*********************************
There is now a CONTENT FREEZE for Mercury while we switch to a new platform. It began on Friday, March 10 at 6pm and will end on Wednesday, March 15 at noon. No new content can be created during this time, but all material in the system as of the beginning of the freeze will be migrated to the new platform, including users and groups. Functionally the new site is identical to the old one. webteam@gatech.edu
*********************************
shaun.ashley@physics.gatech.edu
Summary Sentence: School of Physics, Soft Condensed Matter & Physics of Living Systems Seminar, Dr. Enrique Rojas, New York University
Full Summary: No summary paragraph submitted.
Enrique RojasI will discuss the adaptive strategies that diverse microbes, including prokaryotic and eukaryotic organisms, use to cope with their mechanical environment and with the mechanical constraints imposed on them by evolution. First, it is well understood that the peptidoglycan cell wall is an essential mechanical structure for bacteria. In Gram-negative bacteria, it is widely believed that the outer membrane simply provides an additional permeability barrier. Conversely, I will show that the outer membrane is at least as stiff as the cell wall and plays a critical role in protecting bacteria from mechanical insults, revising our textbook understanding of bacterial mechanics. I will discuss ongoing efforts to dissect the biochemical and structural basis for the outer membrane's mechanical properties. Second, it is well established that fungal and protistan hyphae use turgor pressure to drive cell-wall expansion during cell growth. I will show how this mechanism, combined with an evolutionary selection for fast growth, provides a tight developmental constraint on the range of possible cell shapes. Using computational modeling, I will demonstrate that this constraint takes the form of a "tipping-point catastrophe" often seen in dynamical systems theory. These examples elucidate how the interplay of evolution and physics conspire to determine the ultrastructure and shape of microbial cells.
