Da-Hye Yi

Overexpression of succinyl‐CoA synthase for poly (3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) production in engineered Escherichia coli BL21(DE3)

This study aims to increase the 3‐hydroxyvalerate (3HV) fraction in poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) [P(HB‐co‐HV)] using succinyl‐CoA synthase.

Exopolysaccharide from psychrotrophic Arctic glacier soil bacterium Flavobacterium sp. ASB 3-3 and its potential applications

A novel exopolysaccharide (EPS) producing psychrotrophic bacterium Flavobacterium sp. ASB 3-3 was isolated from Arctic glacier soil and identified. The optimum fermentation conditions for EPS production were an initial medium pH of 7.2 and an initial inoculum size of 5% (v/v). The maximum yield of EPS (7.25 ± 0.26 g L−1) was obtained after cultivation at 25 °C for 120 h with glycerol as the sole carbon source. The EPS was purified and its structural characteristics were analyzed by 1H and 13C NMR. The predominant repeating units of this EPS are (α, β) D-glucose and D-galactose and it is different from the structure of EPSs produced by other Arctic and Antarctic bacteria, which have mannose units. In addition, EPS has demonstrated a comparable emulsifying property than SDS and flocculating properties with kaolinite, suggesting their potential applications in various industries. The EPS also significantly improved the tolerance of Flavobacterium sp. and Escherichia coli from freeze–thaw cycles, suggesting that it might be used to survive in polar regions and it can have possible usage as microbial cryoprotectants.

Sensitive change of iso-branched fatty acid (iso-15:0) in Bacillus pumilus PAMC 23174 in response to environmental changes

In this study, the environmental adaptive metabolic processes were investigated using a psychrotrophic polar bacterium Bacillus pumilus PAMC 23174 in response to various temperatures and nutrients, especially in regard to the synthesis of fatty acids. Fatty acid methyl ester analysis was performed using gas chromatography–mass spectrometry and we found that a sensitive changes in iso-branched fatty acid (iso-15:0) synthesis occurred when adjusting the nutritional ratio of branched chain fatty acids (anteiso/iso) with different temperatures, resulting in a change in the balance of anteiso- and iso-form fatty acids. We also observed that this Arctic bacterium preferred amino acid leucine for the synthesis of fatty acids. The increased and decreased synthesis of iso-form fatty acids in response to different temperatures and leucine preference, changes the fatty acid ratio in bacteria, which further affects the membrane fluidity and it is also directly correlated with survival of bacteria in an extreme environment. Hence, this study suggests that B. pumilus PAMC 23174 is a potential model organism for the analysis of the unique ecological adaptations of polar bacteria in changing and the extreme environments.

Increased Vulnerability to Physical Stress by Inactivation of NdgR in Streptomyces coelicolor

The antibiotic production and spore formation process in Streptomyces coelicolor need complex decision making processes by several regulatory units. These regulatory units are involved in both primary and secondary metabolism. As a result, most regulators have several functions, and those are worthwhile themes to study about different functions of a known regulator. In this study, a deletion mutant of ndgR, which encodes the nitrogen-dependent growth regulator, was examined by the cell viability test, TEM, and growth in N-acetylglucosamine/asparagine (GlcNAc/Asn) liquid medium. The results of the study show that NdgR is also involved in the structure of the cell membrane affecting survival under physical shocks. Deletion of ndgR leads to abnormal cell membrane resulting in the vulnerable cells to physical stress caused by shaking with beads in liquid culture condition. This empirical observation is the first meaningful explanation to why ndgR mutant could not grow well in a liquid minimal medium due to the defect of N-acetylglucosamine (GlcNAc) utilization and phospholipid synthesis.