Project description:Bisulfite sequencing is a valuable tool for mapping the position of 5-methylcytosine in the genome at single base resolution. However, the associated chemistry renders the majority of DNA fragments unsequenceable, thus necessitating PCR amplification. Furthermore, bisulfite conversion generates an A,T-rich DNA library that leads to major PCR biases that may confound methylation analysis. Here we report a method that enables accurate methylation analysis, by rebuilding the damaged DNA library after bisulfite treatment. This recovery after bisulfite treatment (ReBuilT) approach enables PCR-free bisulfite sequencing from low nanogram quantities of genomic DNA. We applied the ReBuilT method for whole methylome analysis of the A,T rich genome of Plasmodium berghei. We demonstrate substantial improvements in coverage and the reduction of sequence-context biases as compared to classical methylome analysis. Our method will be widely applicable for accurate, quantitative methylation analysis, even for technically challenging genomes, and where limited sample DNA is available. From the same DNA sample we prepared 3 PCR-free Bisulfite-Seq replicates (ReBuilT) and 2 standard Bisulfite-Seq replicates (PCR-BS).
Project description:Five hundred nanograms of genomic DNA was fragmented by Covaris S2, the fragmented DNAs were performed end-repair, A-tailing at the 3 prime end, adaptors ligation with an IDT dual-indexed UMI adaptor system at the terminal ends. The adapter ligated library with size range 300-750bp were selected by dual-SPRI method. Twenty percent of the size selected PCR-free libraries were enriched by 5 PCR cycles prior to library size assessment by Bioanalyzer Fragment Analyzer. The PCR-free libraries were quantified by qPCR.The PCR-free libraries were denatured and diluted to optimal concentration. Illumina NovaSeq 6000 was used for Pair-End 151bp sequencing.
Project description:As transposon sequencing (TnSeq) assays have become prolific in the microbiology field, it is of interest to scrutinize their potential drawbacks. TnSeq results are determined by counting transposon insertions following the PCR-based enrichment and subsequent deep sequencing of transposon insertions. Here we explore the possibility that PCR amplification of transposon insertions in a TnSeq library skews the results by introducing bias into the detection and/or enumeration of insertions. We compared the detection and frequency of mapped insertions when altering the number of PCR cycles in the enrichment step. In addition, we devised and validated a novel, PCR-free TnSeq method where the insertions are enriched via CRISPR/Cas9-targeted transposon cleavage and subsequent Oxford Nanopore sequencing. These PCR-based and PCR-free experiments demonstrate that, overall, PCR amplification does not significantly bias the results of the TnSeq assay insofar as insertions in the majority of genes represented in our library were similarly detected regardless of PCR cycle number and whether or not PCR amplification was employed. However, the detection of a small subset of genes which had been previously described as essential is indeed sensitive to the number of PCR cycles. We conclude that PCR-based enrichment of transposon insertions in a TnSeq assay is reliable but researchers interested in profiling essential genes should carefully weigh the number of amplification cycles employed in their library preparation protocols. In addition, we present a PCR-free TnSeq alternative that is comparable to traditional PCR-based methods although the latter remain superior owing to their accessibility and high sequencing depth.
Project description:High-resolution detection of genome-wide 5-hydroxymethylcytosine (5hmC) sites of small-scale samples represents a continuous challenge. Here, we present CATCH-seq, a bisulfite-free, base-resolution method for the genome-wide detection of 5hmC. CATCH-seq is based on selective 5hmC oxidation, labeling and subsequent C-to-T transition during PCR. Applications of CATCH-seq to nano-scale DNA samples reveal previously underappreciated non-CG 5hmCs in the hESC genome and base-resolution hydroxymethylome in human cell-free DNA.