The gene transfer agent (GTA) is a bacteriophage-like particle that transfers genomic DNA from a donor to a recipient bacterium. The Rhodobacter capsulatus GTA (RcGTA) was the first to be studied and this protocol has been optimized for RcGTA transduction, although it could be modified for other bacteria containing a GTA. The RcGTA transduction assay can be used to determine transduction efficiencies, to create gene knock-outs, or to create new strains by transferring alleles from one strain to another.