Regulation And Influence In The Process Of Electroactive Biofilms Formation Under Low Concentrations Of Heavy Metals

Electroactive biofilms（EABs）are the core components of bioelectrochemistry（BESs）,which have wide application prospects in fuel production,bioelectrocatalytic synthesis and bioreactor due to their characteristics of extracellular electron transfer.How to promote the formation of EABs and improve the performance of BESs has always been a research hotspot in the field of bioelectrochemistry.Seven heavy metal ions Cu²⁺,Cd²⁺,Co²⁺,Zn²⁺,Mn²⁺,Ni²⁺and Cr³⁺were introduced into BESs in this study to explore their effects on the performance of BESs at low concentrations.Meanwhile,their effects on the formation of EABs were analyzed by means of confocal laser,high-throughput sequencing and metagenomic sequencing.Analysis of the BESs electrochemical performance under different heavy metals conditions,found that all heavy metal ions showed inhibition of BESs electricity generation at 1 mg/L,and only Cu²⁺,Cd²⁺and Co²⁺could promote BESs electricity generation at 10μg/L and 100μg/L,The specific performances are as follows:Adding 10μg/L and 100μg/L Cu²⁺can increase the current density by 58.79%and 38.63%,while the current density decreased 18.08%with the addition of 1mg/L Cu²⁺.The current density increased by16.20%and 17.8%by adding 10μg/L and 100μg/L Cd²⁺,while the current density decreased 47.25%with the addition of 1mg/L Cd²⁺.The current density increased 50.25%and 32.4%by adding Co²⁺of 10μg/L and 100μg/L,while the current density decreased13.88%with the addition of 1mg/L Cd²⁺.Cyclic voltammetry showed that the electroactivity of Cu²⁺,Cd²⁺,Co²⁺at 10μg/L and100μg/L was higher than that of the control group,and the Coulombic efficiency of corresponding BESs was also improved.The coulombic efficiency increased from26.22±0.65%to 40.99±5.39%and 37.94±4.08%after adding 10μg/L and 100μg/L Cu²⁺,respectively.The coulombic efficiency increased from 28.42±5.48%to 28.95±0.7%and30.42±4.32%after adding 10μg/L and 100μg/L Cd²⁺,respectively.The coulombic efficiency increased from 18.77±1.77%to 26.41±4.2%and 20.4±1.55%,respectively,with the addition of Co²⁺of 10μg/L and 100μg/L.The enhanced activity of bofilm was atrributed to the enhancement of biomss on the anode.Confocal analysis of biofilm protein content and laser confocal analysis showed that the biomass and relative activity ratio of biofilm in experimental group were higher than that in control group.The results of population analysis showed that after electrochemical acclimation,the proportion of electrogenerative Geobacter in biofilm communities was increased;Among them,Geobacter is more sensitive to Cu²⁺.Under the condition of mixed culture,Cu²⁺of 10μg/L and 100μg/L can increase the proportion of Geobacter in biofilm community and improve the electrochemical performance of electroactive biofilm.Under the condition of pure culture,while the relative abundance of Geobacter wasn’t improved by adding 10μg/L and 100μg/L Cu²⁺,Cd²⁺.In additon,the regulation of mechanism under different Cu²⁺concentrations was studied.At 96h,the biomass of 10μg/L and 100μg/L Cu²⁺was increased 87.8%and 80.2%respectively.1mg/L of Cu²⁺completely inhibited the proliferation of G.sulfurreducens PCA.During the cultivation,the OD₆₀₀of this sample stabilized at 0.05±0.003.The results of Metagenomic sequencing showed that the expression of"energy production and conversion","signal transduction mechanism","coenzyme transport and metabolism","inorganic ion transport and metabolism"and other related functional genes were affected by Cu²⁺.At the same time,Cu²⁺of 10μg/L and 100μg/L significantly up-regulated the genes of type IV pili,Some c-type cytochrome related genes were down-regulated,but the down-regulation effect was not significant.Cu²⁺at 1 mg/L inhibited type IV pili and c-type cytochrome related genes significantly.In BESs,EABs is the key factor affecting the extracellular electron transfer.This study provides an effective method to regulate the formation of EABs,and also provides a new idea for BESs to treat trace heavy metal wastewater,which promotes the development of BESs technology.