Citrate utilization by Escherichia coli: plasmid- and chromosome-encoded systems.

摘要: Citrate utilization plasmids have previously been identified in atypical Escherichia coli isolates. A different citrate-utilizing (Cit+) variant of E. K-12 arose as a consequence two chromosomal mutations (B. G. Hall, J. Bacteriol. 151:269-273, 1982). The processes controlling the transport citrate both Cit+ mutant and plasmid system were studied. Both systems found to be inducible growth experiments. In assays with whole cells, citrate-grown cells accumulated [1,5-14C]citrate at three times rate uninduced cells. Only Vmax was affected by induction, Km for remained 67 microM strain 120 plasmid-conferred system. There no detectable accumulation radioactivity [6-14C]citrate, because rapid metabolism release 14CO2. Energy-dependent membrane vesicles obtained from chromosome-conferred systems. vesicle inhibited valinomycin carbonyl cyanide m-chloro-phenylhydrazone but not nigericin monensin. contrast resistant Hg2+ showed identical kinetics [6-14C]citrate. H+ appeared important membranes. Monovalent cations such Na+ K+, divalent Mg2+ Mn2+, anions PO4(3-), SO4(2-), NO3- required. differed inhibition analogs.