The Cd Biosorption Mechanism Of Strptomyces Cavourensis TJ430 And Pseudomonas Fluorescens P32 And Its Effects On Cd Accumulation In Rice

Heavy metal pollution is one of the major food safety threatening factors and Cadmium?Cd?pollution has become an upcoming problem recently in rice production.There are three methods to control Cd pollution in rice field and these are physical,chemical and biological control measures.However,biological control method has become popular due to its advantages over the other two include low cost,high pollution and clean way of reducing heavy metal pollution in rice production..A study on Cd resistant microbe and its effect on rice rhizosphere environment as a measure to reduce high Cd accumulation in rice fields was done.A known high Cd accumulation variety T705 was used to test biosorption effects of two microbes Strptomyces Cavourensis TJ430 and Pseudomonas fluorescens P32 in different stress levels of Cd.The results revealed that::1.Both Cavourensis Streptomyces TJ430 and Pseudomonas fluorescens P32 have strong resistance to Cd,the minimum inhibitory concentration of Cd on TJ430 and P32 are 80 mg·L^-1 and 150 mg·L^-1respectively.This was seen clearly by use of growth curve,the strain of TJ430 and P32 under Cd stress comparing with strains in the natural growth condition.With the increase of Cd concentration,the strains showed different degree of toxicity.5 mg·L^-1Cd concentration resulted in biosorption rate of94.6%and the biosorption capacity was 1.65 mg·g^-1 dry weight.With the increase of Cd concentration,the biosorption rate of both strains decreased,but the decrease of P32 is not obvious.Maximum biosorption capacity was reached for TJ430 and P32 at optimum pH of 5 and 6 respectively,both inoculums of 3%and osmotic pressure of 0.6%.2.The kinetics of cadmium biosorption by Streptomyces Cavourensis TJ430 and Pseudomonas fluorescens P32 showed that in the top 60min for fast biosorption stage,then biosorption gradually slow,and finally tends to balance.TJ430 reached equilibrium stage at about 400min(biosorption capacity15.59 mg·g^-1)and that for P32 was at about 690min(biosorption capacity is 20.03 mg·g^-1).TJ430 and P32 simulation of pseudo first order dynamics simulation correlation coefficient R² was 0.986 and 0.912,and the pseudo second order dynamics simulation correlation coefficient R² value was 0.999 and 0.998respectively which means that the fitting degree of pseudo second order dynamics was high.It is concluded that the biosorption of cadmium by bacteria is not only the surface adsorption,but the biosorption of chemical mechanism.During the biosorption process of Cd for both strains,the groups–OH,C=O,-N-H-,-C-O-,-P-O-C-,-C-H-,-CH₃ had obvious vibration,in which the groups-OH?C=O?-C-O-had the most obvious vibration,means that these functional groups play an important role in the process of cadmium biosorption.3.From the pot experiments,addition of both treatments resulted in significant increase in rice chlorophyll content at tillering stage.There were no significant difference between the two treatments;there were bacteria treatment and interaction effect between bacteria treatment and fertilizer on rice soil which resulted in Cd content reduced.Addition of TJ430 and P32 to the soil,compared with the control group can reduce 0.6 mg·kg^-1Cd content in root.The effect was more obvious after addition of organic fertilizer,as the Cd content was decreased by 1.32 mg·kg^-1 and 1.21 mg·kg^-1 respectively.Also the activities of POD and SOD in roots and leaves of rice at tillering stage were increased after adding treatments.P32 treatment and fertilizer interaction significantly improved the root and significantly increased both leaf POD and SOD hence effective elimination of oxygen activity in rice.TJ430fertilizer interaction can significantly reduce soil available Cd content,as it was decreased by 18.46%,4.Using phospholipid fatty acids in high flux sequencing,discussed the colonization in the rhizosphere of rice strains.The results showed that not add organic fertilizer?novogro?under the condition of the relative abundance of Pseudomonas was 2.83%and Streptomyces less than 1%,not shown in the bar chart;in the treatment which add organic fertilizer Streptomyces abundance was significantly increased,reached to 2.05%,but the relative abundance of Pseudomonas was not increased significantly,the abundance of bacillus and Lactococcus the increase was obvious,indicating that addition of organic fertilizer contributes to the colonization of TJ430,but the effect on P32 is not obvious,and it also changes the flora distribution of rice rhizosphere.