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Spontaneous mutations in a regulatory gene induce phenotypic heterogeneity and adaptation of Ralstonia solanacearum to changing environments

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Perrier, Anthony | Barlet, Xavier | Rengel, David | Prior, Philippe | Poussier, Stéphane | Genin, Stéphane | Guidot, Alice

Edité par CCSD ; Society for Applied Microbiology and Wiley-Blackwell -

International audience. An evolution experiment with the bacterial plant pathogen Ralstonia solanacearum revealed that several adap-tive mutations conferring enhanced fitness in plants arose in the efpR gene encoding a regulator of virulence and metabolic functions. In this study, we found that an efpR mutant systematically displays colonies with two morphotypes: the type S ('smooth', similar to the wild type) and the type EV ('efpR variant'). We demonstrated that the efpH gene, a homologue of efpR, plays a key role in the control of phenotypic heterogeneity, the ΔefpR-ΔefpH double mutant being stably locked into the EV type. Using mixed infection assays, we demonstrated that the type EV is metabolically more proficient than the type S and displays fitness gain in specific environments, whereas the type S has a better fitness into the plant environment. We provide evidence that this efpR-dependent phenotypic heterogeneity is a general feature of strains of the R. solanacearum species complex and could occur in natural conditions. This study highlights the potential role of phenotypic hetero-geneity in this plant pathogen as an adaptive trait to changing environments.

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