Interspecies variation in survival and growth of filamentous heterotrophic bacteria in response to UVC radiation

Ultraviolet radiation is an important environmental constraint on the evolution of life. In addition to its harmful effects, ultraviolet radiation plays an important role in generating genetic polymorphisms and acting as a selective agent. Understanding how prokaryotes cope with high radiation can give insights on the evolution of life on Earth. Four representative filamentous bacteria from the family Cytophagaceae with different pigmentation were selected and exposed to different doses of UVC radiation (15-32,400Jm(-2)). The effect of UVC radiation on bacterial survival, growth and morphology were investigated. Results showed high survival in response to UVC for Rudanella lutea and Fibrisoma limi, whereas low survival was observed for Fibrella aestuarina and Spirosoma linguale. S. linguale showed slow growth recovery after ultraviolet exposure, R. lutea and F. limi showed intermediate growth recovery, while F. aestuarina had the fastest recovery among the four tested bacteria. In terms of survival, S. linguale was the most sensitive bacterium whereas R. lutea and F. limi were better at coping with UVC stress. The latter two resumed growth even after 2h exposure (～10,800Jm(-2)). Additionally, the ability to form multicellular filaments after exposure was tested using two bacteria: one representative of the high (R. lutea) and one of the low (F. aestuarina) survival rates. The ability to elongate filaments due to cell division was preserved but modified. In R. lutea 10min exposure reduced the average filament length. The opposite was observed in F. aestuarina, where the 5 and 10min exposures increased the average filament length. R. lutea and F. limi are potential candidates for further research into survival and resistance to ultraviolet radiation stress.