MUTAGENESIS 115 



manganese chloride. This, I think, is the most curious mutagen of all. 

 So far, it has produced mutations only in bacteria and only in certain 

 strains of bacteria, although it has been tested on other microorganisms. 

 Did it act on Salmonella, Dr. Demerec? 



Denierec: Yes, it does. 



Auerbach: But much more on E. colli 



Demerec: Yes. 



Auerbach: And even in E. coli, more on certain strains than on 

 others. In Penicillium, it does the opposite. It is an antimutagen to 

 nitrogen mustard. I think, in this case, the explanation which Dr. 

 Demerec gave long ago is correct — that it acts in some rather un- 

 specific ways by disturbing the metabolism of the bacterium and prob- 

 ably upsetting defense mechanisms wliich preserve the integrity of 

 gene reproduction. 



Neel: I wonder if Dr. Demerec would summarize the work with 

 manganese chloride now? 



Auerbach: May I say something? Dr. Demerec told me a very 

 interesting story about aminopurine yesterday. I was just wondering 

 whether he could repeat this now. 



Demerec: The work with manganous chloride was published in an 

 extensive paper in 1951 (15). It was done in the early days of our 

 research with bacteria, when we were developing techniques for study- 

 ing induced mutagenesis in Escherichia coli and had begun testing 

 chemicals to see which ones were mutagenic. In our survey, which was 

 done with Joe Bertani (14) , we included 31 chemicals representing 

 some widely separated groups. Nineteen WTre found to be mutagens. 

 Among these was manganous chloride, with which studies were con- 

 tinued because it showed several unusual properties. In the first place, 

 it was a very potent mutagen, inducing mutations under conditions of 

 treatment that produced very little or no killing. Moreover, its muta- 

 genicity could be modified by certain pretreatment and posttreatment 

 of the bacteria. We found that the mutagenic effect increased linearly 

 with concentration, up to 2.5 X lO'^M, and with time treatment up to 

 30 minutes, after which further increases in either concentration or 

 time were ineffective. Washing of the bacteria before treatment, in 

 water or in hypotonic solutions of NaCl, KCl, CaClo, sucrose or 

 dextrose decreased the frequency of induced mutation, whereas wash- 

 ing in hypertonic solutions of these compounds increased it. Washing 

 in similar concentrations of various other salts resulted in lower muta- 

 tion frequencies than washing in NaCl or KCl, in the following 

 descending order: CaClo, BeFL, UO.Clo, CdCL, CrClg, C0CI2, 



