10 



A. L. PlERRTORFF 



ETIOLOGY 

 CULTURAL REACTIONS OP BACILLUS AMYLOVORUS 



The complete cultural reactions of Bacillus amylovorus were not rede- 

 termined by the writer, since these have been described by Jones 

 and Morse (1903), 1). II. Jones (1909), Stewart (1913), and 

 Smith (1920). These workers have reported the acid tolerance in terms 

 of Puller's scale, since the hydrogen-ion concentration is now used by 

 most bacteriologists to express acidity of culture media, the writer has 

 adopted that method, using the quinhydrone cell for making pH 

 determinations. 



In order to be certain that growth of the bacteria would not be 

 inhibited in some of the acid cultures to be used in testing for enzymes, 

 Stewart's (1913) work on acid tolerance was repeated, lie gives the 

 limit of acid tolerance of B. amylovorus as 23 to 25 Fuller's scale. 

 This would be approximately pll 5.90 to .1.70. 



Growth in nutrient bouillon, made with prepared beef extract acidified 

 with malic acid, was obtained by the writer as low as pll 4.60. or 36 

 Fuller's scale. The comparative rate of growth of the bacteria is 

 indicated by the number of colonies in the dilution plates in which a 

 standard volume of culture was diluted (table 2). 



TABLE 2. Acid Tolerance of Bacillus amylovorus in Nutrient Bouillon 



* Checks all sterile. 



The tests were made in quadruplicate. At the time when the plates 

 were poured, four agar slants were inoculated from tin 1 bouillon cul- 

 tures with pH of 4.60 and below. After eight days several colonies 

 appeared on the slants inoculated from bouillon at pH 4.60, 4.44, 

 and 4.38, but none from pH 4.02 or below. No growth in the bouillon 

 tubes could be detected with the eye at this range. It is possible 

 that little or no growth took place in these tubes, but that the bacteria 

 originally introduced remained viable. \t appears from these tests 

 that />'. amylovorus is able to grow in a more acid medium than was 

 formerly supposed. 



