FIG 6.

Model of the P. luminescens 2° cell alternative life cycle in the rhizosphere. During the insect infection cycle, single P. luminescens cells undergo phenotypic switching from the 1° to the 2° phenotype. The 2° cells cannot reassociate with the nematode symbiosis partner and are left behind in the soil when the nematodes leave the depleted insect cadaver. Then, the 2° cells chemotactically respond to plant root exudates and specifically colonize and attach to the roots. The metabolism of the bacteria adapts to plant-derived nutrients, and the cells protect the plants from phytopathogens. Since 2° cells are still pathogenic against insects, it can be assumed that they also protect the plant roots from insect predators.