Single Molecular Real Time Research Articles

Abstract 1159: Single molecule sequencing to detect and characterize somatic mutations in cancer genomes

Abstract One result of large-scale cancer genome characterization is the identification of sets of genes that are commonly mutated in specific tumor types or subtypes and have clinical relevance, e.g. are prognostic or diagnostic. In this paradigm, we have investigated the use of a novel, single molecular real time (SMRT) sequencing technology from Pacific Biosciences that enables targeted regions to be sequenced in real time as single molecules in a mixed population. Several experiments were performed to evaluate the performance of this technology in the context of testing for cancer-specific mutations in previously characterized samples. In the first experiment we assessed whether SMRT sequencing could detect the known mutations of PCR products derived from genomic DNA of tumor cells compared to normal cells. In the second experiment we investigated the impact of different neoplastic cellularity percentages on the ability to detect known mutations. The final experiment involved producing deep read count SMRT sequencing data from PCR products containing known variants to ascertain their different levels of prevalence in a discrete tumor cell population, and then comparing these results to deep read counts for the same variants obtained with the Illumina instrument. Our results indicate that the Pacific Biosciences instrument offers exquisite sensitivity and speed in detecting somatic single base mutations in tumor-derived genomic DNAs. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 1159.

MP073 Host-cell responses in models of persistent C. pneumoniae infection

A key to persistent and recurrent Staphylococcus aureus infections is its ability to adapt to diverse and toxic conditions. This ability includes a switch into a biofilm or to the quasi-dormant Small Colony Variant (SCV). The development and molecular attributes of SCVs have been difficult to study due to their rapid reversion to their parental cell-type. We recently described the unique induction of a matrix-embedded and stable SCV cell-type in a clinical S. aureus strain (WCH-SK2) by growing the cells with limiting conditions for a prolonged timeframe. Here we further study their characteristics. They possessed an increased viability in the presence of antibiotics compared to their non-SCV form. Their stability implied that there had been genetic changes; we therefore determined both the genome sequence of WCH-SK2 and its stable SCV form at a single base resolution, employing Single Molecular Real-Time (SMRT) sequencing that enabled the methylome to also be determined. The genetic features of WCH-SK2 have been identified; the SCCmec type, the pathogenicity and genetic islands and virulence factors. The genetic changes that had occurred in the stable SCV form were identified; most notably being in MgrA, a global regulator, and RsbU, a phosphoserine phosphatase within the regulatory pathway of the sigma factor SigB. There was a shift in the methylomes of the non-SCV and stable SCV forms. We have also shown a similar induction of this cell-type in other S. aureus strains and performed a genetic comparison to these and other S. aureus genomes. We additionally map RNAseq data to the WCH-SK2 genome in a transcriptomic analysis of the parental, SCV and stable SCV cells. The results from this study represent the unique identification of a suite of epigenetic, genetic and transcriptional factors that are implicated in the switch in S. aureus to its persistent SCV form.