Campylobacter jejuni : deciphering the role of F1hF in flagellar biogenesis

• Main Author: Stoakes, Emily Anne
• Published: University of Warwick 2017
• Subjects: 610; QR Microbiology
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.752463

Campylobacter jejuni is one the leading causes of food poisoning in the UK. Motility in C. jejuni is key to its survival within the gut and other environments. Without the two flagella, one at either end of the cell, it is highly attenuated to cause disease. As the flagellar structure is imperative to Campylobacters lifestyle, studying the regulation of flagella synthesis is important. Unlike other bacteria, Campylobacter lacks a master regulator atop the flagella synthesis pathway. It does however, have an FlhF protein with a signal recognition particle (SRP) domain and GTPase activity whose role is still enigmatic. Previous studies and observations have found that in a C. jejuni strain lacking FlhF, loss of motility and an aflagellate phenotype are observed. However under selective pressure, C. jejuni ΔflhF is able to revert to have partial motility. These pseudorevertants have an increasing unipolar phenotype when transitioning from exponential to stationary growth phase and have 50-70% of the wild-type motility. These pseudorevertant strains have provided a novel way of studying the FlhF protein. Sequencing of the pseudorevertants identified mutations in the fliF and fliG genes. FliF forms an oligomeric structure called the MS ring, which sits at the base of the flagella structure and surrounds the T3SS. FliG interacts with FliF and forms part of the C ring, placed below the MS ring. Analyses of these mutations suggest that they cause changes that make the structure more rigid, potentially forcing an interaction between the rings and T3SS. In the pseudorevertants, unlike the ΔflhF strain, transcription levels of σ54 and σ28 genes reach wild-type levels. The data in this thesis suggest that the role of FlhF is to activate a conformational change within the flagella base, locking it into the correct position and thereby creating the signal for the FlgSR cascade and σ54 transcription. The global analysis conducted in this thesis also provides many other insights into the C. jejuni flagellar cascade.