-light illumination. H-TiO2 photocatalysts were prepared by application of hydrogen plasma of assynthesized TiO2(a-TiO2) without annealing process. Compared with the a-TiO2, the H-TiO2 exhibited high anatase/brookite bicrystallinity and a porous structure. Our study demonstrated that H2 plasma is a simple strategy to fabricate H-TiO2 covering a large surface area that offers many active sites for the extension of the adsorption spectra from ultraviolet (UV) to visible range. Notably, the H-TiO2 showed strong ·OH free-radical generation on the TiO2 surface under both UV- and visible-light irradiation with a large responsive surface area, which enhanced photocatalytic efficiency. Under solar-light irradiation, the optimized H-TiO2 120(H2-plasma treatment time: 120 min) photocatalysts showed unprecedentedly excellent removal capability for phenol (Ph), reactive black 5(RB 5), rhodamine B (Rho B) and methylene blue (MB) - approximately four-times higher than those of the other photocatalysts (a-TiO2 and P25) - resulting in complete purification of the water. Such well-purified water (>90%) can utilize culturing of cervical cancer cells (HeLa), breast cancer cells (MCF-7), and keratinocyte cells (HaCaT) while showing minimal cytotoxicity. Significantly, H-TiO2 photocatalysts can be mass-produced and easily processed at room temperature. We believe this novel method can find important environmental and biomedical applications.
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http://dx.doi.org/10.1038/srep29683DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4942796PMC
July 2016

Lithographically Encrypted Inverse Opals for Anti-Counterfeiting Applications.

Small 2016 Jul 3;12(28):3819-26. Epub 2016 Jun 3.

Department of Chemical and Biomolecular Engineering (BK21+ Program), KAIST, Daejeon, 305-701, South Korea.

Colloidal photonic crystals possess inimitable optical properties of iridescent structural colors and unique spectral shape, which render them useful for security materials. This work reports a novel method to encrypt graphical and spectral codes in polymeric inverse opals to provide advanced security. To accomplish this, this study prepares lithographically featured micropatterns on the top surface of hydrophobic inverse opals, which serve as shadow masks against the surface modification of air cavities to achieve hydrophilicity. The resultant inverse opals allow rapid infiltration of aqueous solution into the hydrophilic cavities while retaining air in the hydrophobic cavities. Therefore, the structural color of inverse opals is regioselectively red-shifted, disclosing the encrypted graphical codes. The decoded inverse opals also deliver unique reflectance spectral codes originated from two distinct regions. The combinatorial code composed of graphical and optical codes is revealed only when the aqueous solution agreed in advance is used for decoding. In addition, the encrypted inverse opals are chemically stable, providing invariant codes with high reproducibility. In addition, high mechanical stability enables the transfer of the films onto any surfaces. This novel encryption technology will provide a new opportunity in a wide range of security applications.
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http://dx.doi.org/10.1002/smll.201601140DOI Listing
July 2016

Alginate microgels created by selective coalescence between core drops paired with an ultrathin shell.

J Mater Chem B 2016 May 20;4(19):3232-3238. Epub 2016 Apr 20.

Department of Chemical and Biomolecular Engineering, KAIST, Daejeon 34141, Korea.

We report a highly biocompatible and practical protocol to create alginate microgels for bioactive encapsulation. Double-emulsion drops composed of dual cores enclosed by an ultrathin shell are prepared in a capillary microfluidic device, which exhibit selective coalescence between the cores. When the cores are laden with alginate precursors and divalent ions, respectively, coalescence leads to the formation of alginate microgels in the fused core of double-emulsion drops. The microgel can be rapidly released into a continuous water phase by rupturing the liquid shell. This method neither involves any toxic chemical cues for gelation nor long-term exposure to oil, thereby providing highly biocompatible encapsulation.
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http://dx.doi.org/10.1039/c6tb00580bDOI Listing
May 2016

Efficient harvesting of wet blue-green microalgal biomass by two-aminoclay [AC]-mixture systems.

Bioresour Technol 2016 Jul 22;211:313-8. Epub 2016 Mar 22.

Department of BioNano Technology, Gachon University, 1342 Seongnamdaero, Sujeong-gu, Seongnam-si, Gyeonggi-do 13120, Republic of Korea. Electronic address:

Blue-green microalgal blooms have been caused concerns about environmental problems and human-health dangers. For removal of such cyanobacteria, many mechanical and chemical treatments have been trialled. Among various technologies, the flocculation-based harvesting (precipitation) method can be an alternative if the problem of the low yield of recovered biomass at low concentrations of cyanobacteria is solved. In the present study, it was utilized mixtures of magnesium aminoclay [MgAC] and cerium aminoclay [CeAC] with different particle sizes to harvest cyanobacteria feedstocks with ∼100% efficiency within 1h by ten-fold lower loading of ACs compared with single treatments of [MgAC] or [CeAC]. This success was owed to the compact networks of the different-sized-ACs mixture for efficient bridging between microalgal cells. In order to determine the usage potential of biomass harvested with AC, the mass was heat treated under the reduction condition. This system is expected to be profitably utilizable in adsorbents and catalysts.
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http://dx.doi.org/10.1016/j.biortech.2016.03.111DOI Listing
July 2016

Lipid extraction from microalgae cell using persulfate-based oxidation.

