Interaction of sn-glycerol 3-phosphorothioate with Escherichia coli: effect on cell growth and metabolism

Abstract

sn-Glycerol 3-phosphorothioate was found to be bacteriocidal to strains of Escherichia coli which have a functional sn-glycerol 3-phosphate transport system. This effect was manifest in strains 7 and 8, which are constitutive mutants for the utilization and transport of sn-glycerol 3-phosphate (glpRc2). Strain E15, which is considered to be wild type for the glycerol phosphate functional units, was affected by the phosphorothioate analog only under conditions that are known to induce the transport system for sn-glycerol 3-phosphate. In addition, another strain of E. coli, strain 6, which is isogenic with strain E15 but has an impaired sn-glycerol 3-phosphate transport system (glpT13), was not affected by similar concentrations of sn-glycerol 3-phosphorothioate. Transport studies in which [3H]glycerol phosphate and its phosphorothioate analog were used demonstrated that the latter compound was taken up via the specific active transport system for sn-glycerol 3-phosphate; the Km values were 9 and 11 microM, respectively. The rates of macromolecular synthesis were found to be inhibited severely by sn-glycerol 3-phosphorothioate at a concentration at which sn-glycerol 3-phosphate had no effect (5 microM). At a lower concentration of the analog (0.5 microM), the rates of protein synthesis and RNA synthesis (52 and 58% below control values after 90 min, respectively) were more sensitive than the rates of DNA synthesis and cell wall synthesis (18% below control values after 3 h for DNA; transient decrease in the cell wall values after 90 min). The levels of the nucleoside triphosphates were not affected by the presence of the phospholipid precursor or its analog at a concentration of 5 microM. The phospholipid composition was significantly altered in the presence of bacteriocidal concentrations (5 microM) of sn-glycerol 3-phosphorothioate. The amount of phosphatidylglycerol in the membranes decreased from 13.5 to 3.5%. Concomitant with this decrease in phosphatidylglycerol content was a fourfold increase in the 32P content of cardiolipin (from 6.8 to 24.2%), whereas the phosphatidylethanolamine content showed only a minor reduction (8%) after 3 h. The rates of synthesis of all of the phospholipids decreased in the presence of 5 microM sn-glycerol 3-phosphorothioate, with the most significant effects observed for phosphatidylglycerol (63% after 3 h). Phosphatidylglycerol showed increased rates of turnover after 90 min (21%) and 3 h (11%), with concomitant increases in the levels of cardiolipin of more than twofold.(ABSTRACT TRUNCATED AT 400 WORDS)