Such micro-organisms are being designed for agricultural purposes such as extending the range of plants which harbour nitrogen-fixing bacteria in their roots. Release of such organisms creates the risk that once released they may exhibit some previously unknown pathogenicity, might take over from some naturally occurring bacteria (possibly having other positive functions which thus are lost) or pass on some unwanted trait to such indigenous bacteria. There is also concern that an uncontrolled genetic mutation could produce, from such an engineered micro-organism, a form with hazardous consequences for the environment.
Genetically engineered micro-organisms were under trial in 1989. None are as yet known to have been deliberately released.