In situ adsorption of itaconic acid from fermentations of Ustilago cynodontis improves bioprocess efficiency

BACKGROUND

Reducing the costs of biorefinery processes is a crucial step in replacing petrochemical products by sustainable, biotechnological alternatives. Substrate costs and downstream processing present large potential for improvement of cost efficiency. The implementation of in situ adsorption as an energy-efficient product recovery method can reduce costs in both areas. While selective product separation is possible at ambient conditions, yield-limiting effects, as for example product inhibition, can be reduced in an integrated process.

RESULTS

An in situ adsorption process was integrated into the production of itaconic acid with Ustilago cynodontis IAmax, as an example of a promising biorefinery process. A suitable feed strategy was developed to enable efficient production and selective recovery of itaconic acid by maintaining optimal glucose concentrations. Online monitoring via Raman spectroscopy was implemented to enable a first process control and understand the interactions of metabolites with the adsorbent. In the final, integrated bioprocess, yield, titre, and space-time yield of the fermentation process were increased to values of 0.41 gIA/gGlucose, 126.5 gIA/L and 0.52 gIA/L/h. This corresponds to an increase of up to 30% in comparison to the first extended batch experiment without in situ product removal. Itaconic acid was recovered with a purity of at least 95% and high concentrations above 300 g/L in the eluate.

CONCLUSION

Integration of product separation via adsorption into the bioprocess was successfully conducted and improved the efficiency of itaconic acid production. Raman spectroscopy was proven to be a reliable tool for online monitoring of various metabolites and facilitated design and validation of the complex separation and feed process. The general process concept can be transferred to the production of various similar bioproducts, expanding the tool kit for design of innovative biorefinery processes.

Interdisciplinary development of an overall process concept from glucose to 4,5-dimethyl-1,3-dioxolane via 2,3-butanediol

To reduce carbon dioxide emissions, carbon-neutral fuels have recently gained renewed attention. Here we show the development and evaluation of process routes for the production of such a fuel, the cyclic acetal 4,5-dimethyl-1,3-dioxolane, from glucose via 2,3-butanediol. The selected process routes are based on the sequential use of microbes, enzymes and chemo-catalysts in order to exploit the full potential of the different catalyst systems through a tailor-made combination. The catalysts (microbes, enzymes, chemo-catalysts) and the reaction medium selected for each conversion step are key factors in the development of the respective production methods. The production of the intermediate 2,3-butanediol by combined microbial and enzyme catalysis is compared to the conventional microbial route from glucose in terms of specific energy demand and overall yield, with the conventional route remaining more efficient. In order to be competitive with current 2,3-butanediol production, the key performance indicator, enzyme stability to high aldehyde concentrations, needs to be increased. The target value for the enzyme stability is an acetaldehyde concentration of 600 mM, which is higher than the current maximum concentration (200 mM) by a factor of three.

Holistic Approach to Process Design and Scale-Up for Itaconic Acid Production from Crude Substrates

Bio-based bulk chemicals such as carboxylic acids continue to struggle to compete with their fossil counterparts on an economic basis. One possibility to improve the economic feasibility is the use of crude substrates in biorefineries. However, impurities in these substrates pose challenges in fermentation and purification, requiring interdisciplinary research. This work demonstrates a holistic approach to biorefinery process development, using itaconic acid production on thick juice based on sugar beets with Ustilago sp. as an example. A conceptual process design with data from artificially prepared solutions and literature data from fermentation on glucose guides the simultaneous development of the upstream and downstream processes up to a 100 L scale. Techno-economic analysis reveals substrate consumption as the main constituent of production costs and therefore, the product yield is the driver of process economics. Aligning pH-adjusting agents in the fermentation and the downstream process is a central lever for product recovery. Experiments show that fermentation can be transferred from glucose to thick juice by changing the feeding profile. In downstream processing, an additional decolorization step is necessary to remove impurities accompanying the crude substrate. Moreover, we observe an increased use of pH-adjusting agents compared to process simulations.

