Characteristics And Adsorption Properties Of Pseudomonas Aeruginosa And Alcaligenes Faecalis EPS Under Different Exogenous Cd(?) Stress/induction

Extracellular polymeric substances(EPS)has become an efficient and environmentally friendly new adsorbent due to its rich functional groups and excellent adsorption properties for heavy metals.By means of heavy metal stress/induction,the strain can be stimulated to produce more EPS.However,previous studies have attributed the stress/induction effect to heavy metal cations,while ignoring the effect of anions.And most studies have focused on gram-positive bacteria and rarely focused on gram-negative bacteria.In this thesis,three Cd(?)compounds were used to stress culture Pseudomonas aeruginosa and Alcaligenes faecalis,to explore the effects of different anions on the yield,composition and adsorption of EPS in the process of heavy metal stress/induction of gram-negative bacteria.It was found that NO₃^-could promote the strain to produce EPS containing more protein.The adsorption properties of EPS for Cd(?)were also investigated.The adsorption properties of EPS for Cd(?)were also investigated.EPS under different stress conditions were analyzed by 3D-EEM,HPLC,FTIR and XPS,and found that the content of C=O,-NH₂,-COOH and other functional groups increased after stress/induction.Finally,EPS before and after Cd(NO₃)₂ stress/induction was used as adsorbent to explore the adsorption law of EPS on Cd(?)and Zn(?)under different conditions in the presence of single and bimetallic ions,and found that EPS has a higher affinity for Cd(?).The main conclusions are as follows:(1)When different concentrations of Cd Cl₂,Cd SO₄ and Cd(NO₃)₂ were used to stress/induce Pseudomonas aeruginosa and Alcaligenes faecalis,Cd(NO₃)₂ had the best stress effect,indicating that NO₃^-was used as an N source by the strain to synthesize protein,improve the yield of EPS,and then improve the adsorption capacity of EPS.For Pseudomonas aeruginosa,when the concentration of Cd(NO₃)₂ was 50 mg/L,EPS reached 214.96 mg/g VSS,in which the protein content was four times higher than that before stress induction.Under this condition,the adsorption capacity of EPS was the highest.For Alcaligenes faecalis,when the concentration of Cd(NO₃)₂ was 20 mg/L,EPS reached 109.17 mg/g VSS,in which the protein increased by half compared with that before stress/induction.Under this condition,the adsorption capacity of EPS was also the highest.(2)The results of HPLC showed that after stress/induction,the proportion of serine,glutamate,proline,lysine and phenylalanine in EPS increased,which improved the adsorption capacity of EPS.The results of FTIR showed that the concentration of functional groups in EPS increased after stress/induction of three Cd(?)compounds,and the content of functional groups in EPS obtained after Cd(NO₃)₂ stress was the highest,such as C-O,C-N,N-H and so on.XPS was used to analyze the C and O elements in EPS.After stress/induction,part of the C chain breaks and combined with O and N elements to form C-(N,O).Among them,the proportion of C-N/C-O and C=O in EPS obtained after Cd(NO₃)₂ stress was the highest.(3)The adsorption experiments of Pseudomonas aeruginosa EPS and Alcaligenes faecalis EPS on Cd(?)and Zn(?)showed that the adsorption capacity of EPS before and after stress/induction increased with the increase of p H,while the effect of temperature on the adsorption capacity of EPS was relatively small.The adsorption data of Cd(?)and Zn(?)by EPS accord with Langmuir model,The theoretical maximum adsorption capacity of Cd(NO₃)₂-EPS_P.Aand Cd(NO₃)₂-EPS_A.F was higher than that before stress.The kinetic results show that the adsorption process of Cd(?)and Zn(?)by EPS is more in line with the pseudo second-order kinetic model.(4)The fitting results of competitive Langmuir model show that when Cd(?)and Zn(?)exist at the same time,they will compete for the adsorption sites on EPS.The inhibitory effect of Cd(?)on Zn(?)is higher than that of Zn(?)on Cd(?),and EPS has higher affinity for Cd(?).