Towards process intensification: Enhancing growth, production and robustness of Corynebacterium glutamicum on spent sulfite liquor

Abstract

Bioprocesses that efficiently utilize sustainable resources for manufacturing of highvalue products are an important enabler for the urgently needed transition towardsa bio-based circular economy. To achieve economic feasibility of such a process, intensification strategies have to be considered in the development stage. A previously established SSL-based fed-batch process utilizing C. glutamicum for the production of the antimicrobial peptide pediocin PA-1 was analyzed for a potential bioprocess intensification. Several problems in this bioprocess were identified that reduced the efficiency and hindered the envisioned intensification towards a repetitive fed-batch.Problems in the batch phase such a long unpredictable lag-phase, low biomass yield and incomplete substrate utilization were attributed to inhibitors present in SSL and the necessary detoxification by cells. Further, problems in the fed-batch of the original process such as overfeeding were hypothesed to be directly related to the aforementionedissues of the batch-phase and the consequent poor starting conditions. To resolve these problems, increase the reliability of the process and provide comparable starting conditions for subsequent investigations in the fed-batch phase, the in oculum amount was adapted. By increasing the in oculum size, the detoxification load per cellis reduced, resulting in less variability, shorter lag-phases and higher achieved biomassconcentrations. The fed-batch pH value and carbon-phosphorous ratio were identified as promising factors influencing the pediocin production and investigated using a threelevel full-factorial experimental design. Both the pH value and the C:P-ratio as well as their interaction were shown to have a significant influence on the maximum achieved pediocin titre. The obtained data was further checked for consistency by elemental balancing and utilized to establish a mechanistic model. The substrate utilization was modelled sucessfully with monod-like equations and a NRMSE of below 10% forall considered substrates (glucose, xylose, mannose, acetate). Modeling the biomass concentration failed to meet the set acceptance critereon (10%) with a 15% NMRSE.Analytical challenges associated with SSL matrix and the consequent inability to determine important factors such as the phosphate and product concentration preventeda successful modeling of the pediocin formation. After process intensification the developed biorefinery concept has potential for integration into existing pulp and papermills for production of high value products.