Consolidated bioprocessing of cellulose to itaconic acid by a co-culture of Trichoderma reesei and Ustilago maydis

Abstract

Background Itaconic acid is a bio-derived platform chemical with uses ranging from polymer synthesis to biofuel production. The efficient conversion of cellulosic waste streams into itaconic acid could thus enable the sustainable production of a variety of substitutes for fossil oil based products. However, the realization of such a process is currently hindered by an expensive conversion of cellulose into fermentable sugars. Here, we present the stepwise development of a fully consolidated bioprocess (CBP), which is capable of directly converting recalcitrant cellulose into itaconic acid without the need for separate cellulose hydrolysis including the application of commercial cellulases. The process is based on a synthetic microbial consortium of the cellulase producer Trichoderma reesei and the itaconic acid producing yeast Ustilago maydis. A method for process monitoring was developed to estimate cellulose consumption, itaconic acid formation as well as the actual itaconic acid production yield online during co-cultivation. Results The efficiency of the process was compared to a simultaneous saccharification and fermentation setup (SSF). Because of the additional substrate consumption of T. reesei in the CBP, the itaconic acid yield was significantly lower in the CBP than in the SSF. In order to increase yield and productivity of itaconic acid in the CBP, the population dynamics was manipulated by varying the inoculation delay between T. reesei and U. maydis. Surprisingly, neither inoculation delay nor inoculation density significantly affected the population development or the CBP performance. Instead, the substrate availability was the most important parameter. U. maydis was only able to grow and to produce itaconic acid when the cellulose concentration and thus, the sugar supply rate, was high. Finally, the metabolic processes during fed-batch CBP were analyzed in depth by online respiration measurements. Thereby, substrate availability was again identified as key factor also controlling itaconic acid yield. In summary, an itaconic acid titer of 34 g/L with a total productivity of up to 0.07 g/L/h and a yield of 0.16 g/g could be reached during fed-batch cultivation. Conclusion This study demonstrates the feasibility of consortium-based CBP for itaconic acid production and also lays the fundamentals for the development and improvement of similar microbial consortia for cellulose-based organic acid production.

An Optimized Ustilago maydis for Itaconic Acid Production at Maximal Theoretical Yield

“…maydis produces itaconate as one product from a potpourri of metabolites including organic acids such as malate, succinate, and (S)-2-hydroxyparaconate, polyols such as erythritol and mannitol, and different lipidic products including glycolipids and triglycerides [28][29][30][31][32][33]. It can also metabolize a range of renewable carbon sources, which besides sugar also include glycerol [34], galacturonic acid [35], cellulose [36], xylan [37], and pectin [38]. Although these features make U. maydis an attractive candidate for industrial applications [9,39,40], it also poses a drawback because often multiple products are produced simultaneously.…”

Current Progress in Production of Building-Block Organic Acids by Consolidated Bioprocessing of Lignocellulose

“…Itaconic Acid (IA) IA (methylenesuccinic acid) is a bio-based platform chemical with multiple applications that range from polymer synthesis to biofuel production [34]. In addition, immunomodulatory and antimicrobial activity of IA has been reported [143].…”

Challenges and Future Perspectives of Promising Biotechnologies for Lignocellulosic Biorefinery

“…T. reesei and Ustilago maydis can both grow in oxygen conditions at 30 • C. In this co-culturing system, T. reesei plays a role in lignocellulosic degradation, and U. maydis is responsible for itaconic acid production. The itaconic acid titer achieved 33.8 g/L from 120 g/L α-cellulose with fed-batch CBP strategy [107]. To further improve the adaptation between members of the co-culturing system, genetic engineering and adaptive evolution are adopted.…”