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This article is part of the supplement: The International Conference on Intelligent Biology and Medicine (ICIBM): Systems Biology

Open Access Research

Optimizing hybrid assembly of next-generation sequence data from Enterococcus faecium: a microbe with highly divergent genome

Yajun Wang1, Yao Yu2, Bohu Pan2, Pei Hao4, Yixue Li1, Zhifeng Shao1, Xiaogang Xu3* and Xuan Li2*

Author Affiliations

1 Shanghai Center for Systems Biomedicine, Shanghai Jiaotong University, Shanghai 200240, China

2 Key Laboratory of Synthetic Biology, Institute of Plant Physiology and Ecology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200032, China

3 Institute of Antibiotics, Huashan Hospital of Fudan University, Shanghai 200040, China

4 Institut Pasteur of Shanghai, Chinese Academy of Science, Shanghai 200025, China

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BMC Systems Biology 2012, 6(Suppl 3):S21  doi:10.1186/1752-0509-6-S3-S21

Published: 17 December 2012

Abstract

Background

Sequencing of bacterial genomes became an essential approach to study pathogen virulence and the phylogenetic relationship among close related strains. Bacterium Enterococcus faecium emerged as an important nosocomial pathogen that were often associated with resistance to common antibiotics in hospitals. With highly divergent gene contents, it presented a challenge to the next generation sequencing (NGS) technologies featuring high-throughput and shorter read-length. This study was designed to investigate the properties and systematic biases of NGS technologies and evaluate critical parameters influencing the outcomes of hybrid assemblies using combinations of NGS data.

Results

A hospital strain of E. faecium was sequenced using three different NGS platforms: 454 GS-FLX, Illumina GAIIx, and ABI SOLiD4.0, to approximately 28-, 500-, and 400-fold coverage depth. We built a pipeline that merged contigs from each NGS data into hybrid assemblies. The results revealed that each single NGS assembly had a ceiling in continuity that could not be overcome by simply increasing data coverage depth. Each NGS technology displayed some intrinsic properties, i.e. base calling error, systematic bias, etc. The gaps and low coverage regions of each NGS assembly were associated with lower GC contents. In order to optimize the hybrid assembly approach, we tested with varying amount and different combination of NGS data, and obtained optimal conditions for assembly continuity. We also, for the first time, showed that SOLiD data could help make much improved assemblies of E. faecium genome using the hybrid approach when combined with other type of NGS data.

Conclusions

The current study addressed the difficult issue of how to most effectively construct a complete microbial genome using today's state of the art sequencing technologies. We characterized the sequence data and genome assembly from each NGS technologies, tested conditions for hybrid assembly with combinations of NGS data, and obtained optimized parameters for achieving most cost-efficiency assembly. Our study helped form some guidelines to direct genomic work on other microorganisms, thus have important practical implications.