초록
<P>Product inhibition by butanol and acetone is a known drawback in acetone-butanol-ethanol (ABE) fermentation. Extractive fermentation improves butanol production by several ABE-producing <I>Clostridium</I> spp., but only low volume ratios (<4) of extractant to broth (<I>V</I> <SUB>e</SUB>/<I>V</I> <SUB>b</SUB>) have been studied. Here, a novel extractive fermentation process was developed using <I>Clostridium saccharoperbutylacetonicum</I> N1-4 and a large <I>V</I> <SUB>e</SUB> <I>/V</I> <SUB>b</SUB> ratio. A mixture of oleyl alcohol-tributyrin (1:1 (v/v)) yielded high distribution coefficients for both butanol (3.14) and acetone (0.660). Although a fed-batch culture using free cells and the oleyl alcohol-tributyrin mixture at a <I>V</I> <SUB>e</SUB> <I>/V</I> <SUB>b</SUB> ratio of 5 had a lag phase of >24 h, it produced a higher concentration of total butanol (i.e., butanol produced in all the phases per broth volume used) of 24.2 g/L-broth after 96 h compared with 14.4 g/L-broth at a <I>V</I> <SUB>e</SUB> <I>/V</I> <SUB>b</SUB> ratio of 1, resulting in a low butanol concentration in the aqueous phase. The use of cells immobilized with calcium alginate beads shortened the lag phase to <12 h. Butanol production was achieved not only in a 3-phase mode (extractant, beads, and tryptone-yeast extract-acetate (TYA) medium) but also in a 2-phase mode (extractant and beads containing TYA medium, without an aqueous phase) at a <I>V</I> <SUB>e</SUB> <I>/V</I> <SUB>b</SUB> ratio of 5, resulting butanol concentrations of 30.9 g/L-broth and 27.7 g/L-broth, respectively. The 3-phases fed-batch extractive fermentation at a <I>V</I> <SUB>e</SUB> <I>/V</I> <SUB>b</SUB> ratio of 10 showed a better performance compared with published reports: a total butanol concentration of 64.6 g/L-broth and a butanol yield to consumed sugar of 0.378 C-mol/C-mol.</P> <P><B>Highlights</B></P> <P> <UL> <LI> New extractant mixture led to simultaneous extraction of butanol and acetone. </LI> <LI> Large extractant volume maintained lower butanol concentration in media. </LI> <LI> Extractive fermentation with immobilization succeeded using the minimized volume of media solution. </LI> <LI> Large volume ratio of extractant to broth resulted in high total butanol concentration. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>