Abstract: Described herein is a method for isolating microbial DNA from a sample that comprises host DNA and microbial DNA. In some embodiments, the method may comprise: obtaining a tagged DNA sample, wherein the tagged DNA sample contains host DNA and microbial DNA, both comprising an appended universal adaptor; b) hybridizing the extracted DNA, in solution, with affinity-tagged RNA probes generated by in vitro transcribing, in the presence of an affinity-tagged ribonucleotide, a library of fragmented host DNA that has been ligated to an RNA promoter adaptor; c) binding the product of step b) with a capture agent that is tethered to a substrate, in the presence of RNA oligonucleotides that are complementary to or have the same sequence as one or more strands of the universal adaptor, thereby capturing the host DNA on the substrate; and d) collecting the unbound DNA, wherein the unbound DNA comprises the microbial DNA.