ADSORPTION OF NICKEL ON ENTEROCOCCUS-HIRAE CELL-WALLS

The metal affinity of Enterococcus hirae cell walls and the relation t o the chemical composition of the wall constituents were investigated, by studying the nickel absorption on purified cell walls of Enterococ cus hirae mutants. The strains of Enterococcus hirae are characterised by their penicillin resistance, the mother strains ATCC9790, the peni cillin-sensitive mutant AS21 and the penicillin-resistant mutant R40 p resent an MIC (minimum inhibitory concentration of penicillin) of 1-2, 0.075 and 80 mu g cm(-3), respectively. Preliminary results showed th at the penicillin-resistant cell wall (R40) had more affinity for nick el than the others. The maximum amount of fixed nickel average 2.03 mu mol of Ni mg(-1) of R40 cells walls, 1.06 mu mol of Ni mg(-1) of AS21 cell walls and 0.96 mu mol of Ni mg(-1) of ATCC cell walls. The Scatc hard model showed at least two types of nickel fixation sites, with lo w and high affinity respectively, and a negative cooperativity between sites. Application of the BET isotherm implies a multilayer adsorptio n process in which one layer does not need to be completely saturated before the succeeding ones. The potentiometric titration curve showed the proton affinity distribution of the cell walls. Two protonation co nstants were obtained, one at pH 4.5 which corresponded to the pK(a) o f a weak acid, and one at pH 7.2 which corresponded to the pK(a) of th e couple of H2PO4-/HPO42-.