STUDIES ON DIVISION INHIBITION AND FILAMENT FORMATION OF ESCHERICHIA COLI BY ULTRAVIOLET LIGHT

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Abstract
A quantitative micro-scopic assay is used to study the effect of small doses of monochromatic UV light on the cellular division of E coli strain B. Abnormally long cells called "filaments" are formed as a result of the UV-induced division delay. This division inhibition is specific in that division stops while total mass, ribonucleic acid, and deoxyribonucleic acid synthesis continue at the same rate as for dividing cells. The UV survival curves for division ability are single-hit and the 37% survival dose is 3 ergs/mm2 at 2652 A. Many of these filaments recover the ability the divide at some later time and form normal-appearing macroscopic colonies on nutrient agar. The UV action spectrum for division inhibition has a peak at 2650 A and suggests nucleic acid as the absorbing cell component active in initiating the delay. The division inhibition can be partially reversed by visible light if given within 20 minutes after the UV exposure. The filaments appear to be single cells with many "nuclear bodies" and not segmented structures or chains of cells.