Transport of EDTA into cells of the EDTA-degrading bacterial strain DSM 9103

In the bacterial strain DSM 9103, which is able to grow with the complexing agent EDTA as the sole source of carbon, nitrogen and energy, the transpor t of EDTA into whole cells was investigated. EDTA uptake was found to be de pendent on speciation: free EDTA and metal-EDTA complexes with low stabilit y constants were readily taken up, whereas those with stability constants h igher than 10(16) were not transported. In EDTA-grown cells, initial transp ort rates of CaEDTA showed substrate-saturation kinetics with a high appare nt affinity for CaEDTA (affinity constant K-t = 0.39 mu M). Several uncoupl ers had an inhibitory effect on CaEDTA transport. CaEDTA uptake was also si gnificantly reduced in the presence of an inhibitor of ATPase and the ionop hore nigericin, which dissipates the proton gradient. Valinomycin, however, which affects the electrical potential, had little effect on uptake, indic ating that EDTA transport is probably driven by the proton gradient. Of var ious structurally related compounds tested only Ca2+-complexed diethylenetr iaminepentaacetate (CaDTPA) competitively inhibited CaEDTA transport. Uptak e in fumarate-grown cells was low compared to that measured in EDTA-grown b acteria. These results strongly suggest that the first step in EDTA degrada tion by strain DSM 9103 consists of transport by an inducible energy-depend ent carrier. Uptake experiments with Ca-45(2+) in the presence and absence of EDTA indicated that Ca2+ is transported together with EDTA into the cell s. In addition, these transport studies and electron-dispersive X-ray analy sis of electron-dense intracellular bodies present in EDTA-grown cells sugg est that two mechanisms acting simultaneously allow the cells to cope with the large amounts of metal ions taken up together with EDTA. In one mechani sm the metal ions are excreted, in the other they are inactivated intracell ularly in polyphosphate granules.