Manganese acquisition by Lactobacillus plantarum

Abstract

L. plantarum has an unusually high Mn(II) requirement for growth and accumulated > 30 mM intracellular Mn(II). The acquisition of Mn(II) by L. plantarum occurred via a specific active transport system powered by the transmembrane proton gradient. The Mn(II) uptake system has a Km of 0.2 .mu.M and a Vmax of 24 nmol/mg of protein per min. Above a medium Mn(II) concentration of 200 .mu.M, the intracellular Mn(II) level was independent of the medium Mn(II) and unresponsive to O2 stresses but was reduced by PO42- limitation. At a pH of 5.5, citrate, isocitrate and cis-aconitate effectively promoted Mn(II) uptake, although measurable levels of 1,5-[14C]citrate were not accumulated. When cells were presented with equimolar Mn(II) and Cd(II), Cd(II) was preferentially taken up by the Mn(II) transport system. Both Mn(II) and Cd(II) uptake were greatly increased by Mn(II) starvation. Mn(II) uptake by Mn(II)-starved cells was subject to a negative feedback regulatory mechanism functioning < 1 min after exposure of the cells to Mn(II) and independent of protein synthesis. When presented with a relatively large amount of exogenous Mn(II), Mn(II)-starved cells exhibited a measurable efflux of their internal Mn(II), but the rate was only a small fraction of the maximal Mn(II) uptake rate.