Abstract
is the etiological agent of plant tumors, known as crown-gall disease. 1 The importance of investigating the chemical composition of this organism and the pathological effects of its various constituents is apparent. Although the etiology of plant tumors probably does not parallel that of animal cancer, the fact that a chemical stimulant of cellular proliferation apparently is synthesized by this microörganism is reminiscent of certain results obtained with chemically well-defined carcinogenic agents. Doubtless, a deeper knowledge of the mechanism underlying the development of plant cancer would also be of value for a better understanding of malignant growth in general.
A virulent strain of B. tumefaciens (strain 6NIS6) was cultivated on sterile bean-broth in the dark at room temperature for 14 days. The washed bacteria were suspended in a mixture of equal amounts of alcohol-ether which extracted the fat and phosphatide. The defatted organisms then were extracted with chloroform, in order to remove the wax fraction which, however, in this bacterium is very small and was not further examined. The separation and purification of the lipids were carried out according to the method of Anderson. 2 The distribution of lipids in 3 batches of bacteria of the same strain grown at different times is given in Table I. It will be seen that the results are remarkably uniform. The dry weight of the bacteria examined, in each case, was between 2 and 3 gm.
The acetone-soluble fat is a yellow viscous oil. Its constants, determined according to the micro-method described by one of us 3 were: iodine No. 95.0, saponification No. 201.2, acid No. 53.2, ester No. 148.0. On saponification (carried out in N2) the following components were obtained from 174 mg. of fat: 15.6 mg. of unsaponifiable matter (9% of the fat) and 142.9 mg. of fatty acids (82.1% of the fat). The unsaponifiable fraction showed no selective absorption in the ultraviolet region in alcohol-chloroform (2:1) solution; there was only an end-absorption around 2350 Å. About 10% of the unsaponifiable fraction consisted of a sterol mixture which melted unsharply around 80°, was precipitated by digitonin and gave a positive Liebermann-Burchard reaction and a negative Rosenheim reaction. This sterol may have been carried over from the medium. The fatty acids (142.9 mg.) were separated into the solid and liquid acids according to the Twitchell procedure. The solid acids weighed 30.0 mg. and had the iodine value 43.3; the liquid acids weighed 106.4 mg. and had the iodine value of 51.6. The fat apparently contains unsaturated fatty acids of high molecular weight, as is also the case with the fat of C. diphtheriœ. 4
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