Glucose and glutamate metabolism ofLegionella pneumophila

Abstract

Two serotype 1 strains ofLegionella pneumophila, Phildelphia 2 and Bellingham, were tested for their ability to metabolize five common substrates by measuring14CO2 released and14C-carbon incorporated into macromolecules. No major differences were noted between the two strains or preparations grown in the yolk sac of chick embryos or agar-broth diphasic medium, following 2 or 14 pasaages on agar. Glutamate was the most actively metabolized substrate, followed by glutamine. Acetate, glucose, and succinate were utilized at much more moderate rates. Changes in cell density and substrate concentration altered the channeling of glutamate and glucose into CO2 and macromolecules. Specific CO2 felease from glutamate was greatest at low cell density and high substrate concentration, while carbon incorporation was increased at high substrate concentration. A reciprocal relationship was noted with glucose: the proportion of carbon incorporation was enhanced at low substrate concentration, but CO2 release paralleled increases in substrate concentration. The pH optimum for glutamate carbon incorporation and CO2 release was 5.5 and 6.1, respectively, but 25% of both activities were retained at pH 3.1. CO2 release from glucose was maximal at pH 7.5 with negligible activity at pH 3.1. Pathways of glucose metabolism were explored by employing glucose, glucose-1-phosphate, and glucose-6-phosphate labeled in various carbon positions. The glycolytic pathway appeared to play a lesser role than the pentose phosphate and/or Entner-Doudoroff pathways. Glucose-1-phosphate was metabolized at a much higher rate than glucose or glucose-6-phosphate. We conclude that glutamate is utilized primarily as an energy source while glucose may serve as an important metabolite for the nutrition ofL. pneumophila.