Neighbour restoration: a possible explanation for some "broken" survival curves of UV-irradiated Escherichia coli K12 cells.
Survival curves for UV irradiation of five non-filamenting strains of E. coli K12 decrease exponentially at moderate levels of radiation but are broken at high levels of radiation. That is, it appears a change in the slope of survival curves, featuring a tail. As this phenomenon was observed with strains bearing uvrA and recA mutations it must be independent of the products of these genes. Experiments with isolated surviving colonies and synchronized cultures eliminated genetic and phenotypic heterogeneity as reasons for the tails in the survival curves. UV survival increased 10- to 15-fold when UV-irradiated cells were plated either with cells unable to grow in the plating medium or with bacterial cell-free extracts. We suggest that factors related to the high cell densities used to obtain survival curves at high radiation levels (neighbour restoration) could be responsible for the survival increases, generating the tailed survival curves.
Bernardo-Filho
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M
Instituto de Biologia, Universidade do Estado do Rio de Janeiro, Brasil.
Leitao
A C
AC
Alcantara-Gomes
R
R
D004926:Escherichia coli / Q000145:classification / Q000254:growth & development* / Q000528:radiation effects; D014466:Ultraviolet Rays