Effects of yttrium under lead stress on growth and physiological characteristics of Microcystis aeruginosa

Yttrium is a main kind of rare earth elements (REEs) with wide applications in modern industry and farming. Lead has been considered to be one of the most important heavy metal pollutants due to its environmental persistence and tendency. In order to clarify the effects of REEs on cyanobacteria in case of suffering heavy metal pollutants, we investigated the effect of different concentrations of yttrium ion (Y3+) on the common blue-green microalgae Microcystis aeruginosa, grown under conditions of lead ion (Pb2+) stress. Growth and physiological status were tested involving several important enzyme of antioxidant defense system (superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), malondiadehyde (MDA), chlorophyll a (Chl-a), soluble sugar and Microcystin-LR (MC-LR) in cultured experiments. Results indicated that growth of M. aeruginosa was stimulated when treated less than 0.50 mg/L Y3+ and 0.20 mg/L is the optimum concentration. With the increasing content of Chl-a and activity of SOD, POD, CAT at the 12th day at relatively low concentration of Y3+ treatment (<= 0.20 mg/L), enhancement of photosynthesis and the improvement of eliminating active oxygen on M. aeruginosa were observed. On the contrast, soluble sugar content on algae reduced as the treatment of initial Y3+ concentration was in the range of 0.00-0.50 mg/L. Besides, there was a significant accumulation in both contents of MDA and MC-LR exposed from 1.00 to 5.00 mg/L Y3+, indicating that the ruin of antioxidant defense system and further aggravation to the existence of algal cell may be due to MC-LR releasing. M. aeruginosa might suffer a more positive physiological impact for exposure of relatively low Y3+ concentration against Pb2+ stress harm, which provided a far-reaching significance on blue-green algae research.