136 Discussion 



DISCUSSION 



Harington: Prof. lerusalimsky, I believe you have some data which 

 you would like to report now. 



lerusalimsky : The experimenters working on adaptation of micro- 

 organisms did their best to distinguish physiological non-hereditary 

 changes from spontaneous mutations. Nature, however, does not know 

 any hard and fast rules. It is possible to admit the existence of cate- 

 gories intermediate between non -hereditary modifications and hereditary 

 changes. It is common knowledge that the precious qualities developed 

 in cultivated plants are inherited by them during an unlimited length 

 of time in vegetative reproduction. However, some of these qualities 

 can very easily disappear in the case of reproduction by means of seeds. 



Bacteria undergo adaptive changes which could be transferred to one 

 or to many generations of vegetative cells. However, it seems to me 

 that only those changes that are transferred through sexual or asexual 

 reproductive cells could be considered truly hereditary. To my mind, 

 a certain kind of analogy of the latter are spores. The life cycle of 

 bacteria ends in spore formation; and ince versa, germination of spores 

 starts the next life cycle. During the formation of the spore, essential 

 changes occur in the cellular structure and the greater part of the cellular 

 content is not included in the spore. One should assume that it is the 

 most stable properties, which can be considered hereditary, that will be 

 transferred through spores. Unstable changes, which are retained in 

 vegetative reproduction alone and disappear in spore formation, should 

 be considered non-hereditary. To quote an example: strain CL aceto- 

 hutylicimi, which we had at our disposal, ferments xylose after a certain 

 period of adaptation. Proof of this can be obtained by seeding the spores 

 into glucose and xylose media (Fig. 1). The cells, once they start to 

 produce enzymes, continue to propagate and they ferment xylose at 

 almost the same rate as glucose. 



However, the above is true only in those cases where the cells seeded 

 are vegetative ones. As soon as the cells in the xylose medium form 

 spores, their newly acquired capacity disappears, and again a certain 

 amount of time will be needed to produce adaptive enzymes (Fig. 1). 

 Consequently, the ability to produce these enzymes at an increased rate 

 is not transferred through spores and therefore cannot be considered 

 hereditary. 



Could the changes which were induced by environmental factors be 

 so strengthened and stabilized as to be transferred through spores, and 

 thus become hereditary? 



I shall mention only one example confirming the possibility of the last 

 statement. We adapted CI. aceto-butylicum to increased concentrations 

 of butanol. The bacteria were cultivated in an apparatus for continuous 

 cultivation, the concentrations of butanol increasing gradually (by • 2- 

 0-5 per cent at a time). After each increase of concentration the rate 

 of bacterial propagation dropped considerably; and only after a long 

 period could the rate be increased again to that of propagation of the 

 control culture, after which time we increased the concentration of 



