Phytochelatin production in freshwater algae Stigeoclonium in response to heavy metals contained in mining water; effects of some environmental factors

Abstract

Production of phytochelatins (PC) in two freshwater, filamentous green algae of the genus Stigeoclonium, in response to heavy metals contained in mining water was studied. Stigeoclonium sp. grown abundantly in ditches with the mining water (southern Poland) accumulated high amounts of heavy metals. The other studied alga Stigeoclonium tenue Kütz. was isolated from unpolluted lake water in the Netherlands. Both algae exposed to the heavy metal mixture (17 μM; mainly zinc) contained in the hard, alkaline (pH 8.2) mining water produced similar amounts of phytochelatins (PC 2 and PC 3): 500–600 nmol SH g −1 dry weight. After water acidification to pH 6.8, a >2-fold increase of the total phytochelatin level as well as the appearance of longer chain peptide PC 4 in the cells of both algae was observed. The concentration of labile forms of zinc in the acidified mining water was four times as high as that in the alkaline water. The heavy metal mixture (17 μM) in non-complexing solution of pH 6.8 caused a comparable phytochelatin production in both Stigeoclonium strains as the same mixture present in the acidified mining water. However, in the non-complexing solution of pH 8.2, the metal mixture induced in algae more PCs than at pH 6.8. A positive effect of bicarbonate enrichment in the solution on the PC production in S. tenue was also observed. Stigeoclonium sp. exposed to high concentrations (10 μM) of individual metals (Zn, Pb and Cd available as free cations) synthesised much higher amounts of phytochelatins (PC 2–PC 4) than in response to the metal mixture contained in the mining water. The order of PC induction by the studied metals in the Stigeoclonium sp. was Cd>Pb>Zn. Addition of suspended solid matter to the heavy metal solution resulted in essential quantitative changes in phytochelatins in algal cells; a considerable decrease of PC 2, PC 3 and PC 4 levels was observed. The PC production in algae of the genus Stigeoclonium exposed to the heavy metal mixture is discussed in the context of various metal bioavailability and the algal adaptation to complex aquatic environment.