Studies on the Growth of Bacillus Megatherium de Bary

1) A survey of the literature concerning the morphological and physiological properties of bacterial growth in strong salt solutions is given. 2) A review of the literature on variability of bacteria revealed the fact that, although various authors advocate a modifying action of the milieu on the potentialities of the bacterial species, others explain the same phenomena without such an assumption. 3) A theory was developed in which all variation-phenomena were classified into three groups: fluctuating variability, dissociative variability, and “jumping” variability. A new terminology was proposed, dropping all genetical concepts. 4) Quantitative experiments on growth of B. megatherium in NaCl-peptone-solutions confirmed the data given in the literature on this subject. The growth-velocity decreased with increasing salt-percentage, the incubation-time was prolonged, a larger inoculum was indispensable in higher percentages. 5) During growth in NaCl solutions there proved to be a period, directly after inoculation, where retransfer to salt-free peptonewater yielded no growth. 6) With the plate count method growth-curves were constructed for growth in various percentages of salt. 7) The curves show a decrease in the first hours, while the first point showed that only a fraction of the inoculum was able to develop. 8) The initial decrease was explained as the resultant of two relations; the growth curve of those cells that did develop, and the death-curve of those that autolyzed. 9) It was possible to separate the components. The curves obtained in this way, recalculated to comparable growth-velocity, fit very well into a bundle of curves for growth in salt-free milieu. 10) The autolysis of a fraction of the inoculum could be demonstrated by nephelometric methods. xi) With extremely small inocula no growth at all was observed in percentages over 6 %, and the curves obtained this way gave an expression of the autolysis. 12) All cultures grew in all percentages in tortuous filaments; the so called “clusters”. On retransfer to saltless media, the original morphology was restored. The amount of cells per “cluster” was low in the beginning and in the end, but maximal in the time that growth had its maximum. 13) Cultures growing in salt-solutions had the property to form nearly as many colonies on salt-plates as on salt-free agar. Cultures growing in salt-free peptone-water did not show this property. These cultures showed a maximum susceptability against salt during the “lag-phase”. 14) Because the property to form nearly 100 % colonies on saltplates was directly and completely lost on retransfer to saltless media, and also because of their altered morphology, the colonies were looked upon as results of the modifying action of the milieu on the limits of fluctuating variability. This investigations were carried out in the Botanical Laboratory of the University of Leyden. I am very much indebted to its Director, Prof. Dr. L. G. M. Baas B e c k i n g, for his suggestions and valuable help for which I wish to thank him particularly. Furthermore I wish to thank the technical staff of the Laboratory for constant help, especially Mr. J. E. Bevelander who carefully prepared the figures.