Microbial systems for conversion of syngas to biobased products

Abstract

Synthesis gas, a mixture of CO, H2, and CO2, can be created via gasification of any carbohydrate material. Fermentation of syngas by carboxydotrophic microbes allows for it to be converted into interesting bio-chemicals. Organisms involved in the fermentation of syngas use the CO or H2 in the gas as electron donor, fixating CO2 into the final end products. Currently acetate and ethanol are relatively well established products from syngas fermentation and there is interest to broaden the scope towards production of more complex products. However, genetic engineering of carboxydotrophic organisms and the knowledge of their metabolism is rather limited, making it difficult to create strains producing these products. A possible way to broaden the scope of products is via co-cultivation of microbes which can make use of each others products. We established a co-cultivation of Clostridium autoethanogenum, a well-known carboxydotrophic acetogen, together with Clostridium kluyveri, a well characterized organism employing the reverse -oxidation pathway. C. autoethanogenum uses the syngas to produce a mixture of acetate and ethanol. C. kluyveri subsequently uses these products to perform chain elongation. This results in a co-culture producing a mixture of C4 and C6 acids and alcohols using carbon monoxide as a sole substrate. This co-culture poses an interesting way for production of more complex and valuable products from syngas. Basic characterization of these co-cultures has been done and currently the research focus lies on how the species interact with each other and how environmental factors influence their production patterns and metabolism.