Abstract
The flagellum is a rotary motor that enables bacteria to swim in liquids and swarm over surfaces. Numerous global regulators control flagellar assembly in response to cellular and environmental factors. Previous studies have also shown that flagellar assembly is affected by the growth-rate of the cell. However, a systematic study has not yet been described under controlled growth conditions. Here, we investigated the effect of growth rate on flagellar assembly in Escherichia coli using steady-state chemostat cultures where we could precisely control the cell growth-rate. Our results demonstrate that flagellar abundance correlates with growth rate, where faster growing cells produce more flagella. They also demonstrate that this growth-rate dependent control occurs through the expression of the flagellar master regulator, FlhD4C2. Collectively, our results demonstrate that motility is intimately coupled to the growth-rate of the cell.
Highlights
The flagellum is a rotary motor that enables bacteria to swim in liquids, swarm over surfaces and aid attachment to surfaces[1]
We investigated the extent to which the growth-rate of the cell controls flagellar formation in E. coli in steady-state chemostat cultures, where we can precisely control the growth-rate of the cell[8]
To count the number of flagella in the cell, we utilized a strain expressing a functional fusion of FliM, which forms the inner C-ring of the flagellum, to the yellow fluorescent protein variant, YPet[11]
Summary
The flagellum is a rotary motor that enables bacteria to swim in liquids, swarm over surfaces and aid attachment to surfaces[1]. Numerous regulators have been shown to control flagellar gene expression in E. coli[4] Key among these is the flhDC operon, encoding the FlhD4C2 transcriptional regulator[5,6]. FlhDC expression is known to vary during cell growth, where expression is greatest during mid-log phase[7] These results suggest that motility is coupled to the growth-rate of the cell. Our data suggest that this growth-rate dependent control occurs via changes in the expression of the flagellar master regulator, FlhD4C2. We conclude that this intimate relationship between growth-rate and flagellar abundance indicates that cells exploit flagella for more than just foraging for food
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