17-25: Development of a symbiotic co-culture for ethanol production from cellulose

Implementation of consolidated bioprocessing of lignocellulosic materials for ethanol production is limited by, among other factors, the lack of a suitable organism to complete the required hydrolysis and fermentation steps. As an alternative to single culture bioprocessing, mixed cultures represent a potential solution to achieve the appropriate combination of metabolic and hydrolytic properties. However, the stability of mixed consortia and lack of simplistic bioprocessing are often cited as inhibitors of this type of approach.  This work is focused on development of a symbiotic co-culture of the cellulolytic mesophile, Clostridium phytofermentans, and a cellodextrin fermenting yeast, Candida molischiana, for direct ethanol production from cellulose. This symbiosis results in a stable system that behaves as if it were a mono-culture in that the organisms are metabolically linked to one another for successful proliferation. Cooperation is induced through diffusion of oxygen into culture media which acts to inhibit the growth of the obligate anaerobe, C. phytofermentans. When provided a soluble carbon source from C. phytofermentans hydrolysis, C. molischiana metabolizes the oxygen relieving the inhibitory effect. Under static, aerobic conditions the co-culture breaks down filter paper while mono-cultures are unable to do so. Co-culture stability, population dynamics, reactor design and recent progress in fermentation capabilities will be discussed.