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Bacteria control the precise number of flagella they assemble through a conserved molecular feedback mechanism that couples transcriptional regulation to the physical assembly progress of the flagellar C-ring structure. As the C-ring grows, the ATPase FlhG is released from an inhibitory complex, dimerizes, and inactivates the master regulator FlrA, shutting down flagellar gene expression. Through stochastic simulations and analytical calculations, researchers identified a critical crossover regime between fast and slow inactivation that allows the system to achieve robustness against both intrinsic molecular fluctuations and cell-to-cell variability in protein abundance.
Why it matters
This work provides quantitative, organism-independent principles for understanding how bacteria precisely control organelle numbers, which has implications for understanding bacterial motility and potentially for synthetic biology applications requiring precise control of cellular structures. The findings also contribute to broader understanding of how biological systems use stochastic regulation to achieve robust outcomes.
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⚠️ Preprint – Noch nicht peer-reviewed
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Bacteria assemble a precise number of flagella to navigate their environment, yet the molecular mechanisms underlying this robust counting remain poorly understood. We propose that robust flagellar number control does not require a strictly conserved transcriptional gene hierarchy, but instead emerges from a conserved network motif in which transcriptional feedback is coupled to the assembly progress of the flagellar C-ring. Specifically, upon C-ring growth, the ATPase FlhG is released from a non-inhibitory FlhG-FliM complex, dimerizes, and inactivates the master regulator FlrA, shutting down early flagellar gene expression. We analyze this assembly-coupled feedback mechanism using stochastic simulations and analytical calculations, revealing a trade-off between robustness to intrinsic fluctuations and to cell-to-cell variability in regulator abundance. Only at the crossover between fast and slow inactivation regimes can robustness to both noise sources be achieved simultaneously. These results provide quantitative, organism-independent insight into flagellar number control and connect to the broader problem of stochastic regulation of absorbing-state statistics.
Source: Assembly-coupled feedback enables robust control of flagellar number