MICROBIAL ADAPTATION TO ALUMINUM

The presence of aluminum in a minimal mineral medium, with citrate as the sole source of carbon, elicited the production of an exocellular l ipid-rich residue in Pseudomonas fluorescens. Although aluminum affect ed the growth rate, no apparent diminution in cellular yield was obser ved in medium supplemented with up to 3 mM of the trivalent metal. Whi le a 10% reduction in cellular yield was recorded in medium with 7.5 m M aluminum, a decrease of 69% was reported in medium supplemented with 50 mM aluminum at stationary phase of growth. The wet weight of the p ellet ranged from 5.9 to 70.3 mg mL(-1) of culture in medium supplemen ted with 1-30 mM aluminum. The trivalent metal was immobilized in this precipitate and associated with phosphate moieties. Both neutral lipi ds and phospholipids constituted the pellet. More than 90% of the weig ht of the wet pellet was lost following lyophilization. The percentage of aluminum immobilized increased with the concentration of trivalent metal in the medium. Preconditioned cells showed an improved growth r ate, and the cellular yield was slightly higher than for unadapted cel ls.