Applied Microbiology

Biography

Biography: Alexander Rapoport

Abstract

Anhydrobiosis is unique state of live organisms which is linked with temporary reversible delay of their metabolism as the result of strong desiccation in extreme conditions of the environment. The discovery of this amazing phenomenon was made by great Dutch naturalist Anthony van Leeuwenhoek in 1701. Industrial production of active dry yeasts (yeasts in the state of anhydrobiosis) has been started already at the beginning of 1940s. At the same time intensive research of intracellular mechanisms of yeast cultures transfer into the state of anhydrobiosis was begun only 30 years later – in 1970s. Studies performed during these 40 years revealed rather considerable changes in yeast cells which take place at their dehydration. Some of them are linked with the protective reactions whereas others can be very dangerous for the cells and special procedures may be necessary for the maintenance of cells viability at their subsequent restoration during rehydration/reactivation procedure. The most important changes were shown for the state of chromatin and membranes. It was concluded that condensation of chromatin at early stages of cells’ dehydration is necessary for the survival of cell and that it is one of the main intracellular protective reactions. Water hydroxyls substitution by hydroxyls from other compounds proposed by “water replacement hypothesis” promotes the maintenance of molecular organization of intracellular membranes. It was shown that besides the well-known protective substance – trehalose there are also some other compounds which can perform similar to trehalose function. One of these groups is polyhydric alcohols. The model which explains possible changes of membranes structure during dehydration and rehydration of live cells was worked out by John Crowe and Folkert Hoekstra. Main attention in this model as well as during the subsequent studies was devoted to the state and changes of membrane lipids. Recently it was received first important information on the role and possible changes of other component of biological membranes – proteins. It was revealed the difference in the reaction to desiccation of membrane proteins in the cells which differ in their resistance to dehydration. The conclusion on the main factors which are responsible for the maintenance of cells viability in the extreme conditions of the environment was formulated. The possibility to increase the resistance of sensitive yeast cultures to dehydration was found. The information on the mechanisms of yeast cells transfer into the state of anhydrobiosis is very important for further improvement of the quality of active dry yeast preparations especially in the cases when the viability and/or stability of these preparations does not quite conform to the requirements of consumers. It gives also the possibility to develop the technologies for the preservation of sensitive to dehydration cultures. At the same time it was revealed a number of additional, non-conventional applications of accumulated knowledge. One of them is linked with the use of active dry yeast preparations for the purification of waste waters from hazardous compounds and development of new active biofilters for the protection of the environment. Application of knowledge on the dehydration of yeasts in live nature led to development of a new efficient and cheap method for the obtaining of very stable preparations of immobilized microorganisms which can be used in various modern biotechnologies. An interesting model for rapid evaluation of the influence of different natural and chemical compounds upon eukaryotic cells was worked out on the basis of new knowledge. Further studies of yeast anhydrobiosis certainly will lead to new interesting discoveries in basic science which in their turn will open new approaches and possibilities for various biotechnologies.