EFFECTS OF HEAVY-METALS ON PSEUDOMONAS-AERUGINOSA AND BACILLUS-THURINGIENSIS

The biosorption of the heavy metals most frequently, found in polluted environments by Pseudomonas aeruginosa and Bacillus thuringiensis was studied The effects of these metals on bacterial growth, quantity of dry cells, ammonium assimilation pigment production, and protein synth esis were investigated. At lower concentrations than the minimal inhib itory concentration (MIC), the metals partially limited bacterial grow th and caused an inhibition proportional to the metal concentration ap plied. The production of bacterial biomass varied according to the nat ure and concentration of the metals, and to the bacterial strain studi ed The biosorption of metals by P. aeruginosa and B. thuringiensis was variable. Mercury and copper appeared to be the elements most adsorbe d by bacteria. Citrate noticeably increased the biosorption of chromiu m by P. aeruginosa (0.07-45.9%) and copper by B. thuringiensis (18.7-3 3.8%). Metallic cations everted variable effects on protein synthesis. Zinc stimulated protein synthesis in P. aeruginosa, and cadmium inhib ited it significantly in B. thuringiensis. Mercury and cobalt, at conc entrations below the MIG, always inhibited the synthesis of pigments i n P. aeruginosa. The strong interactions of mercury and copper with or ganic matter suggest that these undesirable elements might be removed from the environment by bacterial trapping and sequestration. A better understanding of the different for-ms of metals actually existing in polluted environments (speciation) would be of gr eat interest. (C) 19 98 Elsevier Science Ltd. All rights reserved.