Project description:Secretion systems are used as weapons by a variety of Gram-negative bacteria. Among them the Type VI Secretion System (T6SS) gained more interest throughout the last years. The system functions as a molecular nano-weapon: it is used in inter-kingdom competition by various bacteria to deliver toxic effectors in target cells. Here we describe the role of the T6SS in Photorhabdus laumondii subsp. laumondii strain DJC, an entomopathogenic biocontrol agent able to live in different environmental niches, such as in symbiosis with nematodes and in the rhizosphere on plant roots. Using bioinformatic and protein motif analyses we identified four T6SS gene clusters (T6SS-1, T6SS-2, T6SS-3 and T6SS-4) and multiple orphan T6SS related genes in the genome of P. laumondii. Furthermore, we highlighted 11 T6SS effector-immunity pairs, including three undescribed membrane disrupting effectors, each with putatively different antibacterial activities. By label-free mass spectrometry of P. laumondii wild type cells and respective T6SS-deficient strains, we could point out a cross-link between T6SS and other Photorhabdus’ virulence related mechanisms such as PVCs, T3SS and pyocins. Furthermore, a change in motility as well as in the secondary metabolism was observed upon T6SS-deficiency. Here, we shed light on the T6SS in P. laumondii DJC and suggesting a cross-link of various virulence mechanisms, which could help to gain knowledge on T6SS and better figure out the Photorhabdus ability to live in polymicrobial environments.
