The Physical State of Water in Dormant Bacteria
Creators: DeLay, Michael
Publisher: name: Columbia University
Year: 2018
Subjects: Biophysics
Bacteria
Bacterial spores
Water
Biology

description: Anomalous behaviour of water confined in nanoscale gaps influences many biological and technological processes.  However, due to the small size of confining structures, it is historically difficult to manipulate and study water’s dimension-dependent transport character.  Experimental studies of nanoconfined water are generally limited to artificial test structures, and/or single-file channels, and so transport behavior of biologically nanoconfined water remains elusive.  We utilize poroelastic bacterial spores coated onto a nanomechanical sensor to probe photo-thermal evaporative relaxation in a biological setting and report viscous water, 7 orders of magnitude larger than that of bulk liquid, and via thermodynamic investigations reveal an activation energy close to ice.  Overall, these experiments characterize transport behaviour of nanoconfined water in vivo, and highlight the dramatic effects of nanoscale confinement on water that could impact myriad natural and synthetic processes.
      	Following from this work, a hypothesis is pursued in which the bacterial lifecycle is intimately connected with transitions in the physical structure of the internal water.  We expand an initial idea proposed in Science, 1960 by J.C. Lewis, N.S. Snell and H.K. Burr that the low water content of the spore core is accomplished through compressive contraction during development3. During sporulation, the genetic material is packaged with chelating chemicals within a special water-responsive, layered coating that electrostatically pulls the water out of the core. Together, these agents produce the extremely dehydrated, hydraulically tensioned, and stable spore-phase organism.  During germinative re-awakening, an event lacking a complete mechanistic theory of sensation, the core is rehydrated and the organism subsequently reanimated.  This work’s findings regarding the spore’s physically restrained but exchangeable water support the idea that the physical state of the water contributes significantly to tensioning the organisms into a ‘charged’ but dormant configuration.  This dormant but spring-loaded phase of the bacterial lifecycle is subject to awakening by agents (nutrient or otherwise) which disrupt surface tension including amino acids, salts, surfactants, and hydrostatic pressures.  In the least, it must be acknowledged that the slowed water observed herein enforces slowed biochemistry and thus dormancy. 
      Taken together we present a picture where internal spore water, even that which is exchanged with the external environment, is nanoconfined and slowed under tremendous tension (negative pressure).  The mechanism governing this slow water appears to be unlike that any previously described, the majority of which are typically based upon crystalline surfaces, the likes of which are not found in the spore.  We consider that the spore water structure itself participates, in certain environments, in the signaling chain of the organism through stabilizing a delicately balanced and highly tensioned architecture.  Presently we are working toward testing the hypothesis and expanding our understanding with new methods, including additional structural mutants and expanded biophysical techniques.