BS-Seq/Bisulfite-seq/WGBS

BS-Seq/Bisulfite-seq/WGBS

Bisulfite sequencing (BS-Seq) or whole-genome bisulfite sequencing (WGBS) is a well-established protocol to detect methylated cytosines in genomic DNA . In this method, genomic DNA is treated with sodium bisulfite and then sequenced, providing single-base resolution of methylated cytosines in the genome. Upon bisulfite treatment, unmethylated cytosines are deaminated to uracils which, upon sequencing, are converted to thymidines. Simultaneously, methylated cytosines resist deamination and are read as cytosines. The location of the methylated cytosines can then be determined by comparing treated and untreated sequences. Bisulfite treatment of DNA converts unmethylated cytosines to thymidines, leading to reduced sequence complexity. Very accurate deep sequencing serves to mitigate this loss of complexity.

Pros:
  • CpG and non-CpG methylation throughout the genome is covered at single-base resolution
  • 5mC in dense, less dense, and repeat regions are covered
Cons:
  • Bisulfite converts unmethylated cytosines to thymidines, reducing sequence complexity, which can make it difficult to create alignments
  • NPs where a cytosine is converted to thymidine will be missed upon bisulfite conversion
  • Bisulfite conversion does not distinguish between 5mC and 5hmC