Rare UV-resistant cells in clonal populations of Escherichia coli.

Shunsuke Ichikawa, Mika Okazaki, Mina Okamura, Norihiro Nishimura, Hideto Miyake

Journal of photochemistry and photobiology. B, Biology 2022 Jun

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Water disinfection is one of the most important applications of ultraviolet light-emitting diodes (UV-LEDs), though bacterial regrowth remains a serious problem. In this study, we showed that UV-resistant cells, though rare, exist in an Escherichia coli clonal population. The UV-resistance of stationary phase cells was higher than that of exponential phase cells. Regrowth cell populations showed identical UV sensitivity before and after UV treatment, indicating that UV resistance is not acquired genetically, but is generated stochastically. The characteristics of these UV-resistant cells are similar to those of non-heritable antibiotic-resistant cells, termed persisters. The induction of persister formation increased the number of viable cells after UV treatment. The toxin-antitoxin system gene hipA (high persistence A) is a key factor in persister cell formation. We observed that hipA was strongly expressed in the stationary phase cells, while regrowth cells after UV treatment lost hipA expression, suggesting that the regrowth cells lost their persistence. Compared to UV batch radiation, we demonstrated that intermittent UV irradiation, which included the induction of regrowth between UV treatments, significantly reduced the number of viable E. coli cells. Copyright © 2022 Elsevier B.V. All rights reserved.

Citation

Shunsuke Ichikawa, Mika Okazaki, Mina Okamura, Norihiro Nishimura, Hideto Miyake. Rare UV-resistant cells in clonal populations of Escherichia coli. Journal of photochemistry and photobiology. B, Biology. 2022 Jun;231:112448