ADAPTATION 16-5 



When glucose is added to a medium containing lactate (which 

 without glucose would support immediate growth) there is a very 

 long period between inoculation and the appearance of measurable 

 growth followed suddenly by a period of very rapid growth. On the 

 average 150 to 170 hours were required on mixtures of lactate and 

 glucose; one culture adapted after only 40 hours but several failed 

 to grow appreciably until after 10 or more days. 



In the absence of lactate No. 97 requires an incubation period 

 of nearly 200 hours before it begins to grow on 4 per cent glucose. 

 However, after that incubation period the growth is extremely rapid, 

 indicating that adaptation is complete. On 1 per cent glucose a 

 longer adaptation period is required and the adapted cultures do 

 not grow nearly so rapidly. By comparison No. 322 requires no 

 adaptation and growth progresses at a maximum rate. 



Fig. 16-3 shows that when half per cent lactate is added to 4 per 

 cent glucose No. 97 begins to grow much sooner, but the growth rate 

 is not so great as in the absence of lactate, and after an initial rapid 

 increase there is a period of lag and a second period of increasing 

 growth rate. One per cent glucose with half per cent lactate shows 

 a greater variation in the secondary phase of growth, and a corres- 

 pondingly longer delay before growth begins. A comparison of figs. 

 16-2 and 16-3 reveals that adaptation to glucose is complete in the 

 absence of lactate after a relatively long lag period, and that higher 

 concentrations of glucose produce more effective adaptation than low 

 concentrations. When lactate is added to glucose the nonutilizer of 

 glucose begins to grow a little sooner but the growth rate is less 

 rapid, indicating that adaptation to glucose is not complete and that 

 the presence of lactate inhibits this adaptation. A secondary phase 

 in growth indicates that subsequent steps occur in adaptation to glu- 

 cose. It is also clear that the presence of glucose interferes with 

 utilization of lactate because on lactate culture No. 97 begins to grow 

 immediately without any lag, and 120 hours are required before 

 growth begins on the mixture. 



Figs. 16-4 and 16-5 in which increasing concentrations of lac- 

 tate are used, confirm the above conclusions and show in addition 

 that the growth of the glucose utilizer is inhibited on high concen- 

 trations of lactate, although 0.5 per cent has no harmful effect, sug- 

 gesting that harmful effects of lactate do not account for the irregu- 

 larities of growth on No. 97 shown in fig. 16-3. The starting time 

 of rapid growth varies greatly from one culture to the next. Some 

 data for individual cultures are presented in Table 16-1. The adapta- 

 tion times, the points of intersection of the abscissa with the slopes 

 of the growth curves in the regions of rapid linear growth, repre- 

 sentapproximatelythe periods required for adaptation to glucose 

 utilization. In most cases they correspond to the times of appear- 

 ance of sufficient yields to be measurable in the Klett photometer. 



