Unraveling the potential and constraints associated with corn steep liquor as a nutrient source for industrial fermentations.

Abstract

Costly complex media components such as yeast extract and peptone are still widely used in industrial bioprocesses, despite their ill-defined composition. Side stream products such as corn steep liquor (CSL) present a compelling economical alternative that contains valuable nutrients required for microbial growth, that is, nitrogen and amino acids, but also vitamins, trace elements, and other minerals. However, as a side stream product, CSL may be subject to batch-to-batch variations and compositional heterogeneity. In this study, the Respiration Activity MOnitoring System designed for shake flasks (RAMOS) and 96-well microtiter plates (μTOM) were applied to investigate the potential and constraints of CSL utilization for two model microorganisms: E. coli and B. subtilis. Considering the dry substance content of complex nutrients involved, CSL-based media are more efficient in biomass production than the common lysogeny broth (LB) medium, containing 5 g/L yeast extract, 10 g/L peptone, and 5 g/L NaCl. At a glucose to CSL (glucose/CSL, g/g) ratio of 1/1 (g/g) and 2/1 (g/g), a secondary substrate limitation occurred in E. coli and B. subtilis cultivations, respectively. The study sheds light on differences in the metabolic activity of the two applied model organisms between varying CSL batches, which relate to CSL origin and production process, as well as the effect of targeted nutrient supplementation. Through a targeted nutrient supplementation, the most limiting component of the CSL-glucose medium used for these applied model microorganisms was identified to be ammonium nitrogen. This study proves the suitability of CSL as an alternative nutrient source for E. coli and B. subtilis. The RAMOS and μTOM technique detected differences between CSL batches, allowing easy and early identification of varying batches. A consistent performance of the CSL batches in E. coli and B. subtilis cultivations was demonstrated.