Mechanism of resistance to cobalt in some Pseudomonas strains

We performed a biophysical and a biochemical analysis of Co2+ effect on the cell outer membrane of Co2+ sensitive Pseudomonas putida BS 394 strain, Co 2+ resistant Pseudomonas spp. BS 501 wild-type strain and Co2+ resistant tr ansformant Pseudomonas putida BS 394 (pBS 501), containing a plasmid BS 501 from wild type strain. The strain resistance to cobalt toxic effect, detec ted on cytoplasmic membrane by cell analytical microelectrophoresis and hig h electroorientation spectroscopic studies, was in following order: Pseudom onas spp. BS 501 > Pseudomonas putida BS 394 (pBS 501) > Pseudomonas putida BS 394. The investigation of cell surface proteins showed for both resista nt strains the synthesis of proteins with molecular weight of 43,7 and 31,6 kD, but not for the sensitive one. The removal of these proteins by a tryp sin treatment lead to the disappearance of Co2+ toxic effect on the membran e permeability, as demonstrated by the electrophysical studies. As a conseq uence, the surface proteins encoded by the plasmid DNA pBS 501 may modify t he electrosurface properties of the resistant cells and therefore protect t hem from the toxic effects of cobalt ions.