Exploration of cell lysis in a bioreactor using Escherichia coli expressing single-chain variable-domain antibody fragments

Cell lysis has long been a process problem in protein expression using bacterial hosts. To explore the pathways involved in cell lysis in a bioreactor, Escherichia coli strain W3110 was used as the host to express single-chain variable-domain antibody fragments (scFv). Under the same fermentation conditions, E. coli strain W3110 expressing a humanized scFv entered the viable but nonculturable (VBNC) state 6 h before the wild-type strain, and the accumulation of the scFv within the cells accelerated cell lysis. At the transcriptional level, the scFv not only altered the expression of rpoH, dnaK, dnaJ, groES, and groEL in the heat stress response, but also rpoS, gadE, and gadX in the acid stress response pathway and sodA and katE in the oxygen stress response pathway. During cell lysis in a fermenter, the expression of the membrane protein-encoding genes ompA, ompC, ompW, and ompX significantly decreased, and the high-level expression of rpoE was not sustained. These findings provide new insights into cell lysis as well as a theoretical foundation for improving fermentation conditions and engineering bacteria to minimize cell lysis during fermentation.