(451c) On the Use of Periodically Inverted Assay Tubes As a Screening Platform for Recombinant Escherichia coli Cultures

The screening of strains and culture conditions is a routine operation in biotechnology settings.  Here we illustrate the use of commercial Vacutainer™ assay tubes agitated by successive periodic inversions as an alternative platform to conduct early development culture experiments of two recombinant strains of Escherichia coli. As a model system, we use two E. coli strains of biopharmaceutical relevance: (a) a C41 derived strain producer of a monoclonal antibody fragment (Fab) and a C41 strain producer of a dimer of the globular region of an influenza antigen. Tubes (effective volume of 3 mL) were gently agitated by periodic inversions in a commercial rotational mixing system (ATR Rotamix, USA).  Experiments were conducted using three growth media formulations for E. coli with and without replacement of the air in the tube head space. We compared the culture performance of the periodically inverting assay tube mixing system (pITMS for short) with that of shake flasks (150 mL of effective volume) and fully instrumented bioreactors (1.3 L of effective volume) for the same strains and culture conditions. Results produced in the pITMS exhibit high reproducibility and low variance among different culture experiments. Even though the growth rate (µ in h^-1) was different in each type of reactor, the general growth behavior of the bacterial culture and the levels of protein expression in assay tubes was practically the same as in the shake flasks and in bioreactor, demonstrating the predictive potential of the pITMS.

Our results suggest that the pITMS is a practical alternative to conduct parallel screening experiments that can resemble the behavior of aerobic bacterial cultures performed in flasks and instrumented bioreactors.