title: FliZ is a global regulatory protein affecting the expression of flagellar and virulence genes in individual Xenorhabdus nematophila bacterial cells.
abstract: Heterogeneity in the expression of various bacterial genes has been shown to result in the presence of individuals with different phenotypes within clonal bacterial populations. The genes specifying motility and flagellar functions are coordinately regulated and form a complex regulon, the flagellar regulon. Complex interplay has recently been demonstrated in the regulation of flagellar and virulence gene expression in many bacterial pathogens. We show here that FliZ, a DNA-binding protein, plays a key role in the insect pathogen, Xenorhabdus nematophila, affecting not only hemolysin production and virulence in insects, but efficient swimming motility. RNA-Seq analysis identified FliZ as a global regulatory protein controlling the expression of 278 Xenorhabdus genes either directly or indirectly. FliZ is required for the efficient expression of all flagellar genes, probably through its positive feedback loop, which controls expression of the flhDC operon, the master regulator of the flagellar circuit. FliZ also up- or downregulates the expression of numerous genes encoding non-flagellar proteins potentially involved in key steps of the Xenorhabdus lifecycle. Single-cell analysis revealed the bimodal expression of six identified markers of the FliZ regulon during exponential growth of the bacterial population. In addition, a combination of fluorescence-activated cell sorting and RT-qPCR quantification showed that this bimodality generated a mixed population of cells either expressing ("ON state") or not expressing ("OFF state") FliZ-dependent genes. Moreover, studies of a bacterial population exposed to a graded series of FliZ concentrations showed that FliZ functioned as a rheostat, controlling the rate of transition between the "OFF" and "ON" states in individuals. FliZ thus plays a key role in cell fate decisions, by transiently creating individuals with different potentials for motility and host interactions.
authors.affiliation: INRA, UMR 1333 Laboratoire DGIMI, Montpellier, France ; Université Montpellier 2, UMR 1333 Laboratoire DGIMI, Montpellier, France.
authors.forename: Grégory
authors.initials: G
authors.lastname: Jubelin
authors.forename: Anne
authors.initials: A
authors.lastname: Lanois
authors.forename: Dany
authors.initials: D
authors.lastname: Severac
authors.forename: Stéphanie
authors.initials: S
authors.lastname: Rialle
authors.forename: Cyrille
authors.initials: C
authors.lastname: Longin
authors.forename: Sophie
authors.initials: S
authors.lastname: Gaudriault
authors.forename: Alain
authors.initials: A
authors.lastname: Givaudan
mesh_terms: D000818:Animals; D001426:Bacterial Proteins / Q000096:biosynthesis* / Q000235:genetics; D004268:DNA-Binding Proteins / Q000096:biosynthesis* / Q000235:genetics; D005407:Flagella / Q000235:genetics / Q000378:metabolism*; D005434:Flow Cytometry; D015964:Gene Expression Regulation, Bacterial; D054884:Host-Pathogen Interactions; D006801:Humans; D007313:Insecta / Q000382:microbiology; D018085:Regulon / Q000235:genetics; D059010:Single-Cell Analysis; D014774:Virulence / Q000235:genetics; D020593:Xenorhabdus / Q000235:genetics* / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D004268:DNA-Binding Proteins