PHYSIOLOGY AND MORPHOLOGY OF LEGIONELLA-PNEUMOPHILA IN CONTINUOUS CULTURE AT LOW OXYGEN CONCENTRATION

Two strains of Legionella pneumophila serogroup 1 monoclonal subgroup Pontiac were grown for the first time in continuous culture using a chemically defined medium. The influence of temperature on physiology and morphology was investigated by fixing the growth rate (equal to the dilution rate, D) at 0.08 h-1 and controlling the pH and dissolved oxygen concentration of the culture. Serine provided the principal source of carbon and energy but growth was limited by tyrosine. The bacterium behaved as a microaerophile in this medium, with maximal growth occurring at 0.31 (mg O2) l-1 (equivalent to a dissolved oxygen tension of 4 % (v/v) air saturation at 30-degrees-C). The cultures consisted of flagellated, short rods at 24-degrees-C, but exhibited an increased level of pleomorphism and the loss of flagella as the temperature was increased to 37-degrees-C. The presence of intracellular granules was noted, and their abundance was temperature-dependent. Polyhydroxybutyrate was present in L. pneumophila, and the proportion of the cell dry weight that it accounted for varied with temperature, being maximal at 24-degrees-C. The ratio of saturated to unsaturated fatty acids in the cells decreased as the temperature was reduced towards 24-degrees-C, so as to maintain membrane fluidity at low growth temperature.