Anhydrobiotes

Desiccation tolerant species may exhibit little or no metabolic activity depending upon the extent of dehydration. In this anhydrobiotic or ametabolic state we are concerned not with metabolic perturbation but with the stability of organelles, membranes and macromolecules in a dehydrated state. However, in the initial period of rehydration, the passage to a metabolically active state poses particular problems if metabolic mayhem is to be avoided. 

Ripening seeds, except where they are enclosed in fleshy fruit, lose water until their water content is in equilibrium with atmospheric humidity and at this stage they contain 5-20% water. The water contents of some seeds can be reduced still further with no adverse effects on viability, rather this can enhance their survival in the dried state (Roberts, 1973). The longevity of seeds in this anhydrobiotic state can be prodigious, lasting for several hundred years (Priestley Posthumus, 1982). 

However, some microorganisms, the so-called anhydrobiotes, are able to deal better with a lack of water. One of their strategies for survival is the accumulation of non-reducing sugars (disaccharides) which replace the lost water during dry periods and can, for example, stabilise membrane structures, even when water is not present. 

Crowe, J.H., and L.M. Crowe (1992). Membrane integrity in anhydrobiotic organisms toward a mechanism for stabilizing dry cells. In Water and Life, pp. 87-103, ed. G.N. Somero, C.B. Osmond, and C.L. Bolis. Berlin Springer-Verlag. 

Fig. 12.7. Glass in anhydrobiotic larvae and their recovery after heat treatments, (a) DSC thermograms for slowly and quickly dehydrated larvae, (b) Dependence of the recovery rate after rehydration on exposure to high temperatures in slowly (,filled symbols) and quickly (open symbols) dehydrated larvae. Circles and triangles show recovery after exposure to high temperature for 5 min and 1 h, respectively. Data from [73]...

Crowe JH, Crowe LM, Chapman D (1984) Preservation of membranes in anhydrobiotic organisms. The role of trehalose. Science 223 701-703... 

Metabolic activity has been measured in the desiccated state of seeds, spores, and anhydrobiotic organisms such as Artemia (Crowe and Clegg, 1973, 1978 Leopold, 1986). The threshold for metaboUc activity is generally 0.2—0.3 h. 

Biological systems are, by definition, multicomponent systems. One should keep in mind the difficulties of constructing molecular level pictures that satisfactorily describe systems such as a protein in a reverse micelle or a protein in a concentrated aqueous salt solution, which are certainly much simpler than anhydrobiotic organisms, for example. It is not clear to what extent the water of the hydration shell can be replaced by a third component (e.g., lipid) or what effect such replacement has on protein or enzyme properties. 

Connectivity has a central role in biochemistry and biology, and one imagines that the percolation model, with its focus on connectivity, should have wide application. Percolative behavior is to be expected for the coordinate functioning of systems of proteins in metabolic pathways, for functional interactions between proteins embedded in a membrane, for the interactions between domains in the folding of a polypeptide, or for the onset of function in anhydrobiotic organisms, seeds, and spores. 

Faurby, S., Jonsson, K.I., Rebecchi, L., Punch, P. (2008). Variation and anhydrobiotic survival of two eutardigrade morphospecies a story of cryptic species and their dispersal. Journal of Zoology 275,139-145. 

Neumaim, S., Reuner, A., Briimmer, F., Schill, R.O. (2009). DNA damage in storage cells of anhydrobiotic tardig -ades. Comparative Biochemistry and Physiology Part A Molecular and Integrative Physiology 153,425-429. 

Rebecchi, L., Guidetti, R., Borsari, S., Altiero, T., Bertolani, R. (2006). Dynamics of longterm anhydrobiotic survival of lichen-dwelling tardigrades. Hydrobiologia 558, 23-30. 

Meng, X. C., Stanton, C., Fitzgerald, G., Daly, G., Ross, R. P. (2008). Anhydrobiotics the challenges of drying probiotic cultures. Food Chemistry, 106, 1406-1416. 

Tunnacliffe, A., de Castro, A.G., and Manzanera, M. 2001. Anhydrobiotic engineering of bacterial and mammalian cells Is intracellular trehalose sufficient Cryobiology A3 1A- 31. 

Sun, WQ. and Leopold, A.C., Cytoplasmic vitrification and survival of anhydrobiotic organisms, Compar. Biochem. Physiol, 117A, 327,1997. 

Buitink, J. and Leprince, O., Glass formation in plant anhydrobiotes survival in the dry state. Cryobiology, 48, 215, 2004. 

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