Single reactor approach for platform chemical production from cellulose using a mixed culture
- Ein Reaktoransatz zur Produktion von Plattformchemikalien aus Cellulose mittels einer Mischkultur
Antonov, Elena; Büchs, Jochen (Thesis advisor); Agler-Rosenbaum, Miriam (Thesis advisor)
Aachen (2017, 2018)
Dissertation / PhD Thesis
Dissertation, RWTH Aachen University, 2017
As a first step for the set-up of a consolidated bioprocess for production of chemicals from cellulose, a method was developed to assess the digestibility of the applied substrate. The introduced method allowed the online evaluation of cellulose digestibility in complex and non-complex media by measuring the respiration activity of the cellulolytic fungus, Trichoderma reesei Rut-C30. Furthermore, the method could be applied to identify cellulase production enhancing compounds. Afterwards, a suitable cellulase-producing organism for a chosen model process should be identified. As a model process, the conversion of cellulose to the platform chemical itaconic acid by a mixed culture of a cellulolytic fungus with Aspergillus terreus as itaconic acid producer was evaluated. Five cellulase producers were analyzed by a newly developed freeze assay. It allows the assessment of the initial cellulase activity under process conditions by measuring the carbon release rate. The most promising candidates, T. reesei and Penicillium verruculosum were further characterized by monitoring their respiration activity during growth on cellulose. Both methods depicted that P. verruculosum is slightly better suitable than T reesei for the chosen model process. The presented method can be adapted to screen cellulose degrading organisms for various other applications. Finally, the production of two different platform chemicals - itaconic acid and gluconic acid - from cellulose was investigated. In a first proof of concept experiment itaconic acid could be produced from cellulose by a mixed culture of T. reesei and A. terreus by adding cellulolytic enzymes. A high enzyme concentration was needed to achieve a high glucose concentration in the fermentation broth, a prerequisite for itaconic acid production. Therefore, the conditions for enzyme production were optimized, causing the accumulation of itaconic acid production inhibiting substances. Next, the removal of these substances has to be evaluated. The production of gluconic acid was performed by T. reesei as cellulase producer and Gluconobacter oxydans as itaconic acid producer. However, the glucose release rate has to be further increased to allow gluconic acid production in the mixed culture approach.