초록
<P><B>Background</B></P><P>The production of recombinant proteins containing disulfide bonds in <I>Escherichia coli</I> is challenging. In most cases the protein of interest needs to be either targeted to the oxidizing periplasm or expressed in the cytoplasm in the form of inclusion bodies, then solubilized and re-folded in vitro. Both of these approaches have limitations. Previously we showed that soluble expression of disulfide bonded proteins in the cytoplasm of <I>E. coli</I> is possible at shake flask scale with a system, known as CyDisCo, which is based on co-expression of a protein of interest along with a sulfhydryl oxidase and a disulfide bond isomerase. With CyDisCo it is possible to produce disulfide bonded proteins in the presence of intact reducing pathways in the cytoplasm.</P><P><B>Results</B></P><P>Here we scaled up production of four disulfide bonded proteins to stirred tank bioreactors and achieved high cell densities and protein yields in glucose fed-batch fermentations, using an <I>E. coli</I> strain (BW25113) with the cytoplasmic reducing pathways intact. Even without process optimization production of purified human single chain IgA<SUB>1</SUB> antibody fragment reached 139 mg/L and hen avidin 71 mg/L, while purified yields of human growth hormone 1 and interleukin 6 were around 1 g/L. Preliminary results show that human growth hormone 1 was also efficiently produced in fermentations of W3110 strain and when glucose was replaced with glycerol as the carbon source.</P><P><B>Conclusions</B></P><P>Our results show for the first time that efficient production of high yields of soluble disulfide bonded proteins in the cytoplasm of <I>E. coli</I> with the reducing pathways intact is feasible to scale-up to bioreactor cultivations on chemically defined minimal media.</P><P><B>Electronic supplementary material</B></P><P>The online version of this article (doi:10.1186/s12934-017-0721-x) contains supplementary material, which is available to authorized users.</P>