Fig. 6: Proposed model for the dual role of CccR in bacterial competition and cell-to-cell communication.
From: A secreted effector with a dual role as a toxin and as a transcriptional factor
In CccR-producing cells, CccR represses its own expression. Under competition conditions, CccR is released into the extracellular milieu to relieve the autorepression. Released CccR enters target cells by engaging the TonB-dependent outer membrane transporter FhuA in a bacteriocin-like manner. In the presence of many prey cells (Left), secreted CccR is preferentially internalized by prey cells, where it AMPylates cell division protein FtsZ, leading to cell filamentation and growth arrest. Following the decrease in prey cells (Right), secreted CccR is internalized by sister cells to repress cccR expression by acting as a transcriptional regulator, informing the population that its production is unnecessary. Under this condition, CccR may also act as a global regulator that regulates expression of genes involved in iron acquisition, motility, and energy production to coordinate bacterial behaviors and increase bacterial fitness. The potential transcriptional regulatory effects of CccR in prey cells are unclear at present.
