Changsu Lee

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.

Growth temperature dependence on the formation of carbon-induced Ge quantum dots

Abstract Carbon has been exploited to form Ge quantum dots since it can provide effective nucleation sites. In this study, C-induced Ge quantum dots grown by solid source molecular beam epitaxy are investigated as a function of pre-deposited C coverage, overgrown Ge coverage, and substrate temperature using atomic force microscopy. The smallest quantum dots with a 300 A mean lateral diameter, a 50 A mean height, and an areal density of 3.0×10 10 cm −2 are obtained with 0.1 monolayer C pre-deposition and a 3 monolayer thick Ge overlayer. Growth temperature dependence for the Ge dot growth reveals that the dot density and size are abruptly changed by two orders of magnitude near 500°C. This is attributed to the difference in the temperature-dependent surface diffusivities of Ge and C adatoms on Si(100) substrate. The experimental results suggest that growth temperature plays a key role and should be kept below 500°C.

Effect of the ethylene precursor, 1-aminocyclopropane-1-carboxylic acid on different growth stages of Haematococcus pluvialis.

In this study, we explored the effects of ACC on other stages of H. pluvialis. Interestingly, even though ACC displayed a dose-dependent effect on astaxanthin production, it is evident that astaxanthin production could be facilitated whenever the cells were treated at the early red stage. The transcriptional levels of BKT, CHY, SOD, and CAT genes supported enhanced astaxanthin biosynthesis upon ACC treatment at the early red stage. The combinatorial synergistic effect of ACC and light intensity was also confirmed. Finally, two-step application of ACC at the vegetative phase to increase biomass production and at the early-red stage to promote astaxanthin biosynthesis was proposed to maximize the efficiency of ACC treatment.

Novel haloarchaeon Natrinema thermophila having the highest growth temperature among haloarchaea with a large genome size

Environmental temperature is one of the most important factors for the growth and survival of microorganisms. Here we describe a novel extremely halophilic archaeon (haloarchaea) designated as strain CBA1119T isolated from solar salt. Strain CBA1119T had the highest maximum and optimal growth temperatures (66 °C and 55 °C, respectively) and one of the largest genome sizes among haloarchaea (5.1 Mb). It also had the largest number of strain-specific pan-genome orthologous groups and unique pathways among members of the genus Natrinema in the class Halobacteria. A dendrogram based on the presence/absence of genes and a phylogenetic tree constructed based on OrthoANI values highlighted the particularities of strain CBA1119T as compared to other Natrinema species and other haloarchaea members. The large genome of strain CBA1119T may provide information on genes that confer tolerance to extreme environmental conditions, which may lead to the discovery of other thermophilic strains with potential applications in industrial biotechnology.

Salicibibacter kimchii gen. nov., sp. nov., a moderately halophilic and alkalitolerant bacterium in the family Bacillaceae, isolated from kimchi

A moderately halophilic and alkalitolerant bacterial strain NKC1-1T was isolated from commercial kimchi in Korea. Strain NKC1-1T was Gram-stain-positive, aerobic, rod-shaped, non-motile, and contained diaminopimelic acid-type murein. Cell growth was observed in a medium containing 0–25% (w/v) NaCl (optimal at 10% [w/v]), at 20–40°C (optimal at 37°C) and pH 6.5–10.0 (optimal at pH 9.0). The major isoprenoid quinone of the isolate was menaquinone-7, and the major polar lipids were phosphatidylglycerol and unidentified phospholipids. Cell membrane of the strain contained iso-C17:0 and anteiso-C15:0 as the major fatty acids. Its DNA G + C content was 45.2 mol%. Phylogenetic analysis indicated the strain to be most closely related to Geomicrobium halophilum with 92.7–92.9% 16S rRNA gene sequence similarity. Based on polyphasic taxonomic evaluation with phenotypic, phylogenetic, and chemotaxonomic analyses, the strain represents a novel species in a new genus, for which the name Salicibibacter kimchii gen. nov., sp. nov. is proposed (= CECT 9537T; KCCM 43276T).

Establishment of a new strategy against Microcystis bloom using newly isolated lytic and toxin-degrading bacteria

Unwanted, rapid increases in the algal populations of water systems cause harmful algal blooms, which have recently become a major environmental problem. The cyanobacterium Microcystis aeruginosa is the most prevalent bloom species and is responsible for the majority of blooms in freshwater environments. In this study, we attempted to develop an eco-friendly method to suppress M. aeruginosa bloom based on a biological control using bacteria newly isolated from the soil. In a screen for bacteria with strong lethal activity toward Microcystis, we isolated Bacillus sp. T4 and characterised its algicidal activity. Microcystis aeruginosa cells were killed via indirect attack by compound(s) secreted by T4 bacteria. ELISA revealed a dramatic increase in extracellular microcystins in M. aeruginosa cultures upon treatment with T4. Therefore, we screened for bacteria that could degrade these toxins, and three new isolates (R12, S42 and S65) were identified. Simultaneous application of both T4 as a lytic agent and R12 or S42 as toxin-degrading bacteria could eliminate both Microcystis cells and its problematic toxin. Our eco-friendly approach, based on the application of newly isolated bacteria, provides a novel method to control harmful algal blooms.

