Regulatory role of Photorhabdus bioluminescence in belowground multi-trophic interactions

Heterorhabditis are insect parasitic nematodes that establish a close symbiotic relationship with bacteria from the genus Photorhabdus. Together Heterorhabditis and Photorhabdus are highly pathogenic to insects and are, therefore, broadly used as biological control agents in agriculture. Heterorhabditis nematodes break into soil-dwelling insects and release their symbiotic Photorhabdus bacteria. The bacteria multiply and produce toxins leading ultimately to the death of the insect. The nematodes then proliferate into the dead insect for several generations. Upon resource depletion, the nematodes re-associate with its symbiotic bacteria and emerge from the cadaver looking for a new host. Interestingly, during the infection process Photorhabdus bacteria produce and emit blue light, making the infected insect to glow. The prevalence of bioluminescence in the Photorhabdus genus, which is thought to be an energetically costly process, strongly suggests that this particular trait confer an adaptive benefit to the bacteria, to the nematode, or to both, although the evidence in this context is still lacking. We hypothesize that adaptive benefits of the blue light produced by Photorhabdus bacteria are derived from the modulation of belowground multi-trophic interactions between plants, herbivorous and carnivorous insects, and their nematode hosts. The aim of this project is to take a multidisciplinary approach, by using these organisms and developing molecular tools, to contribute to a better understanding of the potential adaptive advantages of bioluminescence.