Ultraviolet Radiation Studies of FilamentousEscherichia coliB

Abstract

Sirall ultraviolet (UV) doses caused E. coli B to grow into long filamentous single cells. A large fraction of these filaments can recover their division ability and can form colonies under appropriate conditions. Preformed filaments can be irradiated with UV, and their ability to still produce colonies can be compared with that of irradiated normal cells. In this regard, filaments are more sensitive to UV than normal cells. Filaments can still host-cell reactivate UV-irradiated Tl phage and can regain their own deoxyri-bonucleic-acid (DNA) synthetic ability after it has been blocked by UV. This indicates that these filaments still retain mechanisms for repairing UV-damaged DNA. Pantoyl lactone, an agent that stimulates cell-division recovery in UV-irradiated E. coli B, causes increased UV resistance for both normal and filamentous cells, with the filaments becoming more resistant than normal cells. In the absence of pantoyl lactone, irradiated filaments grow to a length of about 50 times normal and then stop growing. These long filaments cannot subsequently divide and give colonies. We conclude that the UV dose given to the performed filaments caused an additional division lag beyond that of unirradiated filaments, and that some critical length is reached after which division recovery and colony formation is impossible. Irradiated normal cells recover before reaching this critical length.