Abstract
BackgroundMedia containing yeast extracts and other complex raw materials are widely used for the cultivation of microorganisms. However, variations in the specific nutrient composition can occur, due to differences in the complex raw material ingredients and in the production of these components. These lot-to-lot variations can affect growth rate, product yield and product quality in laboratory investigations and biopharmaceutical production processes. In the FDA’s Process Analytical Technology (PAT) initiative, the control and assessment of the quality of critical raw materials is one key aspect to maintain product quality and consistency. In this study, the Respiration Activity Monitoring System (RAMOS) was used to evaluate the impact of different yeast extracts and commercial complex auto-induction medium lots on metabolic activity and product yield of four recombinant Escherichia coli variants encoding different enzymes.ResultsUnder non-induced conditions, the oxygen transfer rate (OTR) of E. coli was not affected by a variation of the supplemented yeast extract lot. The comparison of E. coli cultivations under induced conditions exhibited tremendous differences in OTR profiles and volumetric activity for all investigated yeast extract lots of different suppliers as well as lots of the same supplier independent of the E. coli variant. Cultivation in the commercial auto-induction medium lots revealed the same reproducible variations. In cultivations with parallel offline analysis, the highest volumetric activity was found at different cultivation times. Only by online monitoring of the cultures, a distinct cultivation phase (e.g. glycerol depletion) could be detected and chosen for comparable and reproducible offline analysis of the yield of functional product.ConclusionsThis work proves that cultivations conducted in complex media may be prone to significant variation in final product quality and quantity if the quality of the raw material for medium preparation is not thoroughly checked. In this study, the RAMOS technique enabled a reliable and reproducible screening and phenotyping of complex raw material lots by online measurement of the respiration activity. Consequently, complex raw material lots can efficiently be assessed if the distinct effects on culture behavior and final product quality and quantity are visualized.Electronic supplementary materialThe online version of this article (doi:10.1186/s12934-014-0149-5) contains supplementary material, which is available to authorized users.
Highlights
Media containing yeast extracts and other complex raw materials are widely used for the cultivation of microorganisms
Cultivation under non-induced conditions Cultivations were conducted in the Respiration Activity Monitoring System (RAMOS) device under non-inducing conditions in terrific broth (TB) medium to evaluate the influence of the eight yeast extract lots (Table 1) on growth behavior of E. coli
Under non-induced conditions, respiration activity of E. coli was not affected by a variation of the supplemented yeast extract lot
Summary
Media containing yeast extracts and other complex raw materials are widely used for the cultivation of microorganisms. Variations in the specific nutrient composition can occur, due to differences in the complex raw material ingredients and in the production of these components These lot-to-lot variations can affect growth rate, product yield and product quality in laboratory investigations and biopharmaceutical production processes. In the FDA’s Process Analytical Technology (PAT) initiative, the control and assessment of the quality of critical raw materials is one key aspect to maintain product quality and consistency. When cultivating a Penicillium strain, BaracatPereira et al reported that possible precursors or inducers of cAMP in yeast extract could enhance the induction of protein expression [13] Based on these findings, the identification of yeast extract ingredients promoting growth and production rate is of special interest to achieve a consistent fermentation performance. Even a detailed evaluation of many ingredients in yeast extract might not automatically allow reliable conclusions on yield and quality of a specific product
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