Influence of Mixed Salts on Retention Behavior of Model Proteins in Cation Exchange Chromatography

Mobile phase composition is an important factor for a further improvement of ion exchange chromatography steps of proteins. In this work, the effects of mixed salts on the retention factors of the two model proteins lysozyme (LYZ) and bovine serum albumin (BSA) in cation exchange chromatography (CEC) were investigated and compared to effects previously observed in hydrophobic interaction chromatography (HIC). The model equation describing the effects in HIC was adjusted for linear gradient elution experiments in CEC. The investigated salts were sodium chloride, sodium sulfate, ammonium chloride and ammonium sulfate. By varying binary salt mixtures as well as using pure salts, model parameters were determined. The normalized root mean square error (NRMSE) of the predicted retention factors for the calibration runs was 4.1% for BSA and 3.1% for LYZ. Additional validation experiments proved the ability of the model to describe and predict retention behavior of the proteins for further salt compositions. Hereby, the NRMSE values for BSA and LYZ were 2.0% and 1.5%, respectively. While the retention factors of LYZ changed linearly with the salt composition, non-linearities in the impact of the anion composition were found for BSA. This was contributed to an overlay of a synergetic salt effect on a protein-specific effect by sulfate on BSA with non-specific effects of the ions for CEC. However, the impact of the synergetic effects on protein separation is lower for CEC than for HIC, as mixed salts do not increase the separation of these proteins. The best salt composition for separating BSA and LYZ is pure ammonium sulfate. Thus, synergetic salt effects can also occur in CEC, but they have a lower impact than in HIC.

Respiration-based investigation of adsorbent-bioprocess compatibility

BACKGROUND

The efficiency of downstream processes plays a crucial role in the transition from conventional petrochemical processes to sustainable biotechnological production routes. One promising candidate for product separation from fermentations with low energy demand and high selectivity is the adsorption of the target product on hydrophobic adsorbents. However, only limited knowledge exists about the interaction of these adsorbents and the bioprocess. The bioprocess could possibly be harmed by the release of inhibitory components from the adsorbent surface. Another possibility is co-adsorption of essential nutrients, especially in an in situ application, making these nutrients unavailable to the applied microorganism.

RESULTS

A test protocol investigating adsorbent-bioprocess compatibility was designed and applied on a variety of adsorbents. Inhibitor release and nutrient adsorption was studied in an isolated manner. Respiratory data recorded by a RAMOS device was used to assess the influence of the adsorbents on the cultivation in three different microbial systems for up to six different adsorbents per system. While no inhibitor release was detected in our investigations, adsorption of different essential nutrients was observed.

CONCLUSION

The application of adsorption for product recovery from the bioprocess was proven to be generally possible, but nutrient adsorption has to be assessed for each application individually. To account for nutrient adsorption, adsorptive product separation should only be applied after sufficient microbial growth. Moreover, concentrations of co-adsorbed nutrients need to be increased to compensate nutrient loss. The presented protocol enables an investigation of adsorbent-bioprocess compatibility with high-throughput and limited effort.

Evaluation of a Prototype for Electrochemical pH-Shift Crystallization of Succinic Acid

Downstream processing of biotechnologically produced carboxylic acids, such as succinic acid, poses environmental and economic challenges. Conventional downstream processes cause large amounts of waste salts, which have to be purified or disposed of. Therefore, lean and waste-free downstream processes are necessary for the biotechnological production of succinic acid. Electrochemical downstream processes gain especially significant attention due to low chemical consumption and waste reduction. This work presents the pH-dependent solid-liquid equilibrium of succinic acid, a prototype for electrochemical pH-shift crystallization processes, and its characterization. Based on the supersaturation, energy consumption, and electrochemical protonation efficiency the proposed electrochemical pH-shift crystallization is evaluated. This evaluation highlights the potential of the proposed electrochemical crystallization processes as waste-free and economically attractive processes for bio-based succinic acid production.

