Fluorescent Probe Based Sensing, Chromium And Cadmium Distribution In Electrochemically Active Bacteria

Bioelectrochemical systems are emerging as a new technology for waste treatment andresource recovery that function on the basis of electrochemically active bacteria(EAB),often used to represent both microbial fuel cells(MFCs)and microbial electrolysis cells(MECs),reflecting the critical roles of EAB in metal and resource recovery in BESs.However,the mechanism of metal removal and recovery by EAB has always been a research hotspot and difficulty in this field.Small molecular metal fluorescent probe was EAB cell permeable and an effective intracellular metal ions sensing without damaging cells,which is an efficient method in cell imaging and quantification of metal ions.Since these fluorescent probes are expected to image and quantify metal ions in the EAB has not been previously reported.In this study,we chose Cr(III)or Cd(II)fluorescent probe and evaluated its application for the direct sensing of metal ions and the subsequent mapping of the distribution of various valence states of metal in the EAB,which is expected to clarify the mechanism of metal removal from biocathode BESs.Main results include:(1)Four electrochemically active bacteria were isolated from mixed-culture Cr(VI)-reduced biocathode MFCs,identified and tentatively termed as Stenotrophomonas sp.YS1,Stenotrophomonas maltophilia YS2,Serratia marcescens YS3,Achromobacter xylosoxidans YS8.Strain YS3 exhibited the highest activities,which had the highest OCVs(0.384 V),maximum power(18 μW),average circuit current(0.19 ± 0.01 m A),cathode potential(-0.13 ± 0.0 V),Cr(VI)reduction(84.0 ± 1.6%),and the highest ability for intracellular chromium accumulation.This result of sensing Cr(III)ions by fluorescent probe illustrates that cathode directed more Cr(VI)for entering these EAB cell membranes for subsequent reduction in the EAB.(2)Four electrochemically active bacteria were isolated from mixed-culture Cd(II)-removal biocathode MECs,identified and tentatively termed as Ochrobactrum sp.X1,Pseudomonas sp.X3,Pseudomonas delhiensis X5,Ochrobactrum anthropi X7.The addition of 2,4-dinitrophenol(2,4-DNP)with an appropriate concentration of 0.25 m M nearly changed Cd(II)removal and hydrogen production under applied voltage of 0.5 V.Current directed the distribution of Cd(II)ions in the electrotrophs with the occurrence of an initial quicker import and the subsequent quicker export,both of which were somewhat inhibited by 2,4-DNP.Interms of total cadmium,current always directed less cadmium in catholyte and electrotrophs with independence of the presence of 2,4-DNP.Cd(II)fluorescent probe was used to imaginably and quantitatively map Cd(II)ions in EAB and its response to current and2,4-DNP of the distribution of different forms of cadmium,and thus benefits for clarifying the roles of current and 2,4-DNP in electrotrophic removal of Cd(II)ions,by which the import and export Cd(II)ions systems in the electrotrophs had been changed.