Cells were harvested from the anode via centrifugation (4℃, 8000 rpm, 7741 × g, Avanti J26S XP, 30 min), which were immediately frozen in liquid nitrogen. The RNAprep pure Cell/Bacteria Kit (TIANGEN) was used to extract the total RNA The NEBNext®UltraTM RNA Library Prep Kit for Illumina® (NEB, USA) was used to construct the sequencing libraries, in which each sample was modified with the index codes. The index-coded samples were clustered using the TruSeq PE Cluster Kit v3-cBot-HS (Illumina) on a cBot Cluster Generation System