Tolerance and uptake of heavy metals by Pseudomonads

A group of Pseudomonads, previously isolated from wastewater, was used to study the accumulation of a specific metal in the presence of a second binary metal or a combination of other metal(s). The growth of Cr(VI)-resistant Pseudomonas fluorescens strain was directly inhibited when the Cr(VI) concentration reached 3 mmol/L. The presence of binary metal ions decreased the amount of accumulated Cr(VI). Furthermore, a Pseudomonas putida strain was shown to tolerate Cu(II) up to a concentration of 3 mmol/L, while higher concentrations (>4 mmol/L) showed a greater inhibitory effect. This pattern of inhibition was varied in the presence of other binary metal ions. Another P. putida strain (Ni(II)-resistant) tolerated Ni(II) concentration up to 5 mmol/L. For this isolate, the use of Cu(II) as binary metals was not effective, while, Cd(II) and Cr(VI) had a significant influence on the bacterial growth. The growth of Cd-resistant (P. putida) strain in the presence of Cd concentration up to 10 mmol/L was variable. This fluctuation was also observed in the presence of other metal ions. For this strain, Cu and Ni showed relatively similar behaviour. The best Cr(VI) accumulation (13.26 mg/L) was obtained by the Ni(II)-resistant strain, while that of Cu(II) accumulation (151.42 mg/L) and Ni(II) accumulation (54 mg/L) took place by Cd(II)-resistant strain. Among all metal ions tested, the highest Cd accumulation was 182.37 and 160.17 mg/L. These were obtained by the Ni-resistant strain and the Cd-resistant strain, respectively.