School of Physics, Soft Condensed Matter & Physics of Living Systems Seminar, Dr. Enrique Rojas, New York University

I 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.