Extracorporeal Hyperoxygenation Therapy (EHT) for Carbon Monoxide Poisoning: In-Vitro Proof of Principle

Carbon monoxide (CO) poisoning is the leading cause of poisoning-related deaths globally. The currently available therapy options are normobaric oxygen (NBO) and hyperbaric oxygen (HBO). While NBO lacks in efficacy, HBO is not available in all areas and countries. We present a novel method, extracorporeal hyperoxygenation therapy (EHT), for the treatment of CO poisoning that eliminates the CO by treating blood extracorporeally at elevated oxygen partial pressure. In this study, we proof the principle of the method in vitro using procine blood: Firstly, we investigated the difference in the CO elimination of a hollow fibre membrane oxygenator and a specifically designed batch oxygenator based on the bubble oxygenator principle at elevated pressures (1, 3 bar). Secondly, the batch oxygenator was redesigned and tested for a broader range of pressures (1, 3, 5, 7 bar) and temperatures (23, 30, 37 °C). So far, the shortest measured carboxyhemoglobin half-life in the blood was 21.32 min. In conclusion, EHT has the potential to provide an easily available and effective method for the treatment of CO poisoning.

MIXed plastics biodegradation and UPcycling using microbial communities: EU Horizon 2020 project MIX-UP started January 2020

This article introduces the EU Horizon 2020 research project MIX-UP, "Mixed plastics biodegradation and upcycling using microbial communities". The project focuses on changing the traditional linear value chain of plastics to a sustainable, biodegradable based one. Plastic mixtures contain five of the top six fossil-based recalcitrant plastics [polyethylene (PE), polyurethane (PUR), polypropylene (PP), polyethylene terephthalate (PET), polystyrene (PS)], along with upcoming bioplastics polyhydroxyalkanoate (PHA) and polylactate (PLA) will be used as feedstock for microbial transformations. Consecutive controlled enzymatic and microbial degradation of mechanically pre-treated plastics wastes combined with subsequent microbial conversion to polymers and value-added chemicals by mixed cultures. Known plastic-degrading enzymes will be optimised by integrated protein engineering to achieve high specific binding capacities, stability, and catalytic efficacy towards a broad spectrum of plastic polymers under high salt and temperature conditions. Another focus lies in the search and isolation of novel enzymes active on recalcitrant polymers. MIX-UP will formulate enzyme cocktails tailored to specific waste streams and strives to enhance enzyme production significantly. In vivo and in vitro application of these cocktails enable stable, self-sustaining microbiomes to convert the released plastic monomers selectively into value-added products, key building blocks, and biomass. Any remaining material recalcitrant to the enzymatic activities will be recirculated into the process by physicochemical treatment. The Chinese-European MIX-UP consortium is multidisciplinary and industry-participating to address the market need for novel sustainable routes to valorise plastic waste streams. The project's new workflow realises a circular (bio)plastic economy and adds value to present poorly recycled plastic wastes where mechanical and chemical plastic recycling show limits.

Metabolic and process engineering for microbial production of protocatechuate with Corynebacterium glutamicum

3,4-Dihydroxybenzoate (protocatechuate, PCA) is a phenolic compound naturally found in edible vegetables and medicinal herbs. PCA is of high interest in the chemical industry and has wide potential for pharmaceutical applications. We designed and constructed a novel Corynebacterium glutamicum strain to enable the efficient utilization of d-xylose for microbial production of PCA. Shake flask cultivation of the engineered strain showed a maximum PCA titer of 62.1 ± 12.1 mM (9.6 ± 1.9 g L^-1 ) from d-xylose as the primary carbon and energy source. The corresponding yield was 0.33 C-mol PCA per C-mol d-xylose, which corresponds to 38% of the maximum theoretical yield. Under growth-decoupled bioreactor conditions, a comparable PCA titer and a total amount of 16.5 ± 1.1 g PCA could be achieved when d-glucose and d-xylose were combined as orthogonal carbon substrates for biocatalyst provision and product synthesis, respectively. Downstream processing of PCA was realized via electrochemically induced crystallization by taking advantage of the pH-dependent properties of PCA. This resulted in a maximum final purity of 95.4%. The established PCA production process represents a highly sustainable approach, which will serve as a blueprint for the bio-based production of other hydroxybenzoic acids from alternative sugar feedstocks.