INFLUENCE OF PHOSPHATE ON ALUMINUM TOLERANCE IN PSEUDOMONAS-FLUORESCENS

When grown in a minimal mineral medium containing 0.64 mM phosphate, P seudomonas fluorescens attained a cellular yield comparable to that ob served in a similar medium with 64 mM phosphate. However, the inclusio n of aluminum in these two media evoked disparate responses to aluminu m stress. In the latter culture, aluminum was immobilized as a gelatin ous lipid-rich residue (Appanna et al., FEMS Microbiol. (1994) 119, 29 5-302), 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 wh ich the metal was complexed, was completely utilized and no significan t change in exocellular protein or carbohydrate was evident. While onl y a trace amount of aluminum was recorded in the soluble cellular frac tion, only 11% of the test metal was immobilized as a lipid residue. H owever, most of the metal was sequestered in metabolite(s) localized i n the spent fluid. It appears that mechanism(s) initiated by the micro be to achieve aluminum homeostasis is dependent on the phosphate conce ntration in the medium.