6 HAROLD R. CURRAN 



Schrieber, 0. 1896. Ueber die physiologischen Bedingungen der endogenen 



Sporenbildung bei Bacillus anthracis, subtilis und tumescens. Zentr. 



Bakt. Parasitenk. Abt. I. Orig. 85: 1-12; 20: 35-374. 

 Tarr, H. L. A. 1932. The relation of the composition of the culture medium 



to the formation of endospores by aerobic bacilli. J. Hygiene 32: 535- 



543. 

 Ward, B. Q. 1947. Studies on the Sporulation of Bacillus thermoacidurans. 



Thesis, University of Texas, p.1-90. 

 Weinberg, E. D. 1955. The effect of Mn++ and antimicrobial drugs on 



sporulation of Bacillus subtilis in nutrient broth. J. Bact. 70: 289-296. 



Discussion 



E. D. Weinberg 



Dr. Curran has given us an excellent review of the literature in this area 

 of spore research and his paper should be of great value to future investi- 

 gators in this field. 



In any study of mineral nutrition, the usual obstacle is the presence of un- 

 suspected or undetectable trace amounts of metallic ions in the environment. 

 Even in our present-day synthetic media there may exist unknown metal 

 contaminants that are required in higher concentrations for sporulation than 

 for vegetative growth. Or perhaps there exist in some media in use today 

 trace metals that inhibit sporulation. To illustrate such a possibility we can 

 recall the extreme variations in amount of diphtheria toxin obtained in dif- 

 ferent culture media before 1936. At that time it was finally realized that 

 although one part of iron in ten million parts of medium is required for 

 maximum toxin production, as little as five times that quantity of iron per- 

 mits perfectly good cellular multiplication of diphtheria bacilli but com- 

 pletely suppresses toxin production. 



Fortunately, however, the development of methods for the preparation of 

 synthetic demetalled media and for the detection of trace metal contam- 

 inants has progressed greatly during the past decade. And recently the 

 Society of General Microbiology has made a start towards our understand- 

 ing of the mineral composition of complex media of plant and animal orgin. 



Oddly enough, the chief difficulty in mineral nutrition that confronted 

 workers in sporulation for a half-century was not the presence of an unde- 

 tected metallic ion in their media but rather the opposite situation: that is, 

 the lack of sufficient potassium and manganese, and sometimes magnesium, 

 in complex media derived from animal products. How could anyone have 

 predicted that peptone and meat extract and skim milk contain sufficient 

 available manganese for the growth of most microbial cells including those 

 of the genus Bacillus but contain insufficient available manganese to enable 

 cells of aerobic bacilli to efficiently sporulate? And think for a moment of 



