CULTIVATION OF HYPERTHERMOPHILIC ARCHAEA CAPILLARY TUBES RESULTING INIMPROVED PRESERVATION OF FINE-STRUCTURES

A method for cultivating hyperthermophilic archaea that results in ver y high cell densities and in improved structural preservation of the c ells is described. Cellulose capillary tubes, originally introduced as containers for embedding for electron microscopy, were filled with ce lls, closed at both ends, and put into sterile culture medium. Within these capillaries, which serve as ultrafiltration chambers, cells coul d be cultivated to much higher cell densities than in regular cultures . The capillaries containing cells were processed for ultrathin-sectio ning by fixation, freeze-substitution, and embedding. Using this culti vation procedure, centrifugation, which may destroy sensitive structur al components, could be avoided, and the cells of hyperthermophilic ar chaea were well-preserved. These undisturbed cells revealed the follow ing new structural features: (1) a high number of tubules in ultrathin -sections, indicating a well-preserved network of Pyrodictium cells an d tubules; (2) ''ultraflat areas'' of Pyrodictium cells, with the two membranes being in direct contact and, at some places, bulging out, fo rming evaginations; (3) novel cell-to-cell connections between Thermop roteus cells and, similarly, between Pyrobaculum cells; and (4) a surf ace coat on Pyrobaculum aerophilum cells. The cultivation procedure of fers distinct advantages over conventional techniques and might be app licable for improved electron microscopy of other sensitive microorgan isms.