260 Discussion 



Salmonella it has been observed in my laboratory that on being put back 

 into broth at 37°, after having been kept at 4° for many hours, Salmonella 

 cells may for several generations grow in chains, like a rough organism, 

 although on subculture they return to their original form, growing in 

 short rods (Rogers, H. J. (1957), J. gen. Microbiol., 16, 22). It has been 

 shown that staphylococci, taken from a fully grown broth culture and 

 allowed to come back into exponential growth in broth, began to syn- 

 thesize hyaluronidase ; but it took about eleven generations of exponen- 

 tial growth before they reached a steady-state of enzyme secretion per 

 cell per generation. Something similar might be involved here perhaps. 



Alexander: There is some very good evidence from radiation experi- 

 ments which supports Prof. Kunicki-Goldfinger's view that on cooling 

 cells the various physiological processes are not all slowed down to the 

 same extent, so that by keeping them cold one can get a change in the 

 biochemical make-up of the cell. This was first shown by Hollaender, 

 who found that on irradiation of a cell two competitive processes occur, 

 both of which are physiological : the development of the injury and the 

 repair processes. Hollaender found that by storing cells, after irradiation, 

 at a low temperature he was able to increase greatly the number of 

 survivors, because these two competitive processes were not affected to 

 the same extent by temperature. This is known for many other systems. 

 I wonder whether keeping them as low as 4° might not be too low, 

 because in his experiments Hollaender got the best recoveries when he 

 kept them between 12° and 18°. 



Kunicki-Goldfinger : At 10° we got rather similar results, but the 

 increase was smaller. 



Lederberg: Contrary to the expectations that have been expressed, 

 the shift from the cold-induced state to the normal appeared not to 

 occur during exponential growth, but only during the saturation stage 

 of the culture. Has that been systematically investigated, using different 

 periods of exponential growth, to see whether the shift back to sensitivity 

 occurred at different intervals, depending on the duration of the log 

 phase ? 



Kunicki-Goldfinger: This has not been done. 



Lederberg: I would suggest that you have here a persistent effect of 

 Dauermodifikation, which is so far w^ithout clear precedent for bacteria, 

 certainly not for Esch. coli K 12. It might be feasible to use a form of 

 genetic analysis for the investigation of the difference between them. 



Kunicki-Goldfinger : We are preparing such an experiment now. 



Davis: Do you know whether keeping cells for a relatively long period 

 in the stationary phase will have much effect on phenotypic strepto- 

 mycin resistance? 



Kunicki-Goldfinger: No; the duration of experiments was only 72 

 hours. 



Knox: Does freeze-drying have any effect? 



Kunicki-Goldfinger: I have not tried that. 



Gyorffy: We have carried out similar experiments with non-dividing 

 Serratia marcescens cells. We used 20-hour cultures, washed repeatedly in 

 phosphate buffer and then incubated in rolled tubes overnight, and then 



