Lights off - Role of bioluminescence for the biology of the biocontrol agent .

Bioluminescence is found across various organisms having crucial functions for biotic interactions and stress adaptation. The only known terrestrial bioluminescent bacteria are entomopathogenic bacteria of the genus . However, the reason why these bacteria produce light is not understood. exists in two cell forms called primary (1°) and secondary (2°) cells. The 1° cells colonize the nematode symbiosis partner and produce bright light, whereas 2° cells colonize plant roots only emitting weak light. Here we show that bioluminescence is important but not essential for the biology of the bacteria. Deletion of the operon in 1° cells impaired insect pathogenicity and nematode interaction. The complete loss of light of 2° cells resulted in enhanced plant root colonization, enhanced haemolysis, and reduced oxidative stress adaptation. Since bioluminescence is not essential for the survival of the bacteria, Δ 1° and 2° emerged as useful tools for bioluminescence-based reporter assays.