A novel E. coli strain shows controllable leakiness for extracellular
production of recombinant proteins
Abstract
Recombinant proteins in Escherichia coli are usually expressed inside
the cell. With the growing interest in continuous cultivation, secretion
of product to the medium is not only a benefit, but a necessity in
future bioprocessing. In this study, we present the X-press strain, a
novel E. coli production host for growth decoupled, extracellular
recombinant protein production. We investigated the effect of the
process parameters temperature and specific glucose uptake rate (qS) on
the strain’s growth, productivity, lysis and leakiness, to find the
parameter space allowing extracellular protein production. Two model
proteins were used, Protein A and a VHH single-domain antibody, and
performance was compared to the industrial standard strain BL21(DE3). We
show that inducible growth repression in the X-press strain greatly
mitigates the effect of metabolic burden under different process
conditions. Furthermore, temperature and qS were used to control
productivity and leakiness. In the X-press strain, extracellular Protein
A and VHH titer reached up to 349 mg/g and 19.6 mg/g, respectively,
comprising up to 90% of total soluble product, while keeping cell lysis
at a minimum. Our findings demonstrate that the X-press strain
constitutes a valuable host for extracellular production of recombinant
protein with E. coli.