Study On Lead And Cadmium Tolerance Of Curvularia Tsudae C12

In this study,a strain of Curvulariasp.C12 was isolated from the roots of Phragmites australias,which can tolerate high lead and cadmium stress.we identified it based on morphological characteristics and molecular identification.Then its tolerance to different mass concentrations of Cd²⁺?0³20mg/L?and Pb²⁺?0¹200 mg/L?were studied both in solid and liquid culture conditions by measuring its changes of growth mass andcomparing pH value and organic acids contents,as well as glutathione?GSH?and malondialdehyde?MDA?contents in the fungal mycelia.The tolerance ability of Curvulariatsudae C12 to Cd²⁺and Pb²⁺were assessed and then the related tolerance mechanism was preliminarilyanalyzed and discussed.The results couldprovide thefoundationforrevealing the mechanism of fungal resistance to heavy metal,and for the application of fungi to controlheavy metal pollution.The main results are as follows:1.We identifieda strain of Curvulariasp.C12 which can tolerate high lead and cadmium stressas Curvulariatsudae.2.Curvularia tsudae C12 showed high cadmium tolerance,when the mass concentrations of Cd²⁺was up to 320 mg/L,it still grew.And its growth and cadmium tolerance were obviously better under liquid culture condition.Under solid culture condition,it didn't form hyphal coils and along with the increase of Cd²⁺mass concentrations,the mycelia dry weight of C.tsudae C12 was increased firstly and then decreased,and reached the maximum at 20 mg/L?P<0.05?;Under liquid culture condition,the colour of mycelium ball was creamy-white,and it had smooth surface and no spikes.The myceliadry weightwas gradually reduced in liquid culture condition?P<0.05?.3.Under the environmental stress of Cd²⁺,the liquid culture medium content four kinds of organic acids: citric acid,malic acid,succinic acid and acetic acid.Oxalic acid and tartaric acid did not be detected,while citric acid and malic acid content were relatively high,and succinic acid was only produced under high concentrations of Cd²⁺?80³20mg/L?.With the increase of Cd²⁺mass concentrations,four kinds of organic acidsas well as GSH content in mycelia were increased firstly and then decreased,and reached the maximum at 160mg/L?P<0.05?;while MDA content in mycelia was increased firstly,then decreased and later rose again,but did not show significantdifference?P>0.05?.pH values were significant lower than that of control?without cadmium??P<0.05?,however,did not change significantly?P>0.05?along with the increase of Cd²⁺mass concentrations.The accumulation of GSH and organic acids?especially citric acid,malic acid and succinic acid?maybe one of the underlying mechanisms for C.tsudae C12 to reduce the damage of cadmium and to improve its cadmium tolerance.4.C.tsudae C12 showed high lead tolerance,and it could grow under 1200 mg/L ofPb²⁺.Under solid culture condition,it formed hyphal coils with Pb²⁺stress and along with the increase of Pb²⁺ mass concentrations,the myceliadry weight of C.tsudae C12 was increased firstly and then decreased,and reached the maximum at 400 mg/L?P<0.05?;Under liquid culture condition,the colour of mycelium ball was black,and it had spikes on the surface.The myceliadry weightdid not change significantly?P > 0.05?under Pb²⁺concentrations of 0⁸00 mg/L.Compared with the control and the Pb²⁺concentrations of 400 mg/L,the myceliadry weight under Pb²⁺ concentrations of 1200 mg/L were decreased by 24%?P>0.05?and 37%?P<0.05?,respectively.5.Under the environmental stress of Pb²⁺,we detect oxalic acid in the liquid culture medium content.The content of oxalic acid increased significantly with the increase of Pb²⁺mass concentrations?P<0.05?and reached the maximum at 1200mg/L?21.2 mg/mL?.However,pH values did not change significantly?P>0.05?,treatment groups were significant lower than that of control group?without lead??P<0.05?,along with the increase of Pb²⁺mass concentrations.GSH content in mycelia were increased firstly and then decreased.In addition,under different Pb²⁺concentratons,the study determined theintracellular and extracellular Pb²⁺concentration of C.tsudae C12 and characterized fungal hyphae by SEM.The results showed that the cell of C.tsudae C12 could strongly enrich Pb²⁺ and adsorption efficiency increased with increasing Pb²⁺concentrations.6.Under different heavy metals(Cd²⁺and Pb²⁺)stresses,C.tsudae C12 had different responses mechanism in mycelial morphology and physiological and biochemical changes,which showedthe strong adaptability of microorganism.