Building the bacterial flagellum: coordinating regulation, dynamic assembly, and function

SUMMARYBacterial flagella are remarkable rotary machines that enable motility, environmental sensing, and host interaction. In this review, we discuss recent advances in understanding the structure, assembly, and regulation of the flagellum in <i>Salmonella enterica</i>, emphasizing both common principles and distinctive features across bacteria. We discuss the hierarchical gene regulation, the dynamic mechanics of the motor, and recent structural insights into the flagellar core components. We also reflect on the legacy of Howard Berg, whose foundational work in <i>Escherichia coli</i> shaped much of what we know about bacterial locomotion in Gammaproteobacteria. His contributions, from flagellar rotation to chemotaxis and motor dynamics, transformed the field and continue to inspire current research into one of nature's most intricate nanomachines. Finally, we highlight open questions that place bacterial motility within the broader context of cellular processes and call for detailed single-cell observations.