Study On The Characteristics And Adsorption Properties Of Pseudomonas Aeruginosa And Alcaligenes Faecalis EPS Under Cd(?) Stress

Bacterial extracellular polymer(EPS)is a new type of biosorbent that is widely concerned by researchers at home and abroad because of its great adsorption potential for heavy metal ions in water.The production of EPS is a self-protection mechanism for microorganisms to slow down or eliminate adverse effects,and the protein components play a very important role.Among the common heavy metals in nature,cadmium is highly toxic to the growth of bacteria,and it has strong stress to bacteria to produce EPS.In this study,two typical gram-negative bacteria that are Pseudomonas aeruginosa and Alcaligenes faecalis were selected to explore the changes of the EPS components,especially the protein components,on the surface of different bacteria under different concentrations of Cd(?)stress,and analyze the correlation between protein component,polysaccharide component,protein/polysaccharide and adsorption capacity.Then using scanning electron microscope(SEM),Fourier infrared spectroscopy(FTIR),three-dimensional fluorescence spectroscopy(3D-EEM)and X-ray photoelectron spectroscopy(XPS)to analysis of the bacterial surface morphology,functional groups,components and element morphology changes in the EPS.It was deeply discussed of the relationship between the EPS characteristics of the bacterial surface and the adsorption performance of heavy metals.Finally,Pseudomonas aeruginosa EPS was selected to explore the effect of different adsorption conditions on the adsorption performance of EPS because of obvious stress effect.The main conclusions are as follows:(1)Under different Cd(?)stress conditions,the total amount of Alcaligenes faecalis and Pseudomonas aeruginosa EPS reached the maximum values of 111.71mg/g VSS and 214.96 mg/g VSS at Cd(?)stress concentrations of 20 mg/L and 50mg/L,respectively,in which the protein component content change law is similar to it and the most significant,the optimal point of stress increased by 60.38%and 409.69%respectively compared with without stress.The regulation effect of Cd(?)on the EPS of the two strains,Pseudomonas aeruginosa is better than that of Alcaligenes faecalis.(2)Before and after stress,Alcaligenes faecalis and Pseudomonas aeruginosa EPS at Cd(?)stress concentrations of 20 mg/L and 50 mg/L achieved the best results,respectively.And the adsorption capacity are 208.33 mg/g and 232.45 mg/g respectively,Pseudomonas aeruginosa EPS has better adsorption effect.The correlation between protein content and adsorption capacity was the highest,and the correlation between Pseudomonas aeruginosa EPS protein content and adsorption capacity was achieved 0.7914.(3)The surface morphology of the bacteria through SEM observation showed that the surface flocs of the two strains after stress were more than those without stress.Among them,the contrast of Pseudomonas aeruginosa before and after stress was more obvious,and the surface flocs of Pseudomonas aeruginosa after stress were more obvious than that of Alcaligenes faecalis.In addition,the cell integrity of the two strains after EPS extraction is nice,indicating the feasibility of EPS heating extraction method.(4)FTIR results show that EPS contains-OH,CN,NH,-COOH and C=O and other functional groups which have strong affinity with heavy metal ions,and the content and types of functional groups of Pseudomonas aeruginosa EPS are the most abundant after stress;3D-EEM results show that fluorescence intensity of Pseudomonas aeruginosa EPS changed significantly before and after stress,and the protein content of EPS was the highest;XPS results showed that the element morphology of EPS was changed before and after stress of the two strains.The functional groups in EPS of Pseudomonas aeruginosa stress were more increased such as C=O?C-OH and R-NH₂groups.(5)Pseudomonas aeruginosa EPS,which has a more obvious stress effect,was selected to explore the effect of different adsorption conditions on the adsorption performance of EPS.The results showed that the reaction temperature has a small effect on the adsorption effect of the adsorbent,while the p H value of the reaction has a greater effect.Before and after stress,EPS can reach adsorption equilibrium when the reaction time reaches 20 min and conforms to the quasi-second-order kinetic law.The Langmuir model calculates that the theoretical maximum adsorption capacity of Control-EPS and Cd-EPS for Cd(?)reached 1010.65 mg/g and 1663.34 mg/g,indicating that the strain EPS is a kind of biosorbent with good adsorption performance and the EPS under stress has better adsorption potential.