Evaluating the Benefits and Limits of Multiple Displacement Amplification With Whole-Genome Oxford Nanopore Sequencing.

Abstract

Multiple displacement amplification (MDA) outperforms conventional PCR in long fragment and whole-genome amplification, making it attractive to couple MDA with long-read sequencing of samples with limited quantities of DNA to obtain improved genome assemblies. Here, we explore the efficacy and limits of MDA for efficient low-cost genome sequence assembly using Oxford Nanopore Technologies (ONTs) rapid library preparations and minION sequencing. We successfully generated almost complete genome sequences for all organisms examined, including Gram-positive (Staphylococcus aureus, Enterococcus faecium) and Gram-negative (Escherichia coli) prokaryotes and one challenging eukaryotic pathogen (Cryptosporidium spp) representing a broad spectrum of critical infectious disease pathogens. High-quality data from those samples were generated starting with only 0.025 ng of total DNA. Controlled sheared DNA samples exhibited a distinct pattern of size increase after MDA, which may be associated with the amplification of long, low-abundance fragments present in the assay, as well as generating concatemeric sequences during amplification. To address concatemers, we developed a computational pipeline (CADECT: Concatemer Detection Tool) to identify and remove putative concatemeric sequences. This study highlights the efficacy of MDA in generating high-quality genome assemblies from limited amounts of input DNA. Also, the CADECT pipeline effectively mitigated the impact of concatemeric sequences, enabling the assembly of contiguous sequences even in cases where the input genomic DNA was degraded. These results have significant implications for the study of organisms that are challenging to culture in vitro, such as Cryptosporidium, and for expediting critical results in clinical settings with limited quantities of available genomic DNA.