Scale-up of a competitive and low-cost medium for prodigiosin production in a S. marcescens culture using biphasic systems as an integrated in-situ recovery process

Abstract

Product inhibition is an undesirable effect during fermentation that causes not only low yields but also a reduction in bioproduction feasibility of certain molecules. Prodigiosin is a secondary metabolite with an intense red produced by different strains of Serratia marcescens. Several in-vitro activities such as anticancer, antibacterial, immunosuppressive, anti-malaria and bio-colorant properties, make it particularly attractive to the pharmaceutical, food and textile industries. However, production of this natural alkaloid can be dramatically affected by media components and its antimicrobial activity causes end-product inhibition, additional to the complexity of typical production media making downstream processing complex and thus increasing the final cost of the purified product. In this study an optimization of a low-cost media using different sources and concentrations of carbon and nitrogen were performed. Extractive fermentation was evaluated as an integrated recovery strategy by coupling the upstream stage with different volumes of mineral oil as an extractive phase and we addressed the feasibility of scaling-up such extractive fermentation using batch and continuous processes modes. Peanut and defatted soybean meal in a 40 g/L - 5.25 g/L ratio, at 25 °C, achieved the best results, obtaining 584 mg/L of prodigiosin. The coupling of the medium with mineral oil at a 5% v/v presented a 1.12-fold in the prodigiosin content, which represents a change from 674 mg/L to 756 mg/L; and a 2-fold in cell growth. At scale-up tests, prodigiosin direct extraction produced in batch mode resulted in a prodigiosin concentration of 1282 mg/L. While continuous fermentation reached a concentration of 493 mg/L in steady state, which represents a 1.5-fold in the production rate compared to batch. A mathematical model, using Logistic and Luedeking-Piret equation was used to describe the microbial growth and product to correlate biomass and pigment production, obtaining correlation coefficients above 0.9747. The obtained results provide an opportunity to enhance prodigiosin production at the industrial level by alleviating end-product inhibition phenomenon using a two-phase system for in-situ primary recovery and putting in perspective with an economical approach. Also, this proposed strategy opens the possibility to transfer this experimental approach, for the recovery of several other hydrophobic molecules.