*2.3.2 Genes and regulation*

The *rtx* gene cluster is encoded near the CTXφ phage, but their regulation is not linked [98]. RtxA is secreted by its own unorthodox T1SS that requires two ABC transporters for the secretion [97]. The *rtx* locus is composed of 2 operons, the first one is left oriented and contains a conserved hypothetical gene VC1449, the activator (*rtxC*) and the toxin (*rtxA*). The second, right oriented, contains the ABC transporter (*rtxB*) and the fusion protein (*rtxD*) genes, plus the extra ABC transporter *rtxE*. The *tolC* is encoded further. The RtxA toxin secretion is optimal during the exponential phase of growth but is inhibited in stationary phase [98].
