• Journal of Microbiology and Biotechnology
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• v.25 no.2
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• pp.238-246
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• 2015

A unicellular red microalga was isolated from environmental freshwater in Korea, and its morphological, molecular, and biochemical properties were characterized. Morphological analysis revealed that the isolate was a unicellular biflagellated green microalga that formed a non-motile, thick-walled palmelloid or red aplanospore. To determine the taxonomical position of the isolate, its 18S rRNA and rbcL genes were sequenced and phylogenetic analysis was performed. We found that the isolate was clustered together with other related Haematococcus strains showing differences in the rbcL gene. Therefore, the isolated microalga was classified into the genus Haematococcus, and finally designated Haematococcus sp. KORDI03. The microalga could be cultivated in various culture media under a broad range of pH and temperature conditions. Compositions of the microalgal cellular components were analyzed, and its protein, carbohydrate, and lipid compositions were estimated to be 21.1 ± 0.2%, 48.8 ± 1.8%, and 22.2 ± 0.9%, respectively. In addition, D-glucose and D-mannose were the dominant monosaccharides in the isolate, and its amino acids were composed mainly of aspartic acid, glutamic acid, alanine, and leucine. Moreover, several polyunsaturated fatty acids accounted for about 80% of the total fatty acids in Haematococcus sp. KORDI03, and the astaxanthin content in the red aplanospores was estimated to be 1.8% of the dry cell weight. To the best of our knowledge, this is the first report of an Haematococcus sp. isolated from Korea, which may be used for bioresource production in the microalgal industry.

• Korean Chemical Engineering Research
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• v.52 no.1
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• pp.88-91
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• 2014

In this study, oil as a source of biodiesel from Nannochloropsis oceanica was extracted using organic solvent. The oil extraction yield and efficiency from dry and wet microalgae were investigated. The initial fatty acids content of the N. oceanica was 317.8 mg/g cell showing a high oil content over 30%. The yield from dry microalgae was higher than that from wet microalgae due to the inhibition of water. The yield by chloroform-methanol was the highest and the yield by hexane was the lowest. However, the total fatty acids contents with the chloroform-methanol were 678.7 and 778.2 mg/g oil under dry and wet conditions, respectively. The high oil extraction yield by chloroform-methanol reflected the fact that the extracted oil contained a high level of impurity. The hexane-methanol extraction from dry N. oceanica showed high oil extraction efficiency, 82.6%. The chloroform-methanol extraction under wet condition also showed high efficiency, 88.0%. While the hexane-methanol extraction from dry microalgae is desirable under low drying cost, the chloroform-methanol extraction from wet microalgae is desirable under high drying cost.

• The Korean Journal of Malacology
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• v.31 no.1
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• pp.35-41
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• 2015

In order to investigate the live food value of microalgae for efficacious rearing of larvae and spats of bivalve, we studied growth rates of four microalgal species (Isochrysis galbana, Pavlova lutheri, Chaetoceros simplex, Tetraselmis tetrathele) cultured in different environmental conditions. These include changes in temperatures (20, 25, 30 and $35^{\circ}C$), salinities (20, 25, 30 and 33 psu) and light intensities (60, 100 and $140{\mu}mol\;m^{-2}s^{-1}$). The growth rate of I. galbana was faster at $25^{\circ}C$ than that of $20^{\circ}C$. At $25^{\circ}C$ the highest growth rate of I. galbana was observed at 33 psu (0.413) and the lowest at 20 psu (0.368) in 10 days of culture (P < 0.05). The growth rate of I. galbana was lower at 25 psu (0.383) than that of 30 psu and higher than that of 20 psu (P < 0.05). Similar temperature and salinity-dependent changes were also found in P. lutheri and T. tetrathele. C. simplex showed faster growth rate at $30^{\circ}C$ than that of $25^{\circ}C$. The highest growth rate of C. simplex was observed at 33 psu (0.428) and the lowest at 20 psu (0.389) in 10 days of culture (P < 0.05). Upon exposure to the light with different intensities, all four microalgal species showed a significantly faster growth rate at $140{\mu}mol\;m^{-2}s^{-1}$ than at $100{\mu}mol\;m^{-2}s^{-1}$ (P < 0.05).

• Biotechnology and Bioprocess Engineering:BBE
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• v.8 no.6
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• pp.349-353
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• 2003

The physiological characteristics of cultures of very high cell mass (e.g. 10g cell mass/L), termed“ultrahigh cell density cultures”is reviewed. A close relationship was found between the length of the optical path (OP) in flat-plate reactors and the optimal cell density of the culture as well as its areal (g m$\^$-2/ day$\^$-1/) productivity. Cell-growth inhibition (GI) unfolds as culture density surpasses a certain threshold. If it is constantly relieved, a 1.0cm OP reactor could produce ca. 50% more than reactors with longer OP, e.g. 5 or 10cm. This unique effect, discovered by Hu et al. [3], is explained in terms of the relationships between the frequency of the light-dark cycle (L-D cycle), cells undergo in their travel between the light and dark volumes in the reactor, and the turnover time of the photosynthetic center (PC). In long OP reactors (5cm and above) the L-D cycle time may be orders of magnitude longer than the PC turnover time, resulting in a light regime in which the cells are exposed along the L-D cycle, to long, wasteful dark periods. In contrast, in reactors with an OP of ca. 1.0 cm, the L-D cycle frequency approaches the PC turnover time resulting in a significant reduction of the wasteful dark exposure time, thereby inducing a surge in photosynthetic efficiency. Presently, the major difficulty in mass cultivation of ultrahigh-density culture (UHDC) concerns cell growth inhibition in the culture, the exact nature of which is awaiting detailed investigation.

