So-Yeon Shin

Production of resveratrol from p-coumaric acid in recombinant Saccharomyces cerevisiae expressing 4-coumarate:coenzyme A ligase and stilbene synthase genes.

Resveratrol is a well-known polyphenol present in red wine and exerts antioxidative and anti-carcinogenic effects on the human body. To produce resveratrol in a food-grade yeast, the 4-coumarate:coenzyme A ligase gene (4CL1) from Arabidopsis thaliana and stilbene synthase gene (STS) from Arachis hypogaea were cloned and transformed into Saccharomyces cerevisiae W303-1A. The resveratrol produced was unglycosylated and secreted into the culture medium. A batch culture with 15.3mg/l p-coumaric acid used as precursor resulted in the production of 3.1mg/l resveratrol with 14.4 mol% yield. Deletion of the putative phenyl acrylic acid decarboxylase gene (PAD1) did not enhance resveratrol production.

Production of resveratrol from tyrosine in metabolically engineered Saccharomyces cerevisiae.

Resveratrol, a polyphenol compound found in grape skins, has been proposed to account for the beneficial effects of red wine against heart disease. To produce resveratrol in Saccharomyces cerevisiae, four heterologous genes were introduced: the phenylalanine ammonia lyase gene from Rhodosporidium toruloides, the cinnamic acid 4-hydroxylase and 4-coumarate:coenzyme A ligase genes both from Arabidopsis thaliana, and the stilbene synthase gene from Arachis hypogaea. When this recombinant yeast was cultivated by batch fermentation in YP medium containing 2% galactose, it produced 2.6 mg/L p-coumaric acid and 3.3 mg/L resveratrol. In order to increase the pool of malonyl-CoA, a key precursor in resveratrol biosynthesis, the acetyl-CoA carboxylase (ACC1) gene was additionally overexpressed in the yeast by replacing the native promoter of the ACC1 gene with the stronger GAL1 promoter and this resulted in enhanced production of resveratrol (4.3 mg/L). Furthermore, when tyrosine was supplemented in the medium, the concentration of resveratrol increased up to 5.8 mg/L. This result illustrates a possible strategy for developing metabolically engineered yeast strain for the economical production of resveratrol from cheap amino acids.

Production and solid-phase refolding of human glucagon-like peptide-1 using recombinant Escherichia coli.

Human glucagon-like peptide-1 (GLP-1), an incretin hormone with pharmaceutical potential in treating type 2 diabetes mellitus is known to be rapidly degraded when expressed in Escherichia coli. For the efficient production of the intact GLP-1 using a recombinant E. coli system, a fusion protein of GLP-1 was designed to be composed of the 6-lysine tag, ubiquitin and GLP-1 (K6UbGLP-1) in a row. A fed-batch fermentation of recombinant E. coli BL21(DE3)/pAPK6UbGLP-1 was carried out in a pH-stat feeding strategy and resulted in 11.3 g/L of K6UbGLP-1 as a form of inclusion body. Solid-phase refolding of K6UbGLP-1 inclusion body using a cation exchanger of the SP Sepharose FF led to a refolding yield over 90% even at 5.2 mg protein/mL resin. On-column cleavage of the refolded K6UbGLP-1 with ubiquitin-specific protease 1 gave an authentic form of GLP-1. Instrumental analyses using mass spectrometry and reverse-phase HPLC showed that the recombinant GLP-1 released from K6UbGLP-1 was identical to the standard GLP-1.

Production of Ginsenoside F2 by Using Lactococcus lactis with Enhanced Expression of β-Glucosidase Gene from Paenibacillus mucilaginosus

This study aimed to produce a pharmacologically active minor ginsenoside F2 from the major ginsenosides Rb1 and Rd by using a recombinant Lactococcus lactis strain expressing a heterologous β-glucosidase gene. The nucleotide sequence of the gene (BglPm) was derived from Paenibacillus mucilaginosus and synthesized after codon optimization, and the two genes (unoptimized and optimized) were expressed in L. lactis NZ9000. Codon optimization resulted in reduction of unfavorable codons by 50% and a considerable increase in the expression levels (total activities) of β-glucosidases (0.002 unit/mL, unoptimized; 0.022 unit/mL, optimized). The molecular weight of the enzyme was 52 kDa, and the purified forms of the enzymes could successfully convert Rb1 and Rd into F2. The permeabilized L. lactis expressing BglPm resulted in a high conversion yield (74%) of F2 from the ginseng extract. Utilization of this microbial cell to produce F2 may provide an alternative method to increase the health benefits of Panax ginseng.

Development of Bile Salt-Resistant Leuconostoc citreum by Expression of Bile Salt Hydrolase Gene.

Probiotic bacteria must have not only tolerance against bile salt but also no genes for antibiotic resistance. Leuconostoc citreum is a dominant lactic acid bacterium in various fermented foods, but it is not regarded as a probiotic because it lacks bile salt resistance. Therefore, we aimed to construct a bile salt-resistant L. citreum strain by transforming it with a bile salt hydrolase gene (bsh). We obtained the 1,001 bp bsh gene from the chromosomal DNA of Lactobacillus plantarum and subcloned it into the pCB4170 vector under a constitutive P710 promoter. The resulting vector, pCB4170BSH was transformed into L. citreum CB2567 by electroporation, and bile saltresistant transformants were selected. Upon incubation with glycodeoxycholic acid sodium salt (GDCA), the L. citreum transformants grew and formed colonies, successfully transcribed the bsh gene, and expressed the BSH enzyme. The recombinant strain grew in up to 0.3% (w/v) GDCA, conditions unsuitable for the host strain. In in vitro digestion conditions of 10 mM bile salt, the transformant was over 67.6% viable, whereas only 0.8% of the host strain survived.

Microbial Diversity of Commercial Makgeolli and Its Influence on the Organoleptic Characteristics of Korean Rice Sourdough, Jeung-Pyun

Sourdough is made by fermentation of dough by lactic acid bacteria (LAB) and yeast to improve bread properties like volume, flavor, and texture. A Korean traditional sourdough was made by fermenting rice flour with rice wine (makgeolli) and used to make sponge-like bread (jeung-pyun). The aim of this study was to investigate the microbial diversity of makgeolli products and their influence on the organoleptic quality of jeung-pyun. Three commercial makgeolli were tested for jeung-pyun production, with each product exhibiting varied dough swelling rates and organoleptic qualities, and among them, J-product was ranked highest in texture and taste. Microbial analysis of the three makgeolli also showed a big difference in their population and diversity. J-product had the highest LAB and yeast counts, and the predominant species were Lactobacillus casei, Lactobacillus brevis, Leuconostoc pseudomenteroides, and Saccharomyces cerevisiae. Using J-product, sourdough was fermented at 25°C, 30°C, and 35°C, and the microbial growth in and textural properties of jeung-pyun were examined by instrumental and sensory tests. At high temperature (35°C), the rates of dough swelling and acidification were fast due to rapid microbial growth mainly caused by LAB, resulting in a short leavening time and soft and sour jeung-pyun. Sensory tests showed consumer preference for the soft and mild-sour jeung-pyun. This study shows that LAB in makgeolli play key roles in production of jeung-pyun, influencing the textural and sensory properties. For the production of high-quality jeung-pyun, development of LAB starters with high gas productivity and low acidity and establishment of an optimal fermentation procedure for rice dough are necessary.