Membrane damage and recovery associated with growth delay induced by near-UV radiation in Escherichia coli K-12

Abstract

The growth delay induced by near-UV radiation has been largely attributed to injured tRNA's and to the stringent response. We report an associated membrane perturbation whose recovery determines substantial modifications in the behavior of log phase Escherichia coliK–12 exposed to sublethal doses of near-UV radiation (366 nm). When incubated at 37°C in plain nutrient broth, cells suffered a growth delay of about 100 min with parallel inhibition of several membrane functions. Conversely, when grown in conditions known to influence membrane activities, these were slightly inhibited and the growth delay lasted about 50 min. All the above conditions triggered the stringent response, characterized by an equivalent post-irradiation burst of intracellular guanosine 5′3′ tetra and pentaphosphate and by a similar decay rate of the nucleotides accumulated at time 0 of the growth lag. According to our data the polyphosphates' half decay time in irradiated cells remains practically constant and close to 15 min. But, while cells from unsupplemented broth at 37°C resumed normal growth in around 100 min those with recovered membranes were rescued from growth inhibition in about one half of that time.