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

Abstract

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.

Hydrolysis of Lipid‐Extracted Chlorella vulgaris by Simultaneous Use of Solid and Liquid Acids

“…Overall, sugar consumption was slower in cells grown on the hydrolysate than in cells grown on the model solution. Carbon catabolite repression (CCR), which is universally observed in this microorganism, was confirmed. Sugars, except for glucose, decreased in concentration after consumption of glucose in both media.…”

“…This microorganism was purchased from the Korean Collection for Type Cultures and was precultivated on a shaker in a glucose medium at 37°C at pH 5.5. The glucose medium included (g/L): glucose, 9; yeast extract, 5; KH 2 PO 4 , 6.8; K 2 HPO 4 , 8.7; (NH 4 ) 2 SO 4 , 6; MgSO 4 , 0.25; and a trace metal solution 2% (v/v) with (g/L): FeSO 4 ·7H 2 O, 2.5; MnSO 4 ·H 2 O, 0.05; ZnSO 4 , 0.05; and CaCl 2 ·2H 2 O, 0.05 . The pre‐culture medium was added to the main culture medium and the hydrolysate of C. vulgaris at a ratio of 1:99, when the optical density at 600 nm of pre‐culture medium reached to 4.0.…”

“…In dealing with multisugar medium like microalgal hydrolysate, it is important to adopt microbial strains with very wide substrate specificity. For example, Klebsiella oxytoca can utilize all of the above mentioned eight sugars to produce 2,3‐butanediol (2,3‐BDO) …”

Engineering of Klebsiella oxytoca for production of 2,3‐butanediol using mixed sugars derived from lignocellulosic hydrolysates

“…Previously, we analyzed sugar utilization ability in K. oxytoca , and found that among four major sugars, namely xylose, glucose, galactose, and mannose, xylose utilization ability was much lower than that of the other sugars (Kim et al, ). Therefore, to elevate mixed sugar utilization ability, we focused on engineering xylose utilization ability.…”

“…However, we found the typical CCR phenomena was still observed when CHA006 was cultivated in the media containing glucose with other sugars. CCR by preferable glucose cause the reduction of overall sugar uptake in the cultivation, which is the most important issue in the utilization of multiple sugars (Kim et al, ). By the engineering (deletion or modification) of key components such as phosphoenolpyruvate‐dependent phosphotransferase system (PTS Glc ), CCR could be eliminated, and glucose and other sugars were utilized simultaneously (Ji, Nie, et al, ; Park et al, ).…”