We report the discovery of morphologically diverse biofilms growing under redox-transposed conditions, at the interface of oxidant-bearing seeps or rivulets discharging into the dark euxinic bottom waters of a meromictic lake.
The V4 hypervariable region of the 16S rRNA gene was amplified using the original Earth Microbiome Project barcoded primers 515F (5-GTGCCAGCMGCCGCGGTAA-3) and 806R (5-GGACTACHVGGGTWTCTAAT-3)  and Illumina flow cell adapter sequences at the Environmental Sample Preparation and Sequencing Facility (ESPSF) at Argonne National Laboratory. PCR amplifications were done in triplicate. PCR products were purified and aliquoted proportionately into a single pool and diluted to 2 nM, denatured, and further diluted to 6.1 pM with a 30% PhiX spike for sequencing on the Illumina MiSeq platform.  On average 60,000 reads (253 bp) were obtained per sample following removal of singletons. Phylogenetic and taxonomic analyses were performed using QIIME v.1.8.0 and the Greengenes 13_8 taxonomy.