Reactivation of Cells Inactivated by UV light and Other Stress Factors

5 Reactivation of Cells Inactivated by UV light and Other Stress Factors 

Among the species of propionibacteria tested, i.e., P. rubrum, P. raffinosaceum, P. acidipropionici, P. shermanii, P. coccoides, P. acnes the highest effect was found in P. shermanii and P. acidipropionici, while P. coccoides and P. acnes did not exert any protective effects in UV-inactivated E. coli cells (Vorobjeva et al., 1996b). The protective substances in the extract are dialyzable and have molecular weights higher than 12 kDa. 

A similar protective action was foxmd both in the case of pre- (5 min) and postincubation (30 min) of the extract with irradiated cells. Thus a screening action of the extract can be largely excluded by these observations. Heating the dialysate for 10 min at SOX and 70 0 or for 1 min at 92°C caused some reduction of its activity, which still remained relatively high, but upon heating for 12 min at 92 C the activity was reduced three-fold. Reactivative activity of the extract was retained after storage up to 1.5 months at -20 C and more than one year after lyophilization. Lipase treatment had no effect on the reactivative activity of the extract RNAse and especially DNAse treatment lowered it significantly, while proteinase K treatment alone or followed by trypsin treatment reduced the activity 5.5-fold or completely, respectively. 

Previously (Adler et al., 1966), only filamentous strains of E. coli have been shown to be reactivated by an extract of E, coli, and reactivation was related to the mechanism of the initiation of cell division. We have for the first time demonstrated reactivation of a nonfilamentous strain of E. coli AB1157 by extracts of propionic acid bacteria. Possible mechanisms of reactivation include stimulation of reparation systems, antimutagenic action and/or stabilization of DNA. The protective effect was very high, reaching a factor of 25 (calculated as the ratio of the number of colonies grown in the presence of extract, to the number of colonies grown in the absence of extract), although the complete recovery of all the cells was never reached. This phenomenon may perhaps be explained by the fact that the maximal effect was observed at a very low viability of the injured cells (0.006%). 

To investigate the protective mechanism of the dialysate, the latter was tested on isogenic E. coli strains with various impairments of the DNA repair systems. The sensivity to UV light increased in the following order E coli ABl 157, PolA, UvrA, and RecA. In the mutant PolA-1 the systems for rapid DNA repair and excision repair by short fragments are blocked due to the lack of DNA polymerase 1. The mutant has the system of excision repair. 

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