UNSTAINED AND IN-VIVO FLUORESCENTLY STAINED BACTERIAL NUCLEOIDS AND PLASMOLYSIS OBSERVED BY A NEW SPECIMEN PREPARATION METHOD FOR HIGH-POWER LIGHT-MICROSCOPY OF METABOLICALLY ACTIVE-CELLS

Microscope slides were coated with a layer of gelatin, the thickness o f the gelatin increasing linearly along the long axis. The bacterial s uspension is applied to the dried gelatin and covered by a coverslip. The medium is absorbed by the gelatin and thus the cells applied again st the coverslip. By this method, cultures of concentrations below 10( 8) cells/ml provide statistically relevant numbers for observation wit hout prior concentration steps. It is easier to apply than the existin g methods for the observation of bacterial nucleoids by phase contrast imaging. Because the cells are maintained in growing conditions the m ethod is useful for the vital fluorescence DAPI-staining of various ba cterial species and for observations of plasmolysis and its reversal a t different physiological conditions and extracellular osmolalities. T he previously generally assumed view that the plasmolytic changes of t he cell morphology are immediate upon the hyperosmotic shock and are r apidly repaired when the cell is able to metabolize actively was confi rmed; this is in contrast to some recent claims.