Defensive Function of Transposable Elements in Bacteria

Abstract

It has been widely debated whether transposable elements have a positive or a negative effect on their host cells. This study demonstrated that transposable elements, specifically insertion sequences (ISs), can adopt a defensive role in <i>Escherichia coli</i>. In three different <i>E. coli</i> strains (S17, DH5α, and Nissle 1917), IS1 and IS10 rapidly disrupted the <i>I-CeuI</i> gene (encoding I-CeuI endonuclease) on the plasmid pLO11-ICeuI as early as the first generation, despite the gene-circuit being under control of an arabinose promoter. Proteomics analysis showed that the protein abundance profile of <i>E. coli</i> DH5α with pLO11-ICeuI in the fifth generation was nearly opposite to that of control strain (<i>E. coli</i> with pLO11, no I-CeuI). The DNA damage caused by the leaky expression of <i>I-CeuI</i> was enough to trigger a SOS response and alter lipid synthesis, ribosomal activity, RNA/DNA metabolism, central dogma and cell cycle processes in <i>E. coli</i> DH5α. After the ISs disrupted the expression of <i>I-CeuI</i>, cells fully recovered by the 31st generation had a protein abundance profile similar to that of the control strain. This study showed that ISs readily mutated a harmful gene which subsequently restored host fitness. These observations have implications for the stability of designed gene circuits in synthetic biology.