Role of jeotgal, a Korean traditional fermented fish sauce, in microbial dynamics and metabolite profiles during kimchi fermentation

We investigated the effects of jeotgal (fermented fish sauce) on kimchi fermentation, with or without saeu-jeot and myeolchi-jeot. Bacterial community analysis showed that Leuconostoc, Weissella, Lactobacillus, and Tetragenococcus were the dominant genera; however, their succession depended on the presence of jeotgal. Leuconostoc gasicomitatum was the dominant species in kimchi without jeotgal, whereas Weissella koreensis and Lactobacillus sakei were the dominant species in kimchi with myeolchi-jeot and saeu-jeot, respectively. Metabolite analysis, using 1H NMR, showed that the amounts of amino acids and gamma-aminobutyric acid (GABA) were higher in kimchi with jeotgal. Increases in acetate, lactate, and mannitol contents depended on fructose consumption and were more rapid in kimchi with jeotgal. Moreover, the consumption of various amino acids affected the increase in kimchi LAB. Thus, the role of jeotgal in kimchi fermentation was related to enhancement of taste, the amino acid source, and the increases in levels of functional metabolites.

Enhancement of microalga Haematococcus pluvialis growth and astaxanthin production by electrical treatment

In this study, we investigated the effects of electrical treatment on Haematococcus pluvialis growth. The slow growth of H. pluvialis is a major limitation for its mass production. We discovered that electrical treatment may promote the growth of H. pluvialis. To evaluate optimal growth-promoting conditions, the algal growth rate was investigated at various voltages. The optimum current was identified as 100 mA (voltage: 25 V). In comparison with the non-treated cells, those subjected to electrical treatment showed a 1.2 fold increase in cell density. Further experiments confirmed the direct impact of electrical treatment on the growth of H. pluvialis. The periodic application of electrical voltage resulted in a significant increase in the dry weight and astaxanthin production. The astaxanthin content in the periodic application of electrical treatment was 32.6 mg/L, which was a 10% increase compared to those in the non-treated controls. This strategy may serve as a novel approach to enhance H. pluvialis growth as well as astaxanthin production.

Genomic Analysis of Bacillus licheniformis CBA7126 Isolated from a Human Fecal Sample

Bacillus licheniformis is a Gram-positive, endospore-forming, saprophytic organism that occurs in plant and soil (Veith et al., 2004). A taxonomical approach shows that it is closely related to Bacillus subtilis (Lapidus et al., 2002; Xu and Côte, 2003; Rey et al., 2004). Generally, most bacilli are predominantly aerobic; however, B. licheniformis is a facultative anaerobe compared to other bacilli in ecological niches (Alexander, 1977). The commercial utility of the extracellular products of B. licheniformis makes this microorganism an economically interesting species (Kovács et al., 2009). For example, B. licheniformis is used industrially for manufacturing biochemicals, enzymes, antibiotics, and aminopeptidase. Several proteases such as α-amylase, penicillinase, pentosanase, cycloglucosyltransferase, β-mannanase, and certain pectinolytic enzymes are synthesized industrially using B. licheniformis (Rodríguez-Absi and Prescott, 1978; Rey et al., 2004). The proteases are used in the detergent industry and the amylases are utilized for starch hydrolysis, desizing of textiles, and sizing of paper (Erickson, 1976). In addition, certain strains are utilized to produce peptide antibiotics, specialty chemicals, and poly-γ-glutamic acid (Nierman and Maglott, 1989; Rey et al., 2004). The annotated genome sequence of B. licheniformis has been previously analyzed to assess the biotechnological importance of the organism (Veith et al., 2004). Since the first sequencing, the genomes of specific B. licheniformis strains have been sequenced to completely realize its industrial potential. In this study, genome sequencing of B. licheniformis CBA7126 isolated from a human fecal sample was performed to understand bacterial specificity. The genome sequence of CBA7126 revealed features such as stress response genes, antibiotic-resistance genes, and genes for resistance to toxic compounds, which are of considerable biotechnological value.

Generation of Reactive Oxygen Species via NOXa Is Important for Development and Pathogenicity of Mycosphaerella graminicola.

Abstract The ascomycete fungus Mycosphaerella graminicola (synonym Zymoseptoria tritici) is an important pathogen of wheat causing economically significant losses. The primary nutritional mode of this fungus is thought to be hemibiotrophic. This pathogenic lifestyle is associated with an early biotrophic stage of nutrient uptake followed by a necrotrophic stage aided possibly by production of a toxin or reactive oxygen species (ROS). In many other fungi, the genes CREA and AREA are important during the biotrophic stage of infection, while the NOXa gene product is important during necrotrophic growth. To test the hypothesis that these genes are important for pathogenicity of M. graminicola, we employed an over-expression strategy for the selected target genes CREA, AREA, and NOXa, which might function as regulators of nutrient acquisition or ROS generation. Increased expressions of CREA, AREA, and NOXa in M. graminicola were confirmed via quantitative real-time PCR and strains were subsequently assayed for pathogenicity. Among them, the NOXa over-expression strain, NO2, resulted in significantly increased virulence. Moreover, instead of the usual filamentous growth, we observed a predominance of yeast-like growth of NO2 which was correlated with ROS production. Our data indicate that ROS generation via NOXa is important to pathogenicity as well as development in M. graminicola.