Genome Capture Sequencing Selectively Enriches Bacterial DNA and Enables Genome-Wide Measurement of Intrastrain Genetic Diversity in Human Infections

Abstract

ABSTRACT Within-host evolution produces genetic diversity in bacterial strains that cause chronic human infections. However, the lack of facile methods to measure bacterial allelic variation in clinical samples has limited understanding of intrastrain diversity’s effects on disease. Here, we report a new method termed genome capture sequencing (GenCap-Seq) in which users inexpensively make hybridization probes from genomic DNA or PCR amplicons to selectively enrich and sequence targeted bacterial DNA from clinical samples containing abundant human or nontarget bacterial DNA. GenCap-Seq enables accurate measurement of allele frequencies over targeted regions and is scalable from specific genes to entire genomes, including the strain-specific accessory genome. The method is effective with samples in which target DNA is rare and inhibitory and DNA-degrading substances are abundant, including human sputum and feces. In proof-of-principle experiments, we used GenCap-Seq to investigate the responses of diversified Pseudomonas aeruginosa populations chronically infecting the lungs of people with cystic fibrosis to in vivo antibiotic exposure, and we found that treatment consistently reduced intrastrain genomic diversity. In addition, analysis of gene-level allele frequency changes suggested that some genes without conventional resistance functions may be important for bacterial fitness during in vivo antibiotic exposure. GenCap-Seq’s ability to scalably enrich targeted bacterial DNA from complex samples will enable studies on the effects of intrastrain and intraspecies diversity in human infectious disease. IMPORTANCE Genetic diversity evolves in bacterial strains during human infections and could affect disease manifestations and treatment resistance. However, the extent of diversity present in vivo and its changes over time are difficult to measure by conventional methods. We developed a novel approach, GenCap-Seq, to enrich microbial DNA from complex human samples like sputum and feces for genome-wide measurements of bacterial allelic diversity. The approach is inexpensive, scalable to encompass entire targeted genomes, and works in the presence of abundant untargeted nucleic acids and inhibiting substances. We used GenCap-Seq to investigate in vivo responses of diversified bacterial strains to antibiotic treatment. This method will enable new ideas about the effects of intrastrain diversity on human infections to be tested.

Keywords

• evolution
• genetic diversity
• genomics
• infection
• microbiology
• targeted enrichment