Gallium toxicity and adaptation in Pseudomonas fluorescens

Abstract

When cultured in a defined citrate medium supplemented with 1 mM gallium (III) Pseudomonas fluorescens ATCC 13525 experienced a lag phase of 40 h with no apparent diminution in cellular yield. Following initial uptake of the metal-ligand complex, gallium was secreted in the spent fluid. This lag phase was abolished either by inoculating the medium with gallium adapted cells or by inclusion of iron (III) (20 microM) in the growth medium. In the culture enriched with both gallium and iron (III), X-ray fluorescence spectra revealed a gradual decrease of gallium from the spent fluid as growth progressed. In a phosphate deficient medium, no cellular multiplication was observed in the presence of gallium. The inhibitory influence mediated by the trivalent metal was reversed by the addition of (20 microM) iron (III). Although bacterial growth was accompanied by an initial decrease in exocellular gallium, a marked increment in the concentration of this metal was observed in the spent fluid at stationary phase of growth. Citrate was not detected in the exocellular fluid at cessation of bacterial multiplication. Electrophoretic analyses revealed numerous variations in the cytoplasmic protein profiles of the control and metal stressed cells. Gallium induced the syntheses of polypeptides with apparent molecular masses of 89 kDa, 50 kDa, 39 kDa, 26 kDa and 12 kDa.