Application Of Metal Fluorescent Probes For Tracking Cr(?), Cu(?) Or Cd(?) Ions In Electrochemically Active Bacteria Isolated From Biocathode Bioelectrochemical Systems

Bioelectrochemical systems (BESs) is one newly developed technology for wastewaters treatment with simultaneous metal recovery. Different from chemical catalyzed abiotic cathodes, biocathode BESs, which utilizes electrochemically active bacteria as catalysts exhibited multiple merits including low cost, sustainability and little sludge generation. Despite great attention on biocathode BESs for metal recovery during the past couple years, metal reduction, particularly metal distribution in association with the electrochemically active bacteria is still unknown. Some certain metal fluorescent probes are minor organic compounds with molecule weights at a range of 500-1000. These probes can specifically recognize metals in active cells, exhibiting merits of high sensitivity, simplified sample preparation, no harm to active cell, and imageable picture. Based on these considerations, metal probes specifically recognizing Cr(?), Cu(?) or Cd(?) were used, respectively to track the Cr(?), Cu(?) or Cd(?) in associated with bacteria. Deeper insight into these aspects will not only deepen our understanding of capability of metal reduction associated with electrochemically active bacteria in BESs, but also broaden the applicable metal fluorescent probes in the field of environmental science.Main results included:(1)Cr(?) probe (R1) was applied to successfully track Cr(?) ions in four Cr(VI)-reduced electrochemically active bacteria of Stenotrophomonas sp. YS1, Stenotrophomonas maltophilia YS2, Serratia marcescens YS3 and Achromobacter xylosoxidans YS8. Fluorescence imaging associated with the four electrochemically active bacteria at various operational periods was achieved using Confocal Laser Scanning Microscopy (CLSM). In a cycle of Cr(?)-reduced MFCs, as the reduction of Cr (?), the concentration of Cr (?) in the electrochemically active bacteria increase gradually.(2) Cu(?) probe (R2) was successfully used to image Cu(?) ions associated with electrochemically active bacteria of Stenotrophomonas maltophilia JY1, Citrobacter sp. JY3, Pseudomonas aeruginosa JY5 and Stenotrophomonas sp. JY6 at various operational periods. Distribution of Cu in intracellular, periplasmic, and membrane-related sections was thus obtained. In a cycle of Cu(?)-reduced MFCs, as the reduction of Cu (?), the concentration of Cu (?) in the intracellular and periplasmic sections first increases and then decreases. After 5 h, total Cu content in biofilm accounts for most of the whole Cu. As a consequence, Cu distributed in association with the cathode electrode, catholyte and electrochemically active bacteria was quantitatively calculated. As the reduction of Cu (?), adsorbed total Cu content on electrode increases gradually, total Cu content in catholyte gradually rdecreases, total Cu content in becteria first increases and then decreases. After 5 h, adsorbed total Cu content accounts for most of the whole.(3) Cd(?) probe (Q3) was successfully used to quantitatively track Cd(?) ions in association with electrochemically active bacteria of Ochrobactrum sp. ST1, Pseudomonas sp. ST3, Pseudomonas delhiensis ST5, and Ochrobactrum anthropi ST7 at various operational periods. Accordingly, distribution of Cd in intracellular, periplasmic, and membrane-related sections was obtained, In a cycle of Cd(?)-reduced MECs, as the reduction of Cd (?), the concentration of Cd (?) in the intracellular and periplasmic sections first increases and then decreases. After 5 h, total Cd content in biofilm accounts for most of the whole Cd. Whereas Cd distributed in associated with the cathode electrode, catholyte and electrochemically active bacteria was quantitatively calculated. As the reduction of Cd (?), adsorbed total Cd content on electrode increases gradually, total Cd content in catholyte gradually rdecreases, total Cd content in becteria first increases and then decreases. After 5 h, adsorbed total Cd content account for most of the whole.