ydfD encodes a novel lytic protein in Escherichia coli

Bacteria carry a number of genes that cause cell growth arrest or cell lysis upon expression. Notably, defective prophages retain many lysis proteins. Here, we identified a novel lytic gene, ydfD, on the Qin prophage segment of the Escherichia coli genome. YdfD lyses 99.9% of cells within 2 h of its induction. The co-expression of the upstream gene, dicB, encoding a cell division inhibitor, as well as sulA, encoding another cell division inhibitor, abolished YdfD-induced cell lysis. These results imply that YdfD-induced lysis is a cell division-dependent event. We further found that by deleting the hydrophobic 22-residue N-terminal domain, the resulting 42-residue C-terminal domain was still toxic to cause cell lysis. We propose that YdfD, associated with the cytoplasmic membrane, inhibits an essential cellular process(s).