Increase of xylitol productivity by cell-recycle fermentation of Candida tropicalis using submerged membrane bioreactor.
Candida tropicalis, an osmophilic strain isolated from honeycomb, produced xylitol at a maximal volumetric productivity of 3.5 g l(-1) h(-1) from an initial xylose concentration of 200 g l(-1). Even at a very high xylose concentration, e.g., 350 g l(-1), this strain produced xylitol at a moderate rate of 2.07 g l(-1) h(-1). In a fed-batch fermentation of xylose and glucose, 260 g l(-1) xylose was added, and the xylitol production was 234 g l(-1) for 48 h, corresponding to a rate of 4.88 g l(-1) h(-1). To increase xylitol productivity, cells were recycled in a submerged membrane bioreactor with suction pressure and air sparging. For each recycle round in cell-recycle fermentation, the average concentration of xylitol produced, fermentation time, volumetric productivity, and product yield were 180 g l(-1), 19.5 h, 8.5 g l(-1) h(-1), and 85%, respectively. When cell-recycle fermentation was started with the cell mass concentrated twofold after batch fermentation and performed for 10 recycle rounds, we achieved a very high productivity of 12 g l(-1) h(-1). The productivity and total amount of xylitol in cell-recycle fermentation were 3.4- and 11.0-fold higher than those in batch fermentation, respectively.
Kwon
Soun-Gyu
SG
Department of Bioscience and Biotechnology, Sejong University, 98 Gunja-dong, Gwangin-gu, Seoul 143-747, Korea.
Park
Seung-Won
SW
Oh
Deok-Kun
DK
D019149:Bioreactors / Q000382:microbiology*; D041022:Candida tropicalis / Q000378:metabolism*; D005285:Fermentation; D007101:Immersion; D007218:Industrial Microbiology / Q000379:methods*; D008566:Membranes / Q000737:chemistry; D014993:Xylitol / Q000096:biosynthesis*; D014994:Xylose / Q000378:metabolism
D014994:Xylose; D014993:Xylitol