Abstract
BackgroundThe production of value-added chemicals alongside biofuels from lignocellulosic hydrolysates is critical for developing economically viable biorefineries. Here, the production of propionic acid (PA), a potential building block for C3-based chemicals, from corn stover hydrolysate is investigated using the native PA-producing bacterium Propionibacterium acidipropionici.ResultsA wide range of culture conditions and process parameters were examined and experimentally optimized to maximize titer, rate, and yield of PA. The effect of gas sparging during fermentation was first examined, and N2 was found to exhibit improved performance over CO2. Subsequently, the effects of different hydrolysate concentrations, nitrogen sources, and neutralization agents were investigated. One of the best combinations found during batch experiments used yeast extract (YE) as the primary nitrogen source and NH4OH for pH control. This combination enabled PA titers of 30.8 g/L with a productivity of 0.40 g/L h from 76.8 g/L biomass sugars, while successfully minimizing lactic acid production. Due to the economic significance of downstream separations, increasing titers using fed-batch fermentation was examined by changing both feeding media and strategy. Continuous feeding of hydrolysate was found to be superior to pulsed feeding and combined with high YE concentrations increased PA titers to 62.7 g/L and improved the simultaneous utilization of different biomass sugars. Additionally, applying high YE supplementation maintains the lactic acid concentration below 4 g/L for the duration of the fermentation. Finally, with the aim of increasing productivity, high cell density fed-batch fermentations were conducted. PA titers increased to 64.7 g/L with a productivity of 2.35 g/L h for the batch stage and 0.77 g/L h for the overall process.ConclusionThese results highlight the importance of media and fermentation strategy to improve PA production. Overall, this work demonstrates the feasibility of producing PA from corn stover hydrolysate.
Highlights
The production of value-added chemicals alongside biofuels from lignocellulosic hydrolysates is critical for developing economically viable biorefineries
Evaluation of P. acidipropionici in mock DDAPH substrate and effects of CO2 and N2 on propionic acid (PA) production Dilute acid and hydrothermal pretreatment processes, such as the one utilized in the current study, often result in the formation of toxic compounds such as HMF, furfural, and acetic acid, and these compounds can inhibit microbial growth [31]
P. acidipropionici has been reported to be able to fix C O2 in the conversion step of pyruvate to oxaloacetate through pyruvate carboxylate [32, 33], which may allow for C O2 uptake and a corresponding PA yield enhancement during fermentation
Summary
The production of value-added chemicals alongside biofuels from lignocellulosic hydrolysates is critical for developing economically viable biorefineries. The production of propionic acid (PA), a potential building block for C3-based chemicals, from corn stover hydrolysate is investigated using the native PA-producing bacterium Propionibacterium acidipropionici. Lignocellulosic biomass is a promising feedstock for the production of sustainable biofuels [1] and building block chemicals [2]. It is well known that PA is produced through the dicarboxylic acid pathway in Propionibacteria under anaerobic conditions [22, 23]. This group of microorganisms simultaneously converts sugars to other carboxylic acids leading to a decreased PA yield. Stowers et al demonstrated that 150 kPa of headspace pressure in the fermentor can maintain the LA titer under 3 g/L in batch fermentation [28]
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