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

Department of Microbiology, Swiss Federal Institute of Environmental Science and Technology (EAWAG) and Swiss Federal Institute of Technology (ETH), Überlandstrasse 133, CH-8600 Dübendorf, Switzerland
Laboratory for Electron Microscopy, Swiss Federal Institute of Technology (ETH), CH-8092 Zürich, Switzerland
Department of Pathology, University Hospital Zürich, CH-8091 Zürich, Switzerland

Author for correspondence: Thomas Egli. Tel: + 41 1 823 5158. Fax: + 41 1 823 5547. e-mail: egli@eawag.ch

ABSTRACT

Summary: 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 transport of EDTA into whole cells was investigated. EDTA uptake was found to be dependent on speciation: free EDTA and metal-EDTA complexes with low stability constants were readily taken up, whereas those with stability constants higher than 10¹⁶ were not transported. In EDTA-grown cells, initial transport rates of CaEDTA showed substrate-saturation kinetics with a high apparent affinity for CaEDTA (affinity constant K_t = 0.39 µM). Several uncouplers had an inhibitory effect on CaEDTA transport. CaEDTA uptake was also significantly reduced in the presence of an inhibitor of ATPase and the ionophore nigericin, which dissipates the proton gradient. Valinomycin, however, which affects the electrical potential, had little effect on uptake, indicating that EDTA transport is probably driven by the proton gradient. Of various structurally related compounds tested only Ca²⁺-complexed diethylenetriaminepentaacetate (CaDTPA) competitively inhibited CaEDTA transport. Uptake in fumarate-grown cells was low compared to that measured in EDTA-grown bacteria. These results strongly suggest that the first step in EDTA degradation by strain DSM 9103 consists of transport by an inducible energy-dependent carrier. Uptake experiments with ⁴⁵CA²⁺ in the presence and absence of EDTA indicated that Ca²⁺ is transported together with EDTA into the cells. In addition, these transport studies and electron-dispersive X-ray analysis of electron-dense intracellular bodies present in EDTA-grown cells suggest that two mechanisms acting simultaneously allow the cells to cope with the large amounts of metal ions taken up together with EDTA. In one mechanism the metal ions are excreted, in the other they are inactivated intracellularly in polyphosphate granules.

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