Effect Of Cd²⁺,Cu²⁺and Zn²⁺ On Physiological Changes And Lipid Accumulation Of Marine Microalgae

Heavy metals(HMs)as naturally occurring elements can influence the growth and physiology of microalgae.The aim of this study is to investigate the effects of single and coupled HMs on the physiology,photosynthetic process,oxidative stress and lipid content of marine diatom,Navicula sp..The results on toxicological research of microalgae and the outlook on using HMs may improve the lipid production of microalgae.This study examined the changes of cell density,growth rate,photosynthetic efficiency(Fv/Fm),in vivo fluorescence,reactive oxidative species(ROS)and lipid accumulation of Navicula sp.under single metal Cd2+(0.1-10 mg/L),Cu2+(1-50 mg/L)and Zn2+(0.5-30 mg/L)at 7 different concentrations and couple HMs Cd2+ with Cue+,Zn2+ with Cu2+,and Cd2+ with Zn2+ at 9 concentrations,respectively.This study found that:1)HMs at low concentrations can enhance the growth,but HMs at high concentrations inhibited the growth and photosynthesis,causing the decline in microalgal cell density.Cu2+ coupled with Cd2+ or Zn2+induced synergistic effect on toxicity;2)low concentrations of Cu2+(0-2 mg/L)or Zn2+(0-5 mg/L)improved the in vivo fluorescence,but single metal at all concentrations inhibited the Fv/Fm.The correlation between Fv/Fm and in vivo fluorescence indicated that the decline in Fv/Fm might result from the decrease of in vivo fluorescence;3)single Cu2+(>5 mg/L)stimulated ROS,but single Cd2+ or Zn2+ could not induce ROS formation,while the couple HMs,Cd2+ with Zn2+ at higher concentrations,apparently induced the increase in ROS content.With the existence of Cu2+,the higher Zn2+ concentration is,the lower the ROS production will be;(4)high HMs concentrations,could induce lipid content accumulation.10 mg/L Cd2+,15 mg/L Cu2+ and 30 mg/L Zn2+ improved lipid accumulation.Once the concentration of HMs surpassed the tolerant ranges,all metabolisms including lipid production are inhibited.Zn2+ coupled with Cu2+exhibited the best effects on lipid stimulation,Cd2+ coupled with Cu2+(2 mg/L),which drastically inhibited the growth and photosynthesis,could induce the accumulation of lipid.