Why must genetically altered bacteria be grown in a carefully controlled environment?

Genetically modified organisms (GMOs) are widely used in research and for making pharmaceuticals and other products. However, use of genetically modified bacteria outside of the lab has been limited by concerns that they—and the sometimes novel genes they carry—could escape into the wild.

Scientists have attempted to solve this problem in a variety of ways, including the creation of bacteria that depend on nutrients they can’t make themselves. But these bacteria might survive in the wild by receiving those nutrients from natural organisms.

Not only have GMO crops not improved yields, they have vastly increased the use of glyphosate, the active ingredient in Monsanto's Roundup herbicide. ... The explosion in glyphosate use is not only bad for farmers' health, it's also bad for the environment, especially for certain birds, insects and other wildlife.

Genetic Contamination/Interbreeding

Introduced GMOs may interbreed with the wild-type or sexually compatible relatives. The novel trait may disappear in wild types unless it confers a selective advantage to the recipient. However, tolerance abilities of wild types may also develop, thus altering the native species’ ecological relationship and behaviour.