Long read sequencing and de novo assembly of Hepatitis B Virus identifies 5mCpG in CpG islands

Hepatitis B Virus (HBV) is a 3.2KB DNA virus that causes acute and chronic hepatitis. HBV infection is a world health problem, with 350 million chronically infected people at increased risk of developing liver disease and hepatocellular carcinoma (HCC). Methylation of HBV DNA in a CpG context (5mCpG) can alter the expression patterns of viral genes related to infection and cellular transformation. Moreover, it may also provide clues to why certain infections are cleared, or persist with or without progression to cancer. The detection of 5mCpG often requires techniques that damage DNA or introduce bias through a myriad of limitations. Therefore, we developed a method for the detection of 5mCpG on the HBV genome that does not rely on bisulfite conversion or PCR. With cas9 guided RNPs to specifically target the HBV genome, we enriched in HBV DNA from Primary Human Hepatocytes (PHH) infected with different HBV genotypes, as well as enriching in HBV from infected patient liver tissue; followed by sequencing with Oxford Nanopore Technologies MinION. Detection of 5mCpG by Nanopore sequencing was benchmarked with Bisulfite-quantitative Methyl Specific PCR (BS-qMSP). 5mCpG levels in HBV determined by BS-qMSP and Nanopore sequencing were highly correlated. Our Nanopore sequencing approach achieved a coverage of [~]2000x of HBV depending on infection efficacy, sufficient coverage to perform a de novo assembly and detect small fluctuations in HBV methylation, providing the first de novo assembly of native HBV DNA, as well as the first landscape of 5mCpG from native HBV sequences. Moreover, by capturing entire HBV genomes, we explored the epigenetic heterogeneity of HBV in infected patients and identified 4 epigenetically distinct clusters based on methylation profiles. This method is a novel approach that enables the enrichment of viral DNA in a mixture of nucleic acid material from different species and will serve as a valuable tool for infectious disease monitoring.