Sample and Library Preparation for PacBio Long-Read Sequencing in Grapevine

PacBio long-read sequencing is a third-generation technology that generates long reads up to 20 kilobases (kb), unlike short-read sequencing instruments that produce up to 600 bases. Long-read sequencing is particularly advantageous in higher organisms, such as humans and plants, where repetitive regions in the genome are more abundant. The PacBio long-read sequencing uses a single molecule, real-time approach where the SMRT cells contain several zero-mode waveguides (ZMWs). Each ZMW contains a single DNA molecule bound by a DNA polymerase. All ZMWs are flushed with deoxy nucleotides with a fluorophore specific to each nucleotide. As the sequencing proceeds, the detector detects the wavelength of the fluorescence and the nucleotides are read in real-time. This chapter describes the sample and library preparation for PacBio long-read sequencing for grapevine.

Rational development of transformation in Clostridium thermocellum ATCC 27405 via complete methylome analysis and evasion of native restriction-modification systems

A major barrier to both metabolic engineering and fundamental biological studies is the lack of genetic tools in most microorganisms. One example is Clostridium thermocellum ATCC 27405^T, where genetic tools are not available to help validate decades of hypotheses. A significant barrier to DNA transformation is restriction–modification systems, which defend against foreign DNA methylated differently than the host. To determine the active restriction–modification systems in this strain, we performed complete methylome analysis via single-molecule, real-time sequencing to detect 6-methyladenine and 4-methylcytosine and the rarely used whole-genome bisulfite sequencing to detect 5-methylcytosine. Multiple active systems were identified, and corresponding DNA methyltransferases were expressed from the Escherichia coli chromosome to mimic the C. thermocellum methylome. Plasmid methylation was experimentally validated and successfully electroporated into C. thermocellum ATCC 27405. This combined approach enabled genetic modification of the C. thermocellum-type strain and acts as a blueprint for transformation of other non-model microorganisms.

Validation of intra- and inter-laboratory reproducibility of the Xpert HPV assay according to the international guidelines for cervical cancer screening

Background

Cervical cancer screening with assays detecting DNA of high-risk human papillomavirus (hrHPV) types is more effective than cytology-based screening. This study completes the diagnostic accuracy assessment conducted previously within the framework of VALGENT-2 (Validation of HPV genotyping Tests) and aims to determine whether the reproducibility of Xpert HPV is in line with international validation criteria.

Methods

Validation of new hrHPV DNA assays requires demonstration of good reproducibility and non-inferior clinical accuracy for cervical precancer compared to a standard comparator assay. The international reproducibility criteria are: lower bound of 95% confidence interval of the intra- and inter-laboratory agreement regarding detection of high-risk HPV DNA exceeding 87% with kappa ≥0.5.

Results

The Xpert HPV assay showed high intra-laboratory reproducibility with an overall positivity/negativity agreement of 96.9% and a kappa of 0.925. Inter-laboratory testing showed an agreement of 97.8% with a kappa of 0.948.

Conclusions

The Xpert HPV assay fulfills the HPV test reproducibility criterion requirement for use in cervical cancer screening.