Separation of single-stranded DNA, double-stranded DNA and RNA from an environmental viral community using hydroxyapatite chromatography.

Viruses, particularly bacteriophages (phages), are the most numerous biological entities on Earth. Viruses modulate host cell abundance and diversity, contribute to the cycling of nutrients, alter host cell phenotype, and influence the evolution of both host cell and viral communities through the lateral transfer of genes. Numerous studies have highlighted the staggering genetic diversity of viruses and their functional potential in a variety of natural environments. Metagenomic techniques have been used to study the taxonomic diversity and functional potential of complex viral assemblages whose members contain single-stranded DNA (ssDNA), double-stranded DNA (dsDNA) and RNA genotypes. Current library construction protocols used to study environmental DNA-containing or RNA-containing viruses require an initial nuclease treatment in order to remove nontargeted templates. However, a comprehensive understanding of the collective gene complement of the virus community and virus diversity requires knowledge of all members regardless of genome composition. Fractionation of purified nucleic acid subtypes provides an effective mechanism by which to study viral assemblages without sacrificing a subset of the community's genetic signature. Hydroxyapatite, a crystalline form of calcium phosphate, has been employed in the separation of nucleic acids, as well as proteins and microbes, since the 1960s. By exploiting the charge interaction between the positively-charged Ca(2+) ions of the hydroxyapatite and the negatively charged phosphate backbone of the nucleic acid subtypes, it is possible to preferentially elute each nucleic acid subtype independent of the others. We recently employed this strategy to independently fractionate the genomes of ssDNA, dsDNA and RNA-containing viruses in preparation of DNA sequencing. Here, we present a method for the fractionation and recovery of ssDNA, dsDNA and RNA viral nucleic acids from mixed viral assemblages using hydroxyapatite chromatography.