Apkil 23, 1915] 



SCIENCE 



621 



The determination of the various physical and 

 physico-chemical forces will serve to give some 

 idea of the factors which microorganisms have to 

 overcome in growing in gelatin and similar media 

 of high concentration. 



This experiment was worked out by Mr. 0. M. 

 Gruzit, a senior student. 



Induced Variations in Chromogenesis: M. E. 



Smibnow. 



Of the various biological characters of bacteria, 

 one of the most interesting yet least important is 

 that of pigment production. Though considerable 

 efforts have been expended in the study of this 

 function, little of real value is as yet available. 

 It appears that this property is especially promi- 

 nent amongst the saprophitic organisms, and de- 

 pends to a greater or less extent, on certain con- 

 ditions of environment which vary with different 

 bacteria, and is, as a rule, more or less constant for 

 the same organisms. 



With the exception of Spirillum rubrvm and 

 possibly a few others, the chromogenic bacteria re- 

 quire an abundance of free oxygen, giving no pig- 

 ment under anaerobic conditions of growth. Tem- 

 perature also seems to determine pigment pro- 

 duction of some bacteria, thus the B. prodigioms 

 will give no pigment at 37° C. 



Perhaps the most important influencing agent 

 on the function of chromogenesis is the medium 

 on which the organism is grown. With other fac- 

 tors of environment constant, chromogenesis will 

 vary with the medium employed. Gessard, for 

 instance, has shown that the B. pyoeyaneus will 

 produce only a blue color, of a most beautiful 

 shade, in a two-per-cent. solution of peptone, 

 which may be increased in intensity by the addi- 

 tion of five-per-eent. of glycerin. When grown on 

 egg-white or other albumen or on weak glucose 

 media it would produce a fluorescent green. This 

 same organism when grown on a five- or six-per- 

 cent, glucose medium or on immune serum would 

 give no pigment. He believes that phosphates 

 are required for the production of the fluorescin. 

 Substances that enhance the value of culture 

 media, in a general way increase also the pigment 

 proauction. Other substances, as acids or alka- 

 lies, may diminish or even inhibit its production. 

 Some organisms may give different colors on 

 media of different reaction. Thus the B. prodigi- 

 osus gives a distinct yellow color on alkaline, and 

 a violet-red on acid media. 



In what manner the pigment is produced is not 

 yet known. It is regarded that the property of 

 pigment production keeps pace with other biolog- 



ical characters, as enzyme formation. This, the 

 writer does not feel to be correct, inasmuch, as 

 will later be shown, he has succeeded in increas- 

 ing the chromogenic properties of some bacteria 

 with a coincident decrease of enzyme formation. 

 Some of the higher forms of organisms give rise 

 to pigment as a function closely related with their 

 nutrition and may possibly be regarded as prod- 

 ucts of metabolism. In these oases the pigment 

 is obtained from the medium and is stored up in 

 the bodies of the cells, as in the case of sulphur 

 bacteria. Or, it may be produced on certain 

 media containing iron, as evidenced in the so- 

 called iron bacteria, through the products of 

 metabolism and the production of sulphide or 

 iron. 



Chromogenesis may be increased not only by 

 growing the bacteria on more favorable media 

 and environment, but also by the process of selec- 

 tion, transplanting each time from portions of the 

 culture or from a colony that shows the most pro- 

 nounced pigment. 



Experimentally induced variations in the chro- 

 mogenic properties of the StapTiyloooccus pyo- 

 genes aureus may be brought about by exposure 

 to phenol or by growth in phenol, glucose, sodium 

 sulphate or sodium chloride broth. Nine different 

 strains of the Staphylococcus were used in the 

 work here reported. Five of these were old stock 

 cultures giving little or no color; the remainder 

 were a few months old and showed a fair amount 

 of pigment at the beginning of the experiments. 

 The organisms were grovm in the above media 

 for from six to ten weeks, being transplanted 

 every three or four days during the entire time. 

 They were then grown on potato and blood serum 

 media for from 24 to 120 hours, and the effect on 

 chromogenesis noted. 



The increase of chromogenesis is brought about 

 more readily by growing the organisms in phenol 

 broth than by exposing them to 75 per cent, 

 phenol solution and transferring on to agar. Of 

 the nine strains used phenol markedly increased 

 the chromogenic properties in six, Nos. 1, 2, 5, 

 6, 7, 8; slightly increased it in Nos. 4 and 9 and 

 left No. 3 practically unchanged or even slightly 

 diminished. Growth in dextrose, sodium chloride 

 and sodium sulphate broth invariably decreased 

 or left unchanged the quantity of pigment pro- 

 duced. Often almost a pure white growth of the 

 various cocci, subjected to the growth in NaCl 

 and Na-SOj broth, would be seen when transferred 

 to potato or blood serum. 



An old stock culture of the B. prodigiosus was 

 also used. This organism gave the slightest trace 



