Based on the four indigenous electrotrophs (Stenotrophomonas maltophilia JY1, Citrobacter sp. JY3, Pseudomonas aeruginosa JY5 and Stenotrophomonas sp. JY6) isolated from well adapted Cu(II)-reduced biocathodes of microbial fuel cells (MFCs), a rhodamine based Cu(II) fluorescent probe was used to imaginably and quantitatively track subcellular Cu(II) ions in these electrotrophs. Cathodic electrons led to more Cu(II) ions (14.3-30.1%) in the intracellular sites at operation time of 2-3 h with Cu(II) removal rates of 2.90-3.64 mg/L h whereas the absence of cathodic electrons prolonged the appearance of more Cu(II) ions (16.6-22.5%) to 5 h with Cu(II) removal rates of 1.96-2.28 mg/L h. This study illustrates that cathodic electrons directed more Cu(II) ions for quicker entrance into the electrotrophic cytoplasm, and gives an alternative approach for developing imaging and functionally tracking Cu(II) ions in the electrotrophs of MFCs. (C) 2016 Elsevier Ltd. All rights reserved.