title: 16S rRNA transcriptome data from borehole DUSEL 3A and in situ electrochemical colonization (ISEC) incubations at Sanford Underground Research Facility
design: Total RNA was extracted from the filters and electrode-attached biofilms via physical (freeze, thaw, vortex), chemical (sodium dodecyl sulfate and EDTA), and biological (lysozyme) disruption of the cell wall prior to phenol-chloroform extraction. A control that included only reagents and no sample material was extracted alongside the samples to confirm lack of contamination. Any residual DNA was digested using TURBO DNA-free TM Kit (ThermoFisher Scientific, USA) and verified to be free of DNA by running a PCR of the RNA extraction. Samples were reverse transcribed with MMLV (Promega, USA) using 806R primer. The complementary DNA (cDNA) of each sample was sent to Molecular Research DNA (Shallowater, TX, USA) for library preparation and high throughput sequencing. Sequencing library preparation included amplifying the hypervariable region V4 of the bacterial 16S rRNA transcript using barcoded fusion primers 515F and 806R, according to previously described methods. Following amplification, all PCR products from different samples were mixed in equal concentrations and purified using Agencourt Ampure beads (Agencourt Bioscience Corporation, MA, USA). Samples were sequenced on Roche 454 FLX titanium platform using recommended reagents and following manufacturers guidelines.