• Microbiology and Biotechnology Letters
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• v.36 no.2
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• pp.158-164
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• 2008

The fusants which contain starch utilizing ability and alcohol fermenting ability were developed by protoplast fusion of Saccharomyces cerevisiae KOY-1 and Saccharomyces diastaticus KCTC 1804. Sacharomyces cerevisiae KH-12 was obtained by haploid induction from Saccharomyces cerevisiae KOY-1. The auxotropic mutants of yeast were obtained by using an ethylmethane sulfonate (EMS). The frequency of protoplast formation in Saccharomyces cerevisiae KOY-1 $(Met^-)$ and Saccharomyces diastaticus KCTC 1804 $(Trp^-)$ were 90.5% and 97.7%, respectively. The frequency of fusant formation was $1.79{\times}10^{-4 }$ for the regenerated protoplast and the 1,000 fusants were obtained. Fusant FA 776 was selected as a potential yeast which contain an alcohol fermenting ability in the starch medium. The genetic stability was 4.64% for 10 passages of generation. Fusant FA 776 produced 13mg/ml of alcohol in 24% starch medium and showed 1.86-fold higher alcohol fermenting ability than Saccharomyces diastaticus KCTC 1804.

• Korean Journal of Microbiology
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• v.37 no.2
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• pp.170-175
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• 2001

In order to produce xylitol with high yield, experiments were carried out to develope xylitol dehydrogenase(XDH) defective mutant from P. stipitis and to investigate the xylitol fermentation characteristics of mutant strain. After treatment of P. stipitis with EMS, mutant PXM-4 was selected based on te XDH activity and xylitol production capability. Among the tested cosubstrates, galactose was selected as an adequate cosub-strate on xylitol production of mutant PXM-4. But with the increase in the concentration of galactose in the medium, xylitol production was decreased because the transport of xylose into cell was inhibited by galactose. The optimal concentration of galactose for the production of xylitol using 20 g/ι xylose was 20 g/ι Under this condition, maximum concentration of xylitol and yield were 14.4 g/ι and 97%, respectively. In order to prevent the inhibitory effect of xylose transport by galactose, galactose was fed with low concentration and the concentration of xylitol produced was increased up to 25 g/ι.

• KSBB Journal
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• v.15 no.6
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• pp.566-572
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• 2000

Experimental studies were carried out to develop an osmotolerant mutant of Candida magnoliae JH and to determine the optimum concentrations of carbon and nitrogen sources to improve erythritol yield and productivity. Mutants of C. magnoliae JH were prepared by treatment with ethylmethane sulfonate, and osmotolerant mutants were isolated from the agar plate colonies containing 2.5 M KCI. Among the mutants isolated, one mutant M26 was finally selected based on erythritol yield and productivity. In shake flask culture, glucose proved to be the best carbon source and the optimum yeast extract concentration was 5 g/L based on 100 g/L glucose. The erythritol yield and productivity of mutant M26 were greater than wild type in 100 g/L glucose medium. in the fermentation experiments, erythritol production increased with increased glucose concentration, up to a limit of 250 g/L. The maximum concentration of erythritol achieved 127.5 g/L, and the yield and productivity of erythritol production were 51.0% and 0.63 g/L-h, respectively.

• Microbiology and Biotechnology Letters
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• v.48 no.3
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• pp.344-357
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• 2020

Strain improvement and bioprocess development were undertaken to enhance hyaluronic acid(HA) production by Streptococcus zooepidemicus cells. Using a high-yielding mutant strain, statistical medium optimization was carried out in shake flask cultures, resulting in 52% increase in HA production (5.38 g/l) at the optimal medium composition relative to the parallel control cultures. For sufficient supply of dissolved oxygen (DO), which turned out to be crucial for enhanced production of HA, agitation system and speed were intensively investigated in 5 L bioreactor cultures. Increase in oxygen mass transfer coefficient (k_La) through increment of agitation speed (rpm) and 35% expansion of diameter of the newly-designed impellers showed significantly positive effects on HA production. By installing an expanded Rushton-turbine impeller for efficient break-down of sparged air, and an extended marine impeller above the Rushton-turbine impeller for efficient mixing of the air-born viscous fermentation broth, maximum amount of HA (9.79 g/l) was obtained at 450 rpm, 1.8 times higher level than that of the corresponding flask culture. Subsequently, the possibility of bioprocess scale-up to a 50 L bioreactor was investigated. Despite almost identical maximum HA production (9.11 vs 9.25 g/l), the average HA volumetric productivity (r_p) of the 50 L culture turned out only 74% compared to the corresponding 5 L culture during the exponential phase, possibly caused by shear damages imposed on the producing cells at the high stirring in the 50 L culture. The scale-up process could be successfully achieved if a scale-up criterion of constant oxygen mass transfer coefficient (k_La) is applied to the 50 L pilot-scale bioreactor system.