Simbios Talk by KC Huang, Stanford University, June 9, 2010

Title: The Structure and Maintenance of the Bacterial Cell Envelope

KC Huang*,a Julie Theriotb and Wah Chiuc
a, Department of Bioengineering, Stanford University, Stanford, CA, 94304. b, Department of Biochemistry, Stanford University, Stanford, CA, 94304.
c, Director of Center for Macromolecular Imaging, Baylor University, Houston, TX 77030.

The bacterial cell envelope consists of a cytoplasmic membrane surrounded by a cell wall and, for Gram-negative bacteria, a second outer membrane. The mechanical and fluid properties vary dramatically between these layers. I will describe how our DBP will address this complex combination of structures using experimental and computational techniques. The peptidoglycan cell wall is 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? We have introduced a quantitative biophysical model of bacterial cell-wall growth that demonstrates that spatial patterning is necessary for cell-shape maintenance. Our simulations also predict a strong dependence of size on the molecular details of the inserted material, and we have verified experimentally that modifications to the insertion machinery can modulate the size of E. coli cells in a continuous fashion. In addition, we have demonstrated that the mobility of the outer membrane is slaved to the growth of the cell wall, and that random insertion of material can produce patterns of outer membrane lipopolysaccharides and proteins. Finally, I will describe our plan to map the structure of the envelope at high resolution using Cryo-EM, focusing on the reorganization caused by phage infection. Our approach combines structural and cytological approaches with biophysical modelling to uncover mechanisms by which bacterial cells regulate their shape and maintain their integrity.