The mcf gene encodes a toxin that has been shown to destroy insect phagocytes and to cause disintegration of the insect midgut via apoptosis, producing
the characteristic ‘floppy’ phenotype of Photorhabdus-infected insects (Waterfield et al., 2003). The Kingscliff genome is syntenic with the US isolate across regions containing the tca, tcb and tcd pathogenicity islands that encode high-molecular-weight, multisubunit orally insecticidal toxins (see Figs S3, S4 and S5). The Tc toxins aid in the killing and bioconversion of the insect host by destroying the insect midgut and rendering the host incapable of further feeding (Forst & Nealson, 1996). Other toxins that are found in both the US and Australian isolates are the pirAB insecticidal binary VE 821 Caspase inhibitor toxin (Fig.
S6); which has been shown to have larvicidal activity (Waterfield et al., 2005; Ahantarig et al., 2009). In addition, the Kingscliff strain also contains the PVC cassettes (see Fig. S7) that consist of phage-like elements encoding a structure similar to an R-type pyocin (Yang et al., 2006). These PVC cassettes contain a number of phage-like ORFs that produce the structural part of the PVC and then one or more ORFs encoding putative toxins. Interestingly, the Kingscliff strain appears to lack the PVC pnf, which is present in the US isolate and has been associated with the destruction of insect blood cells (Yang et al., 2006). It has been speculated that the PVCs act like a syringe to deliver the encoded effector molecules to their target cells. The Kingscliff strain also contains the Type Three Secretion Systems (TTSSs) TTSS-1 and TTSS-2 (see Figs S8 and S9) described previously in the ATCC43949 strain (Wilkinson et al., 2009). The TTSS-2 secretion system is similar to one found in Vibrio parahaemolyticus and may be involved in human pathogenicity and intracellular (-)-p-Bromotetramisole Oxalate invasion. Figure 2 displays two example regions of difference between the P. asymbiotica ATCC43949 and
the P. asymbiotica Kingscliff strains. Figure 2a shows a polyketide synthase operon (encoding proteins that are similar to those required for gramicidin2 synthesis) that is present in P. asymbiotica ATCC43949 and absent from the corresponding region in P. asymbiotica Kingscliff. An interesting feature is the presence of phage proteins and transposases flanking the PKS genes. These transposable elements provide a potential mechanism for the horizontal transfer of genes between the two genomes. Conversely, the genomic region displayed in Fig. 2b shows a number of genes present in P. asymbiotica Kingscliff that are missing from same region in the ATCC43949 genome. One of these genes is tccZ, a gene of unknown function that is tightly linked to the insecticidal tcc-toxin loci.