Bioresour Technol 2016 Jan 4;200:1073-5. Epub 2015 Nov 4.

Department of Civil and Environmental Engineering, KAIST, 373-1, Guseong-dong, Yuseong-gu, Daejeon 305-701, Republic of Korea. Electronic address:

In this study, persulfate, a solid-type oxidant, was adopted as a substitute for hydrogen peroxide in extracting lipid from microalgae biomass. Microalgae cells were concentrated at pH 3 and with 200mg/L of ferric chloride, conditions which can activate oxidants such as hydrogen peroxide and persulfate. At a persulfate concentration of 2mM and a reaction temperature of 90°C, exceedingly high extraction efficiency over 95% was obtained, which was higher than with 0.5% hydrogen peroxide at the same temperature. This result showed that persulfate is sufficiently powerful and incomparably cheap enough to replace the potent yet expensive oxidant. It appears that combining iron-based coagulation and persulfate-based lipid extraction is indeed a competitive approach that can possibly lighten the process burden for the microalgae-derived biodiesel production.
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http://dx.doi.org/10.1016/j.biortech.2015.10.106DOI Listing
January 2016

Regenerative Astaxanthin Extraction from a Single Microalgal (Haematococcus pluvialis) Cell Using a Gold Nano-Scalpel.

ACS Appl Mater Interfaces 2015 Oct 1;7(40):22702-8. Epub 2015 Oct 1.

Biomass and Waste Energy Laboratory, Korea Institute of Energy Research , Daejeon 34129, Korea.

Milking of microalgae, the process of reusing the biomass for continuous production of target compounds, can strikingly overcome the time and cost constraints associated with biorefinery. This process can significantly improve production efficiency of highly valuable chemicals, for example, astaxanthin (AXT) from Haematococcus pluvialis. Detailed understanding of the biological process of cell survival and AXT reaccumulation after extraction would be of great help for successful milking. Here we report extraction of AXT from a single cell of H. pluvialis through incision of the cell wall by a gold nanoscalpel (Au-NS), which allows single-cell analysis of wound healing and reaccumulation of AXT. Interestingly, upon the Au-NS incision, the cell could reaccumulate AXT at a rate two times faster than the control cells. Efficient extraction as well as minimal cellular damage, keeping cells alive, could be achieved with the optimized shape and dimensions of Au-NS: a well-defined sharp tip, thickness under 300 nm, and 1-3 μm of width. The demonstration of regenerative extraction of AXT at a single cell level hints toward the potential of a milking process for continuous recovery of target compounds from microalgae while keeping the cells alive.
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http://dx.doi.org/10.1021/acsami.5b07651DOI Listing
October 2015

Cell-wall disruption and lipid/astaxanthin extraction from microalgae: Chlorella and Haematococcus.

Bioresour Technol 2016 Jan 31;199:300-310. Epub 2015 Aug 31.

Biomass and Waste Energy Laboratory, Korea Institute of Energy Research, 152 Gajeong-ro, Yuseong-gu, Daejeon 305-343, Republic of Korea. Electronic address:

Recently, biofuels and nutraceuticals produced from microalgae have emerged as major interests, resulting in intensive research of the microalgal biorefinery process. In this paper, recent developments in cell-wall disruption and extraction methods are reviewed, focusing on lipid and astaxanthin production from the biotechnologically important microalgae Chlorella and Haematococcus, respectively. As a common, critical bottleneck for recovery of intracellular components such as lipid and astaxanthin from these microalgae, the composition and structure of rigid, thick cell-walls were analyzed. Various chemical, physical, physico-chemical, and biological methods applied for cell-wall breakage and lipid/astaxanthin extraction from Chlorella and Haematococcus are discussed in detail and compared based on efficiency, energy consumption, type and dosage of solvent, biomass concentration and status (wet/dried), toxicity, scalability, and synergistic combinations. This report could serve as a useful guide to the implementation of practical downstream processes for recovery of valuable products from microalgae including Chlorella and Haematococcus.
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http://dx.doi.org/10.1016/j.biortech.2015.08.107DOI Listing
January 2016