PhD ThesisSalmonella enterica is considered zoonotic pathogen with capability to colonies on
range of plants and animals allowing transmission between them. Whole genome
sequence analysis of S. enterica generates a phylogenetic tree comprising of three
clades: A1, A2 and B. These 3 clades encompass the known 2,600 serovars used to
type S. enterica during clinical outbreaks of salmonellosis. S. enterica exploits the
bacterial flagellum to be motile in liquid environments and over surfaces. The genetic
regulation of flagellar assembly is an elegant and harmonious system driving
assembly of the flagellum from the base upwards.
We surveyed the response and changes to flagellar regulation in a cohort of S.
enterica serovars. Our analysis encompassed examining phenotypic motility, flagellar
gene expression and flagellar abundance depending on nutrient composition. We
demonstrated that the timing of flagellar gene expression is consistent across the
species but the magnitude of flagellar gene expression varies significantly. The S.
enterica flagellar system is bistable, producing a heterogeneous population of motile
cells. Our data suggested that population heterogeneity plays a role in the adaptation
of S. enterica serovars with respect to motility.
The great similarity of the flagellum systems between S.enterica and E.coli gave
us a reason to study why flagellar regulation in S.enterica differed from E. coli.
Indeed, we replaced the master flagellar regulators, flhDC from E.coli into the S.
enterica. We found a significant variation in FlhD4C2 activity through mixing flhD and
flhC between both organisms. In conclusion, the diversity and changes we observe in
just a small subset of S. enterica serovars and by introducing flhDC homologues has
made us reconsider a number of assumptions we make about the regulation of the
flagellar system based on model-domesticated strains of S. enterica.Ministry of Higher Education and Scientific Research in Ira
