{'fraction_non_alphanumeric': 0.019071310116086235, 'fraction_numerical': 0.029850746268656716, 'mean_word_length': 4.975247524752476, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
AN ACTION SPECTRUM FOR ULTRAVIOLET RADIATION‐INDUCED MEMBRANE DAMAGE IN Escherichia coli K‐12

A wild‐type Escherichia coli K‐12 strain was irradiated using monochromatic radiation in the range 254 to 405 nm. A measure of the cell membrane damage induced at each wavelength was investigated by comparing cell viability after irradiation on nutrient agar and on minimal medium containing either a low or high inorganic salt concentration. An action spectrum for lethality and for cell membrane damage was then determined. From 254 to 310 nm lethality closely corresponded to the absorption spectrum of DNA, and there was no indication of membrane damage. However, above a wavelength of 310 nm, the direct absorption of radiation by DNA could not account for the sensitivity observed. Moreover, at wavelengths longer than 310 nm, cell membrane damage was induced and by an increasing factor up to a peak at 334 nm. At the longer wavelengths of 365 and 405 nm, there was a gradual decrease from the peak of damage to cell membranes induced by 334 nm radiation. These results indicate that cell membrane damage may contribute significantly to near‐UV radiation‐induced cell lethality in wild‐type E. coli K‐12.