Global transcriptomic analysis via RNA-seq is often hampered by the high abundance of ribosomal (r)RNA in bacterial cells. To remove rRNA and enrich coding sequences, subtractive hybridization procedures have become the approach of choice prior to RNA-seq, with their efficiency varying in a manner dependent on sample type and composition. Yet, despite an increasing number of RNA-seq studies, comparative evaluation of bacterial rRNA depletion methods has remained limited. Moreover, no such study has utilized RNA derived from bacterial biofilms, which have potentially higher rRNA:mRNA ratios and higher rRNA carryover during RNA-seq analysis.
Binghamton University researchers evaluated the efficiency of three subtractive hybridization-based kits in depleting rRNA from samples derived from biofilm, as well as planktonic cells of the opportunistic human pathogen Pseudomonas aeruginosa. Their results indicated different rRNA removal efficiency for the three procedures, with the Ribo-Zero kit yielding the highest degree of rRNA depletion, which translated into enhanced enrichment of non-rRNA transcripts and increased depth of RNA-seq coverage. The results indicated that, in addition to improving RNA-seq sensitivity, efficient rRNA removal enhanced detection of low abundance transcripts via qPCR.
Quantitative and qualitative comparison of RNA recovered following rRNA depletion
A total of 4 μg of DNAse-treated RNA, isolated form 3-day-old P. aeruginosa PAO1 biofilms, was subjected to treatment with the Illumina Ribo-Zero rRNA Removal Kit (Bacteria), Ambion MICROBExpress™ Bacterial mRNA Enrichment Kit and the Life Technologies RiboMinus Transcriptome Isolation Kit, Bacteria. Following rRNA depletion and ethanol/acetate precipitation and resuspension in equal volumes of water, the RNA was assessed using Qubit fluorimetric quantitation with the Qubit RNA HS Assay Kit. Yields are reported as total RNA recovered (A) and as percentage of the input RNA (B). The RNA samples were also assessed using the Bioanalyzer RNA 6000 Pico kit. Representative electropherograms of (C) starting total RNA material and aliquots of the RNA samples that have been processed using the (D) MICROBExpress, (E) RiboMinus, or (F) Ribo-Zero kits are shown. Dashed lines indicate peaks corresponding to 16S and 23S RNA traces, which were detected in total RNA, MICROBExpress, and RiboMins samples. (G) The area of 16S and 23S rRNA peaks as percent of the total detected RNA was estimated, as determined using the 2100 Expert Software. RFU, relative fluorescence units. Experiments were repeated using three biological replicates.