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.

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wild parsnip is a perennial plant which reproduces rapidly in areas which have no sign of agricultural activity such roadside or at no tillage open areas. it's considered invasive because it can inhibit the growth of another plant  and its reproduction is fast. there are several harmful effects of this invasive plant although its taproot is edible since it is a member of the carrot family. wild parsnips can cause skin blistering when in contact because of the chemicals it contains, second it inhibits the growth of other plants, it will restrict the growth of animals when eaten and lastly, it drives away natural pollinators like bees.