Why do the bacteria used in recombinant DNA expirements have been changed so that they can only survive under special conditions in a laboratory?

Your grammar for this question is not very good however, I believe I can answer your question.

If they do get change so they can only survive in a certain condition in a laboratory, I would most likely be to make the bacteria not able to survive Outside the lab. In other words, they don't want it getting out. This would be because they usually give the bacteria a resistance to certain antibacterial solutions so that when they cultivate he bacteria, the bacteria that did not accept the plasmid will die from the antibiotic that got mixed into the Agar. In other words, the only bacteria that would grow are the bacteria have accepted the plasmid.