Duk-Ki Kim

Isolation and characterization of a new mucoid-free Klebsiella pneumoniae strain for 2,3-butanediol production

The secretion of mucoid substances by Klebsiella pneumoniae , a natural 2,3-butanediol (2,3-BD) hyper-producer, hinders its application in large-scale fermentation because of pathogenicity, fermentation instability, and downstream difficulty. In this study, 14 K. pneumoniae strains were isolated from a waste water treatment plant and their 2,3-BD production efficiencies were assessed with the strain K. pneumoniae DSM2026. Among various strains isolated, K. pneumoniae GSC010 and GSC112 produced relatively large amounts of 2,3-BD compared to other isolates; and their 2,3-BD production was consistent with DSM2026. Meanwhile, mucoidic characteristics of GSC010 were more or less similar to DSM2026, which was observed by scanning electron microscope (SEM) as a characteristic intercalated thread anchored on the surface of the cells. However, no polysaccharide materials were found in a non-mucoid cell, GSC112. Fed-batch culture of GSC112 with continuous glucose feeding resulted in the production of 2,3-BD at 52.4 g/l with 2,3-BD yield and overall productivity of 0.27 g/g glucose and 0.52 g/l/h, respectively. These results strongly suggest that the newly isolated mucoid-free K. pneumoniae GSC112 has potential for industrial production of 2,3-BD. Keywords: 2,3-Butanediol, Klebsiella pneumoniae , isolation, capsular polysaccharides, scanning electron microscopy

Production of 2,3-butanediol by Klebsiella oxytoca from various sugars in microalgal hydrolysate

A new fermentation process using a mixed sugar medium is proposed in this study for 2,3‐butanediol (2,3‐BDO) production. The medium contained seven different monosugars known to be present in Nannochloropsis oceanica hydrolysate. The performance of each sugar when existing alone or together with glucose was evaluated. All the sugars except fucose were successfully metabolized for 2,3‐BDO production. A 2,3‐BDO yield of 0.31g/g was achieved with the mixed sugar medium, which was very close to that with the glucose‐only medium. However, the 2,3‐BDO productivity (0.28 g L−1 h−1) was found to be about 30% lower than that with glucose, implying, as expected, the existence of glucose repression on the uptake of other sugars. Strain development is in need to remove such negative effect of glucose for improved process efficiency. Fucose with the lowest uptake rate and no contribution to 2,3‐BDO production can be a high value‐added byproduct, once recovered and purified.

Development of a semi-continuous two-stage simultaneous saccharification and fermentation process for enhanced 2,3-butanediol production by Klebsiella oxytoca

Klebsiella oxytoca naturally produces a large amount of 2,3‐butanediol (2,3‐BD), a promising chemical with wide industrial applications, along with various by‐products. Previously, we have developed a metabolically engineered K. oxytoca ΔldhA ΔpflB strain to reduce the formation of by‐products. To improve 2,3‐BD productivity and examine the stability of K. oxytoca ΔldhA ΔpflB strain for industrial application, a semi‐continuous two‐stage simultaneous saccharification and fermentation (STSSF) process was developed. The STSSF with the K. oxytoca ΔldhA ΔpflB mutant using cassava as a carbon source could produce 108 ± 3·73 g(2,3‐BD) l−1 with a yield of 0·45 g(2,3‐BD) g(glucose)−1 and a productivity of 3·00 g(2,3‐BD)l−1 h−1. No apparent changes in the final titre, yield and productivity of 2,3‐BD were observed for up to 20 cycles of STSSF. Also, microbial contamination and spontaneous mutation of the host strain with potential detrimental effects on fermentation efficiency did not occur during the whole fermentation period. These results strongly underpin that the K. oxytoca ΔldhA ΔpflB mutant is stable and that the STSSF process is commercially exploitable.