(Webinar) For Whom the Cell Tolls: Response of Bacterial Growth to Osmotic Shock

Enrique Rojas, a postdoctoral fellow in KC Huang's lab at Stanford University will be presenting his discoveries about the differing effects of osmotic pressure on Escherichia coli and Bacillus subtilis and the implications for cell growth. ----------------------------- The peptidoglycan cell wall is a universal feature of bacteria that determines their shape, their effect on the human immune system, and their susceptibility to many of our front-line antibiotics. Therefore, it is essential to understand this structure's physiology. Here, Dr. Rojas examines the fundamental biomechanical and biochemical processes that drive cell-wall expansion during cell growth for three different bacteria. Using single-cell, time-lapse microscopy and microfluidic-based cell culture, he demonstrates that, contrary to a long-standing hypothesis, osmotic pressure plays a relatively minor role during cell-wall expansion in the Gram-negative bacterium Escherichia coli, and that growth is robust to changes in osmotic pressure. This may be an important adaptation for an enteric bacterium, which regularly faces drastic changes in its osmotic environment during entry and exit from the intestine. On the other hand, he shows that the growth rate of the Gram-positive bacterium Bacillus subtilis is very sensitive to osmotic pressure. Therefore, Dr. Rojas shows that there at least two mechanisms for cell-wall expansion in bacteria, one in which pressure is a critical factor and one in which it is not, and furthermore that these two mechanisms may have co-evolved with the ultrastructure of the cell-wall. Finally, Dr. Rojas discusses the computational model he is developing that simulates the cell growth behavior.