• Journal of Environmental Science International
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• v.21 no.7
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• pp.779-785
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• 2012

Several tests and experimental work have been done for identifying the best growth conditions and accumulated amount of lipid moiety in B. braunii, a microalga(UTEX 572) in terms of media composition. The specific growth rate was found to be the highest at 0.15 g/L-day when the phosphorus concentration was doubled with the other ingredients at the normal level. Experiments for varied media compositions revealed that the accumulation of lipid was the highest at 48% (dry cell weight based) in the nitrogen deficient medium and its corresponding specific growth rate was comparative to that in the normal BG 11 medium. In the bubble column experiments, carbon dioxide containing air produced four times more cell mass than air only. Light and glucose addition also enhanced cell mass with maximum, 1.8 g/L and accordingly 42% of lipid composition, which turned out to be a better strategy for higher lipid-producing microalgal culture.

• ALGAE
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• v.34 no.4
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• pp.267-275
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• 2019

Three new species of the genus Micractinium were collected from five localities on the South Shetland Islands in maritime Antarctica, and their morphological and molecular characteristics were investigated. The vegetative cells are spherical to ellipsoidal and a single chloroplast is parietal with a pyrenoid. Because of their simple morphology, no conspicuous morphological characters of new species were recognized under light microscopy. However, molecular phylogenetic relationships were inferred from the concatenated small subunit rDNA, and internal transcribed spacer (ITS) sequence data indicated that the Antarctic microalgal strains are strongly allied to the well-supported genus Micractinium, including M. pusillum, the type species of the genus, and three other species in the genus. The secondary structure of ITS2 and compensatory base changes were used to identify and describe six Antarctic Micractinium strains. Based on their morphological and molecular characteristics, we characterized three new species of Micractinium: M. simplicissimum sp. nov., M. singularis sp. nov., and M. variabile sp. nov.

• Clean Technology
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• v.21 no.2
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• pp.90-95
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• 2015

Digital microfluidic electroporation system was used for the transformation of microalgae and we have obtained higher transformation efficiency and viability than that of conventional method. Key parameters of electroporation such as pulse voltage, number, and duration time were systematically investigated for two different microalgal strains with and without cell wall. We have found that cell wall does not always have negative effects on the gene transformation of microalgae. Parallel processing of proposed digital microfluidic electroporation was demonstrated together with on chip culture of microalgae.

• 한국생물공학회:학술대회논문집
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• 2000.04a
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• pp.189-192
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• 2000

The objective of this study was to investigate the effect of high content of light-absorbing pigments on overall photosynthetic efficiency in high density microalgal cultures. The light harvesting complex II (LHC II) regulating gene of Rhodobacter sphaeroides, photosynthetic purple bacterium, was removed to construct a mutant strain that had less pigment content. The mutant and wild type strains were cultured under various light intensity by adjusting the distance from the light source. The productivity of the mutant strain was higher at high light intensity (over 118 ${\mu}E/m^2/s$) compared with one of the wild type , and was lower at low light intensity (34 ${\mu}E/m^2/s$). Especially, the concentration of LHC II mutant strain was 56% higher at 118 ${\mu}E/m^2/s$. The reduction of per cell pigment contents in the mutant strain lessened the degree of the mutual shading and thus enhanced the overall photosynthetic efficiency.

• KSBB Journal
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• v.19 no.4
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• pp.257-262
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• 2004

Recently, there is a growing interest in microalgae and the use of microalgae focused on the production of various high value metabolite used in food, pharmaceuticals and cosmetics. The key limiting factor in high density algal cultivation is the light and algal growth is defined by light intensity and light penetration depth into the culture medium. The effect of light with various light paths, S/V ratios, light intensities, and 50% duty cycle on the growth of microalgae was examined to enhance microalgal biomass productivity and photosynthetic efficiency. We confirmed that the utilization of efficient light energy was obtained from 4 cm of diameter, 57.6% of S/V ratio, 62 ${\mu}$mol/㎡/s of light intensity.

• ALGAE
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• v.22 no.4
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• pp.261-271
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• 2007

The variations of species compositions, standing crops and seasonal succession of phytoplanktons including Cyanophyceae, Chlorophyceae and Bacillariophyceae were investigated with physico-chemical elements of water to clarify the causes of water bloom according to the water depth in the Lake Unmun. The increased amounts of turbidity, T-N, T-P and SS originated from heavy rain and typhoon in the middle of June provoked to produce phytoplanktons. In July and August, the dominant species was Peridinium sp., while the subdominant species was Microcystis aeruginosa. In October, Aulacoseira distans was dominant and Asterionella formosa was subdominant. During the period of water shortage, the concentrated pollutants caused the decrease of precipitation, the long stagnation time of water body and the mixed pollutants by upwelling as decreasing water temperature could accelerate the water bloom. The preventives to decrease microalgal generation should be controled by the stagnation time of water body by increasing outflow to intercept water bloom such as ulacoseira sp. in October as well as summer.