Microbial Sensing and Removal of Heavy Metals: Bioelectrochemical Detection and Removal of Chromium(VI) and Cadmium(II)

Abstract

The presence of inorganic pollutants such as Cadmium(II) and Chromium(VI) could destroy our environment and ecosystem. To overcome this problem, much attention was directed to microbial technology, whereas some microorganisms could resist the toxic effects and decrease pollutants concentration while the microbial viability is sustained. Therefore, we built up a complementary strategy to study the biofilm formation of isolated strains under the stress of heavy metals. As target resistive organisms, Rhizobium-MAP7 and Rhodotorula ALT72 were identified. However, Pontoea agglumerans strains were exploited as the susceptible organism to the heavy metal exposure. Among the methods of sensing and analysis, bioelectrochemical measurements showed the most effective tools to study the susceptibility and resistivity to the heavy metals. The tested Rhizobium strain showed higher ability of removal of heavy metals and more resistive to metals ions since its cell viability was not strongly inhibited by the toxic metal ions over various concentrations. On the other hand, electrochemically active biofilm exhibited higher bioelectrochemical signals in presence of heavy metals ions. So by using the two strains, especially Rhizobium-MAP7, the detection and removal of heavy metals Cr(VI) and Cd(II) is highly supported and recommended.

Keywords: Cr(VI); biofilm formation; biosensing of heavy metal contaminants; hexavalent chromium; microbial electrochemistry.

Figure 1

(A) Typical growth curves of untreated cells of Rhodotorula ALT72 and Rhizobium-MAP7, (B) effect of metal ions concentrations on the growth inhibition of Rhodotorula ALT72, (C) sensitivity of Rhizobium-MAP7 to Cr(VI) and Cd(II) different concentrations and (D) responses of Rhodotorula ALT72 and Rhizobium-MAP7 to a single concentration of Cr(VI) and Cd(II). The results recorded after 48 h for the Rhizobium-MAP7 and 60 h for the Rhodotorula ALT72.

Figure 2

Testing the cell viability of treated Rhodotorula ALT72 (A) and Rhizobium-MAP7 (B) using WST-test and (C): testing the cell viability of Pantoea agglomerans using WST-test.

Figure 3

(A) Bio-electrochemical responses of biofilm formed Rhodotorula ALT72 treated with different concentrations of Cd(II). The untreated cells were considered as the positive control and (B) bio-electrochemical responses of biofilm formed Rhodotorula treated with different concentrations of Cr(VI). The untreated cells were considered as the positive control.

Figure 4

(A) Bio-electrochemical responses of biofilm formed Rhizobium-MAP7 treated with different concentrations of Cr(VI). The untreated cells were considered as the positive control and (B) bio-electrochemical responses of biofilm formed Rhizobium-MAP7 treated with different concentrations of Cd(II). The untreated cells were considered as the positive control.

Figure 5

(A) Bio-electrochemical responses of biofilm formed P. agglumerans treated with different concentrations of Cd(II). The untreated cells were considered as the positive control and (B) bio-electrochemical responses of biofilm formed P. agglumerans treated with Cr(VI). The untreated cells were considered as the positive control.