The Effect of the Growth Medium on the Composition and Metal Binding Behaviour of the Extracellular Polymeric Material of a Metal-AccumulatingCitrobactersp

Cells of a heavy metal-accumulating Citrobacter sp. appeared electron-opaque under the electron microscope when pre-grown in medium containing lactose and inorganic phosphate as the respective carbon and phosphorus sources, compared to cells supplied with glycerol and glycerol 2-phosphate. This was attributable to a greater proportion of bound metal cations, as analysed using proton induced X-ray emission analysis of extracted extracellular polymeric material (EPM). This was associated with a greater content of EPM-associated phosphorus and also an enhanced activity of isolated EPM to accumulate uranyl ion, to 23% of the polymer dry weight. EPM from glycerol 2-phosphate-grown cells, analysed using 31P nuclear magnetic resonance spectroscopy, gave several major phosphorus resonances between −1 and 2 ppm, in accordance with published spectra for enterobacterial lipopolysaccharide. Addition of Cd2+ promoted a shift downfield of the P resonances to a new, common, resonance at 3 ppm which was similar to that o...