DNA passes between microorganisms

Although the Bacteria lack the sophisticated systems of sexual reproduction found in eukaryotes, they do not rely on mutation alone to generate diversity within their populations. Spontaneous mutagenesis alone is insufficient to respond to the varying environments that the majority of Bacterial species encounter. Bacteria can acquire variation in genes, complete new genes or even complete biosynthetic pathways via the acquisition of plasmids infection by bacteriophages or transposons and through direct nonsexual interchange of genetic information.

The phenomenon of Bacterial transfer of genetic information has long been studied in the context of same-species or vertical gene transfer.  However, it has become increasingly apparent that transfer occurs among species too.  Horizontal gene transfer can account for the rapid spread of antibiotic resistance in a variety of hospital-acquired infections but also can be used to our advantage in the generation of consortia for the biodegradation of xenobiotics. In a mixed  population like as that found in a hospital or bioreactor it is hard to pinpoint the exact mechanisms used to acquire DNA but looking in the genomes of isolated organisms it can be easy to pinpoint the genomic regions which originated in other organisms through their unusual codon usage or other sequence signatures.

The best understood mechanism of gene transfer is conjugation a technique which gave the first genetic map of Escherichia coli. This is a plasmid-mediated effect in contrast to transduction in that DNA moves from the donor to the recipient strains through means of a Bacterial virus or bacteriophage. The method used most generally to introduce foreign genes into laboratory strains of Bacteria is transformation a poorly understood process relying on a shock response to take up plasmids or other fragments of DNA.