The invention provides a genetic tool to insert, replace, delete, or otherwise manipulate a nucleic acid sequence in a microorganism to produce a recombinant microorganism. Notably, the invention makes use of homologous recombination, a type of genetic recombination in which nucleotide sequences are exchanged between two similar or identical molecules of DNA. Since the invention involves three homologous recombination events, it is referred to as a “triple cross” method.