초록
<P><B>Background</B></P><P>Clostridial co-culture containing cellulolytic and solventogenic species is a potential consolidated bioprocessing (CBP) approach for producing biochemicals and biofuels from cellulosic biomass. It has been demonstrated that the rate of cellulose utilization in the co-culture of <I>Clostridium acetobutylicum</I> and <I>Clostridium cellulolyticum</I> is improved compared to the mono-culture of <I>C. cellulolyticum</I> (BL 5:119-124, 1983). However, the metabolic interactions in this co-culture are not well understood. To investigate the metabolic interactions in this co-culture we dynamically characterized the physiology and microbial composition using qPCR.</P><P><B>Results</B></P><P>The qPCR data suggested a higher growth rate of <I>C. cellulolyticum</I> in the co-culture compared to its mono-culture. Our results also showed that in contrast to the mono-culture of <I>C. cellulolyticum</I>, which did not show any cellulolytic activity under conditions similar to those of co-culture, the co-culture did show cellulolytic activity even superior to the <I>C. cellulolyticum</I> mono-culture at its optimal pH of 7.2. Moreover, experiments indicated that the co-culture cellulolytic activity depends on the concentration of <I>C. acetobutylicum</I> in the co-culture, as no cellulolytic activity was observed at low concentration of <I>C. acetobutylicum</I>, and thus confirming the essential role of <I>C. acetobutylicum</I> in improving <I>C. cellulolyticum</I> growth in the co-culture. Furthermore, butanol concentration of 350 mg/L was detected in the co-culture batch experiments.</P><P><B>Conclusion</B></P><P>These results suggest the presence of synergism between these two species, while <I>C. acetobutylicum</I> metabolic activity significantly improves the cellulolytic activity in the co-culture, and allows <I>C. cellulolyticum</I> to survive under harsh co-culture conditions, which do not allow <I>C. cellulolyticum</I> to grow and metabolize cellulose independently. It is likely that <I>C. acetobutylicum</I> improves the cellulolytic activity of <I>C. cellulolyticum</I> in the co-culture through exchange of metabolites such as pyruvate, enabling it to grow and metabolize cellulose under harsh co-culture conditions.</P>