Many bacteria, including E. coli, are capable of growing under both anaerobic and aerobic conditions. Some mutations are introduced into an E. coli strain that inactivate several enzymes involved in DNA repair. The mutant strain grows normally when kept in an incubator with a 100% nitrogen gas atmosphere. However, the strain dies when exposed to a normal laboratory atmosphere. Why

Due to inability to survive in aerobic condition.

Explanation:

The strain dies when exposed to a normal laboratory atmosphere instead of nitrogen gas atmosphere because the mutation causes change in the capability of the strain to survive in the aerobic conditions. This mutation inactivate several enzymes which is also responsible for their capabilities of surviving under both anaerobic and aerobic environment so that's why the strain dies when exposed to normal atmosphere..