Recombinant bacteria are bacteria that have undergone genetic engineering. This means their DNA has been altered by the introduction of new DNA. Such bacteria have been of immense value in biological research, and for industrial and environmental uses.
New DNA is often introduced in some sort of vehicle that is known as a vector. This can be a plasmid or a virus. The plasmid has a type of selectable marker, so that the cells will keep producing it. Often, this is antibiotic resistance. It is also possible to introduce a gene directly into the bacterium’s own DNA.