Interference of heavy metals on the photosynthetic response from a Cr(VI)-resistant Dictyosphaerium chlorelloides strain

Abstract

The successful selection of a particular type of bioelement and its association to the appropriate transducer determines the specificity of a biosensor. Therefore, from a strain of chloroficea Dictyosphaerium chlorelloides, modified in laboratory to tolerate high Cr(VI) concentrations, the possible interferences of other heavy metals on photosynthetic activity were studied. After exposing wild type and Cr(VI)-resistant cells to increasing Ag⁺¹, Co⁺², Hg⁺², Cr⁺³, Cu⁺², Zn⁺², Fe⁺³ and Cd⁺² concentrations, both photosynthetic quantum yields was compared. Photosynthetic electron transport rates were measured with a TOXY-PAM chlorophyll fluorometer, non-linear regression analysis of each of the toxicity tests was done, and means of both groups were compared using unpaired t test. The results show no significant differences between both cell types when they were exposed to Ag⁺¹, Co⁺², Hg⁺², Cr⁺³, Cu⁺², Fe⁺³ and Cd⁺² metal ions, and extremely significant differences (p < 0.0001) to Zn⁺² exposures. These results demonstrate the suitability of this Cr(VI)-resistant type D. chlorelloides strain as a suitable bioelement to be coupled to a biosensor based on dual-head microalgae strategy to detect and quantify Cr(VI) in water courses and waste water treatment plants. However, some disturbance may be expected, especially when certain analyte species such as zinc are present in water samples tested. The analysis of binary mixtures between Zn⁺² and other heavy metals showed a slight antagonistic phenomenon in all cases, which should not alter the potential Zn⁺² interference in the Cr⁺⁶ detection process.