X-Message-Number: 15396
Date: Sat, 20 Jan 2001 10:15:36 -0800 (PST)
From: Doug Skrecky <>
Subject: desiccation tolerance

Title
  Desiccation tolerance of prokaryotes. [Review] [433 refs]
Source
  Microbiological Reviews.  58(4):755-805, 1994 Dec.
Abstract
  The removal of cell-bound water through air drying and the addition of water
  to air-dried cells are forces that have played a pivotal role in the
  evolution of the prokaryotes. In bacterial cells that have been subjected to
  air drying, the evaporation of free cytoplasmic water (Vf) can be
  instantaneous, and an equilibrium between cell-bound water (Vb) and the
  environmental water (vapor) potential (psi wv) may be achieved rapidly. In
  the air-dried state some bacteria survive only for seconds whereas others can
  tolerate desiccation for thousands, perhaps millions, of
  years. The desiccated (anhydrobiotic) cell is characterized by its singular
  lack of water--with contents as low as 0.02 g of H2O g (dry weight)-1. At
  these levels the monolayer coverage by water of macromolecules, including DNA
  and proteins, is disturbed. As a consequence the mechanisms that confer
  desiccation tolerance upon air-dried bacteria are markedly
  different from those, such as the mechanism of preferential exclusion of
  compatible solutes, that preserve the integrity of salt-, osmotically, and
  freeze-thaw-stressed cells. Desiccation tolerance reflects a
  complex array of interactions at the structural, physiological, and molecular
  levels. Many of the mechanisms remain cryptic, but it is clear that they
  involve interactions, such as those between proteins and co-solvents, that
  derive from the unique properties of the water molecule. A water replacement
  hypothesis accounts for how the nonreducing disaccharides trehalose and
  sucrose preserve the integrity of membranes and proteins. Nevertheless, we
  have virtually no insight into the state of the cytoplasm of an air-dried
  cell. There is no evidence for any obvious adaptations of proteins that can
  counter the effects of air drying or for the occurrence of any proteins that
  provide a direct and a tangible contribution to cell stability. Among the
  prokaryotes that can exist as anhydrobiotic cells, the cyanobacteria have a
  marked capacity to do so. One form, Nostoc commune, encompasses a number of
  the features that appear to be critical to the withstanding of a long-term
  water deficit, including the elaboration of a conspicuous extracellular
  glycan, synthesis of abundant UV-absorbing pigments, and maintenance of
  protein stability and structural integrity. There are indications of a
  growing technology for air-dried cells and enzymes. Paradoxically,
  desiccation tolerance of bacteria has virtually been ignored
  for the past quarter century. The present review considers what is known, and
  what is not known, about desiccation, a phenomenon that
  impinges upon every facet of the distributions and activities of prokaryotic
  cells. [References: 433]

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