Physical mechanisms for bacterial cell shape determination

Kc Huang
Biochemistry and Electrical Engineering, Stanford University

(October 11, 2010 2:30 PM - 3:30 PM)

Physical mechanisms for bacterial cell shape determination

Abstract

Bacterial cells come in a wide variety of shapes and sizes, with the peptidoglycan cell wall as the primary stress-bearing structure that dictates cell shape. In recent years, cell shape has been shown to play a critical role in regulating many important biological functions including attachment, dispersal, motility, polar differentiation, predation, and cellular differentiation. How much control does a cell have over its shape, and can we tap into control mechanisms to synthetically engineer new morphologies? Though many molecular details of the composition and assembly of the cell wall components are known, how the peptidoglycan network organizes to give the cell shape during normal growth, and how it reorganizes in response to damage or environmental forces have been relatively unexplored. We have introduced a quantitative mechanical model of the bacterial cell wall that predicts the response of cell shape to peptidoglycan damage in the rod-shaped Gram-negative bacterium Escherichia coli. We have verified some of our predictions regarding morphological response to antibiotics using time-lapse imaging, suggesting that mechanical modelling of the cell wall can inform our understanding of cellular physiology. Our simulations based on our physical model also suggest a surprising robustness of cell shape to damage, allowing cells to grow and maintain their shape even under conditions that limit crosslinking. Our current research focuses on identifying the molecular factors responsible for cell shape determination and characterizing their phylogenetic diversity. In particular, we demonstrate that a small set of physical rules determines the cell's shape and the ability of the cell to maintain that shape, and we have used these rules to systematically alter the dimensions of rod-shaped bacteria. Our work has shown that many common bacterial cell shapes can be realized within both our model and in experiments via simple spatial patterning of the cytoplasm and cell wall, suggesting that subtle patterning changes could underlie the great diversity of shapes observed in the bacterial kingdom.