Transposon sequencing reveals the essential gene set and genes enabling gut symbiosis in the insect symbiontCaballeronia insecticola

Abstract

AbstractCaballeronia insecticolais a bacterium belonging to theBurkholderiagenussensu lato, able to colonize multiple environments like soils and the gut of the bean bugRiptortus pedestris. To identify the essential genome of a bacterium is a first step in the understanding of its lifestyles. We constructed a saturatedHimar1mariner transposon library and revealed by transposon-sequencing (Tn-seq) that 498 protein-coding genes constitute the essential genome ofC. insecticolafor growth in free-living conditions. By comparing essential gene sets ofC. insecticolaand seven relatedBurkholderia s.l.strains, only 120 common genes were identified indicating that a large part of the essential genome is strain-specific. In order to reproduce specific nutritional conditions that are present in the gut ofR. pedestris, we grew the mutant library in minimal media supplemented with candidate gut nutrients and identified several condition-dependent fitness-defect genes by Tn-seq. To validate the robustness of the approach, insertion mutants in six fitness genes were constructed and their growth-deficiency in media supplemented with the corresponding nutrient was confirmed. The mutants were further tested for their efficiency inR. pedestrisgut colonization, confirming that gluconeogenic carbon sources, taurine and inositol, are nutrients consumed by the symbiont in the gut.