How do molecular machines evolve? In situ visualisation of proteins that increase the torque of a bacterial flagellar motor.

Host: Dr Megan Bergkessel

Location: Small Lecture Theatre, MSI

Abstract

 Molecular and microbial evolution remains less well studied than that of large eukaryotes. Bacterial flagella are ideal model systems to address this gap: they are widespread and diverse (making comparative studies easy and useful), non-essential yet beneficial (enabling inactivation yet also selection), large (rendering in situ structural studies easy), and have an easily measured phenotype of rotational torque and speed. Nevertheless, the field lacks a unified narrative describing evolution of diversity in bacterial flagella: what new proteins have been recruited, and to which flagellar subtypes? What was the selective benefit of these additions? What interdependencies exist between new proteins and essential core proteins? One of the principal hurdles to tackle such questions lies in our continued inability to see these machines in situ. Electron cryo-microscopy imaging promises to remedy this. I will describe our studies using electron cryotomography and fluorescence light microscopy to understand the evolution of bacterial flagellar diversity, focusing on Campylobacter jejuni from the Campylobacterota (previously Epsilonproteobacteria). I will present work that combines innovations in sample preparation and imaging to achieve resolution sufficient to discern secondary structure elements and build a complete molecular model of the C. jejuni bacterial flagellar motor. Our findings suggest substantial interaction and interdependent co-evolution of increased motor torque with other aspects including cell shape and flagellar filament composition and provide unprecedented insights into numerous steps involved in the evolution of unusually high torque in the C. jejuni flagellar motor by protein recruitments, and the corresponding enabling and compensatory modifications of core components.

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