Imaging and distribution of Cd(II) ions in electrotrophs and its response to current and electron transfer inhibitor in microbial electrolysis cells

- Cd(II) fluorescent probe imaginably sensed Cd(II) ions in electrotrophs.
- Various forms of cadmium in electrotrophs responded to current and 2,4-dinitrophenol.
- Current directed Cd(II) ions for import and export via electrotrophic cell membrane.
- 2,4-DNP inhibited Cd(II) ions import and export via electrotrophic membrane.
- Total cadmium in catholyte and electrotrophs was independent of 2,4-DNP.

Biocathode microbial electrolysis cells (MECs) with electrotrophs on the cathodes are proved to be attractive for Cd(II) removal with simultaneous hydrogen production. However, the underlying roles of current and electron transfer inhibitor of 2,4-dinitrophenol (2,4-DNP) in the distribution of dissolved Cd(II) ions in the electrotrophs are largely unknown. Based on four indigenous electrotrophs (Ochrobactrum sp X1, Pseudomonas sp X3, Pseudomonas delhiensis X5 and Ochrobactrum anthropi X7) isolated from well developed Cd(II)-removal biocathodes of MECs, a quinoline-based Cd(II) fluorescent probe was used to imaginably and quantitatively map Cd(II) ions in electrotrophs, and its response to current and 2,4-DNP in MECs. 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. In terms of total cadmium, current always directed less cadmium in catholyte and electrotrophs with independence of the presence of 2,4-DNP. This study gives an alternative approach for developing imaging and mapping Cd(II) ions in the electrotrophs, and thus benefits for clarifying the roles of current and 2,4-DNP in electrotrophic removal of Cd(II) ions from catholyte in MECs.