26 
Exercise 13. The Production of Pigment by Bacteria 
MATERIALS: 
6 plain agar slants 
6 glucose agar slants 
3 plain gelatin for stab cultures 
3 glucose gelatin for stab cultures 
One culture each of Ps. prodigiosus, Ps. flurorescens and Aero- 
bacter aerogenes. 
1. Prepare one plain gelatin and one glucose gelatin stab culture from each 
of the cultures as follows: Make sure the transfer needle is straight. Sterilize 
the needle, cool, and touch the tip to the bacterial growth. Carefully make a 
stab with the inoculated needle in the center of the gelatin. The stab should 
be made parallel to the sides of the tube, and within a few millimeters of the 
bottom. 
2. Place the three cultures, labeled and held together by means of a rubber 
band, in ice-water until they can be placed in the 20°C incubator. 
3. Prepare two plain and two glucose agar slant cultures of each of the 
organisms. 
4. Place one plain agar slant and one glucose agar slant of each culture at 
room temperature. Incubate the other plain and glucose agar slants at 37°C. 
5. Examine the cultures every 48 hours for one week. 
6. At the end of a week record, in table form, the absence of pigment as — 
and different degrees of pigment as +, + -f, or + + +. Brightness of pigment 
should be considered and not the amount of growth. 
7. Place a few cc. of each of distilled water, chloroform, and carbon 
bisulphide in small test tubes. Add a large loopfull of the brightest pigmented 
culture to each. Observe any solubility in the solution. 
8. (a) Where in the cultures is the pigment seen most conspicuously? 
( b ) How may this be explained? 
(c) What composition of the medium is the most favorable for 
pigment production? 
(d) What temperature is most favorable for pigment production? 
(e) What does this suggest about the habitats of the organisms? 
(0 What is the relation of oxygen to pigment production? 
(g) What cultures showed this? 
{h) What pigments are water soluble? 
(i) What are pigment-producing organisms called? 
(J) What is the practical agricultural significance of pigment- 
producing organisms? 
