Aluminum tolerance in Pseudomonas fluorescens ATCC 13525: Involvement of a gelatinous lipid-rich residue

Abstract Pseudomonas fluorescens was found to grow in a mineral medium supplemented with up to 50 mM aluminum, complexed to citrate, the sole source of carbon. At stationary phase while virtually no diminution in cellular yield was observed in the presence of 1.0 mM aluminum, only 31% of bacterial yield was recorded in media with 50 mM aluminum. The decrease in soluble aluminum in the culture fluid was concomitant with the formation of a gelatinous residue. At later stages of growth, the trivalent metal was immobilized in this deposit. This bioprecipitate consisted of lipid moieties but was apparently devoid of proteins and carbohydrates. X-ray fluorescence spectroscopy and colorimetric assays also revealed the presence of aluminum and phosphorus. X-ray diffraction spectroscopy indicated that the biomineral was amorphous. Examination of the gelatinous residue by scanning electron microscopy and energy dispersive X-ray microanalysis aided in the identification of aluminum, oxygen and phosphorus rich irregular bodies that were associated with carbon containing thread-like structures.