Abstract
Pantoea is a versatile genus of bacteria with both plant- and animal-pathogenic strains, some of which have been suggested to cause human infections. There is, however, limited knowledge on the potential determinants used for host association and pathogenesis in animal systems. In this study, we used the model host Dictyostelium discoideum to show that isolates of Pantoeaananatis exhibit differential grazing susceptibility, with some being resistant to grazing by the amoebae. We carried out a high-throughput genetic screen of one grazing-resistant isolate, P.ananatis BRT175, using the D.discoideum pathosystem to identify genes responsible for the resistance phenotype. Among the 26 candidate genes involved in grazing resistance, we identified rhlA and rhlB, which we show are involved in the biosynthesis of a biosurfactant that enables swarming motility in P.ananatis BRT175. Using liquid chromatography-mass spectrometry (LC-MS), the biosurfactant was shown to be a glycolipid with monohexose-C10-C10 as the primary congener. We show that this novel glycolipid biosurfactant is cytotoxic to the amoebae and is capable of compromising cellular integrity, leading to cell lysis. The production of this biosurfactant may be important for bacterial survival in the environment and could contribute to the establishment of opportunistic infections. IMPORTANCE The genetic factors used for host interaction by the opportunistic human pathogen Pantoea ananatis are largely unknown. We identified two genes that are important for the production of a biosurfactant that confers grazing resistance against the social amoeba Dictyostelium discoideum. We show that the biosurfactant, which exhibits cytotoxicity toward the amoebae, is a glycolipid that incorporates a hexose rather than rhamnose. The production of this biosurfactant may confer a competitive advantage in the environment and could potentially contribute to the establishment of opportunistic infections.
Highlights
Pantoea is a versatile genus of bacteria with both plant- and animalpathogenic strains, some of which have been suggested to cause human infections
The sister taxon isolate to P. ananatis BRT175, P. ananatis 17671, was one of the least grazing-resistant isolates, with plaque and spore formation being evident throughout the lawn
Sister isolates P. ananatis BRT175 and P. ananatis 17671 showed phenotypes on msphere.asm.org 9 the two extremes of the grazing resistance spectrum, supporting the presence of specific genetic factors that contribute to this phenotype
Summary
Pantoea is a versatile genus of bacteria with both plant- and animalpathogenic strains, some of which have been suggested to cause human infections. Quantitative growth assays have shown that closely related isolates of P. ananatis can vary greatly in their growth potential in plant and insect model hosts [13], suggesting the presence of specific genetic factors that mediate host association [14,15,16]. This has been explored further in a comparative genomics analysis of eight P. ananatis genomes, which determined that isolates readily exchange genetic factors involved in host- and niche-specific colonization [17]. We show that two genes, rhlA and rhlB, are involved in producing a novel biosurfactant that is cytotoxic to D. discoideum
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