MUTANT OF SALMONELLA TYPHIMURIUM DEFICIENT IN THE CARBON DIOXIDE-FIXING ENZYME PHOSPHOENOLPYRUVIC CARBOXYLASE

Abstract

Theodore, Theodore S. (University of Pittsburgh, Pittsburgh, Pa.), and Ellis Englesberg . Mutant of Salmonella typhimurium deficient in the carbon dioxide-fixing enzyme phosphoenolpyruvic carboxylase. J. Bacteriol. 88: 946–955. 1964.—Resting cells of Salmonella typhimurium wild type (C + dg s ) and the C - dg s mutant characterized by impaired glucose and glycerol metabolism are able to oxidize Krebs cycle intermediates to the same extent. The wild type oxidized glucose and pyruvate “completely,” and the mutant oxidized these substrates at a reduced rate and incompletely, with the accumulation of acetate. Resting cells of the wild type in the presence of NaHCO 3 - C 14 and glucose incorporated 11 times more CO 2 than did similar suspensions of the mutant. Extracts prepared from cells previously grown in a mineral glucose supplemented medium revealed that the mutant was deficient in the CO 2 -fixing enzyme phosphoenolpyruvic carboxylase (PEP carboxylase). This enzyme was found to be present in the wild-type extracts. It catalyzes the formation of oxaloacetate from phosphoenolpyruvate and CO 2 in the presence of Mn ++ or Mg ++ . No added nucleotides are required for its activity. Since only low levels of phosphoenolpyruvic carboxykinase activity are present in extracts prepared from both kinds of cells grown in a mineral glucose supplemented medium, and perhaps only trace amounts of the malic enzyme, phosphoenolpyruvic carboxytransphosphorylase, and of the enzyme requiring pyruvate, CO 2 , and adenosine triphosphate are present, it was concluded that PEP carboxylase is required for CO 2 , fixation in this organism. The loss of this enzyme prevents the growth of the mutant in a mineral-glucose or mineral-glycerol medium, and results in the incomplete oxidation of glucose and pyruvate with the accumulation of acetate. This is the first demonstration of the essential role of this particular enzyme in CO 2 fixation in chemoorganotrophs.