Influence of phosphate on aluminum tolerance inPseudomonas fluorescens

Abstract

When grown in a minimal mineral medium containing 0.64 mM phosphate, Pseudomonas fluorescens attained a cellular yield comparable to that observed in a similar medium with 64 mM phosphate. However, the inclusion of aluminum in these two media evoked disparate responses to aluminium stress. In the latter culture, aluminum was immobilized as a gelatinous lipid-rich residue (Appanna et al., FEMS Microbiol. (1994) 119, 295–302), while in the former medium the trivalent metal was sequestered in soluble metabolite(s) localized in the spent fluid. In the medium with 0.64 mM phosphate, the cellular yield decreased by 10–40% in the presence of 3–15 mM aluminum. Citrate, the sole source of carbon to which the metal was complexed, was completely utilized and no significant change in exocellular protein or carbohydrate was evident. While only a trace amount of aluminum was recorded in the soluble cellular fraction, only 11% of the test metal was immobilized as a lipid residue. However, most of the metal was sequestered in metabolite(s) localized in the spent fluid. It appears that mechanism(s) initiated by the microbe to achieve aluminum homeostasis is dependent on the phosphate concentration in the medium.