Physiological and proteomic responses of Chlamydomonas reinhardtii to arsenate and lead mixtures

Arsenic (As) and lead (Pb) are frequently emitted from various sources into environment, but microbial responses to their combined toxicity have not been systematically investigated. In this study, Chlamydomonas reinhardtii was exposed to two levels of arsenate (As (V), 50, 500 mu g/L), Pb (II) (500, 5000 mu g/L) and their mixture (50 mu g/L As (V) + 500 mu g/L Pb (II); 500 mu g/L As (V) + 5000 mu g/L Pb (II)). The growth of C. reinhardtii was inhibited more remarkably by As (V) than by Pb (II). The As stress was alleviated by Pb in the 50 mu g/L As (V) + 500 mu g/L Pb (II) treatment, but was enhanced upon the 500 mu g/L As (V) + 5000 mu g/L Pb (II) exposure, with more pronounced changes in a number of physiological parameters of the algal cells. Proteomic results showed that 71 differently expressed proteins (DEPs) in the treatment of 50 mu g/L As (V) + 500 mu g/L Pb (II), and 167 DEPs were identified in that of 500 mu g/L As (V) + 5000 mu g/L Pb (II). These proteins were involved in energy metabolism, photosynthetic carbon fixation, reactive oxygen scavenging and defense, and amino acid synthesis. Taken together, these physiological and proteomic data demonstrated that C. reinhardtii could resist the As (V) and Pb (II) combined treatments through extracellular complexation and intracellular pathways.

Automated summary

In combined treatments of As(V) and Pb(II) in Chlamydomonas reinhardtii, lead could alleviate arsenic stress at lower concentrations, but enhance it at higher concentrations. Proteomic results showed 71 differently expressed proteins (DEPs) in the low concentration treatment and 167 DEPs in the high concentration treatment, involving energy metabolism, photosynthetic carbon fixation, reactive oxygen scavenging, defense, and amino acid synthesis.