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LETHAL PHOTOSENSITIZATION OF MICROORGANISMS WITH LIGHT FROM A CONTINUOUS‐WAVE GAS LASER
Author(s) -
Macmillan James D.,
Maxwell W. Andrew,
Chichester C. O.
Publication year - 1966
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1111/j.1751-1097.1966.tb09845.x
Subject(s) - toluidine , microbiology and biotechnology , methylene blue , rhodotorula , biology , escherichia coli , bacteria , yeast , chemistry , biochemistry , genetics , photocatalysis , gene , catalysis
— Eleven strains of microorganisms were examined for their susceptibility to death by irradiation with 21–30 mW of light at 6328 Å from a continuous‐wave gas laser. Washed cells of seven species were rapidly killed when irradiated aerobically in aqueous solutions of toluidine blue: Sarcina lutea (two strains), Escherichia coli, Chromobacterium violaceum, Arthrobacter atrocyanus, Pseudomonas aeruginosa, Saccharomyces cerevisiae , and Rhodotorula glutinis. Cells remained viable when irradiated anaerobically in toluidine blue. This is not proof that oxygen is required for death since toluidine blue is subject to reduction to the leuco form under anaerobic conditions. None of the microbes tested, including cells of Bacillus cereus, Rhodospirillum rubrum , and Euglena gracilis , were killed in aerated suspensions without toluidine blue. Thus, it is unlikely that any strain has an endogenous photosensitizer capable of acting at 6328 Å. However, more than 95 per cent of the cells of R. rubrum lost their motility. A colorless mutant of S. lutea began dying 10 min faster than the wild strain, which is known to be protected from photosensitized death by carotenoids for at least 2 hr when irradiated in toluidine blue with 1000 ft candles of tungsten light. Since toluidine blue is bleached in irradiated cell suspensions, logarithmic death ceases within an hour with 2·5 × 10 =6 M toluidine blue. Yeasts are less susceptible than bacteria, exhibiting longer lags before death begins. The size of colonies produced by irradiated yeast cells decreases with irradiation time. This suggests that multiple hits are required for death.