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CULTURE MEDIA. J. W. WOODROW, A. C. BAILEY ANID E. I. FULMER .... The effect of ultra-violet light upon the carbohydrates in solution has been studied by ...
THE EFFECT OF ULTRAVIOLET RADIATION UPON YEAST CULTURE MEDIA J. W. WOODROW, A. C. BAILEY ANID E. I. FULMER

(WITH ONE FIGURE)

While a great deal of work has been done on the effect of ultraviolet radiation upon the growth of yeast and other microorganisms, the effect of the rays upon the culture medium itself, so far as its growth-promoting properties are concerned, has not been adequately studied. It is obvious that the effect of the ultraviolet rays upon the organism in the medium may be due to a combination of factors, the direct effect upon the organism and an indirect action due to changes in the composition of the medium. This communication presents data on the effect of ultraviolet radiations upon the ability of several culture media to support the growth of yeast. Equipment and methods The source of the rays was a Cooper-Hewitt quartz lamp operated on a direct current of 110 volts and 4 amperes. WTratten filters were used in some cases to control the range of radiations used, and clear quartz "Vitreosil" Erlenmeyer flasks and Pyrex flasks were used as culture vessels. The culture of Saccharonyces cerevisiae had been growing continuously for a period of years upon synthetic media. The counts were made with the Jhoma-Zeiss chamber. When the count is one there are 250,000 cells per cubic centimeter. All incubations were made at 300 C. The intensity of the ultraviolet was measured in lithopone units according to CLARK (16). This unit is defined as the energy required to darken the lithopone paste to a reflection factor of 50. Exposures of the media were made at 16 cm., under which condition six seconds were required to produce the standard darkening. The media used were C, D and E as developed and described by FULMER, NELSON and SHERWOOD (18). The composition of these media, in terms of grams of solute per 100 cubic centimeters of medium, is shown in table I. Each flask was weighed with contents before inoculation so that any evaporation during sterilization or irradiation could be compensated by the addition of the required amount of sterile water. In each instance 25 cc. of the medium were used in a 50 cc. quartz or Pyrex flask. The flasks were tipped at an angle so as to receive a maximum amount of the radiant energy. 171

172

PLANT PHYSIOLOGY

TABLE I COMPOSITION OF

YEAST MEDIA USED

MEDIUM

CONSTITUENTS

C

NH4C1

.................................................

EHPO 2

CaCL2 CawOO

4

........................

g. 0.188 0.100

Sucrose ...

.............................

D

E

gnm.

gm. 0.188 0.100 0.100

0.188 0.100 0.100

. ..

....

_

_

............

............

0.040

10.000

10.000

10.000

Experimental results The results obtained for medium E irradiated for various time intervals are shown in figure 1. For comparative purposes the growth in the nonirradiated control flask has been taken as one hundred. These results show that with both the quartz and Pyrex flasks irradiation causes the development of toxicity in the medium, the effect being much greater for the quartz. These results are typical of many experiments. Irradiation of media C and D gave the same general results both for quartz and Pyrex flasks as those for medium E. Evidently the presence of the calcium chloride or carbonate does not influence results.

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