Interactions Between EPS From A Heavy-Metal Resistance Bacterium Citrobacter Freundii JPG1 And Cu²⁺ Transport In Underground Recharging With Reclaimed Water

Reclaimed water recharging to groundwater is an effective way to solve the shortage of water resources in our country.However,there are still traces heavy metals existed in reclaimed water,and its transport through soil and infiltration may cause the groundwater pollution,which is a sensitive issue of concern.Transport and deposition of heavy metals are affected by the nature of the heavy metals and concentration,hydrological conditions of filter layer,biological,and other factors.Impact are more complex when biofilm presence.Research on the copper migration and biofilm EPS formation in the process of the reclaimed water recharging underground could help to reveal the law of the copper migration and deposition in the process of underground recharging,predict heavy metal pollution in groundwater.It could provide scientific theory basis for heavy metals management in groundwater,has a certain theoretical guiding significance.In this article,a heavy metal resistence bacterium Citrobacter freundii JPG1?Genbank accession KU513787?was used to determine the resistance characteristics to a variety of heavy metals.Citrobacter freundii JPG1 MIC to Cu²⁺?Cd²⁺?Ni²⁺?Co²⁺?Ag⁺?Cr₂O₇^2-ion were 3,4,3,2,0.06,2 mM respectively.Common heavy metal ion in groundwater-Cu²⁺ was mainly studied.Strain JPG1 has a good resistance to Cu²⁺,when Cu²⁺ ion concentration was lower than 0.25 m M,there was no inhibition almost.When Cu²⁺ ion concentration was 1 mM,inhibition rate to strain JPG1 was at about 50%.In static experiments,EPS formation ability of strain JPG1 itself and 0.1 mM copper effects on strain JPG1-sand complex EPS were studied respectively.The results showed that strain JPG1 EPS forming ability are relatively strong,strain JPG1 EPS production was 118.82 mg/g·VSS?mg/g·dry weight?,contents of protein and polysaccharide were 90.67 and 28.14 mg/g·VSS.0.1 mM of Cu²⁺ ions influenced the strain JPG1-sand complex EPS contents,make the protein content increased from 491.67 ?g/g to 700 ?g/g,but the content of polysaccharide was maintained at 127-130 ?g/g.Strains JPG1 may produced more extracellular protein to resist the toxic effects of Cu²⁺ ions.Dynamic column experiment was used to study the interactions between Cu²⁺ ion migration and entrapment with complex EPS formation.The results showed that the formation of biofilm leads to complex pore jams,the permeability coefficient is less than 10% of the initial.For 0.1 mM Cu²⁺ ions,strain JPG1-sand complex EPS formation can trap almost ions in column effectively,Cu²⁺ ion concentration in outlet water reached only 3.05% of inlet water.When Cu²⁺ ion transport in column from the bottom up to top,it inhibited the underlying biofilm EPS content firstly,made its EPS production decreased by 36.86%.Cu²⁺ ion could penetrate into sand inside,and promote the EPS secretion in second to fifth layers,EPS increased by 63%-131%.In short,strain JPG1-sand complex EPS in column could hold Cu²⁺ ions effectively.At the same time,Cu²⁺ ion could stimulate the secretion of complex EPS in different extent,they can affect each other,Cu²⁺ ion and strain JPG1-sand complex EPS promote each other.