II44-14 MANUAL OF METHODS FOR PURE CULTURE STUDY 

 3. SYNTHETIC MEDIA 



Ashby^s mannitol solution. In one litre of distilled water dissolve 

 the following: 



Mannitol 20.0 g. NaCl 0.2 g. 



K.HPO4 0.2 g. CaS04+2H,0 0.1 g. 



MgS04+7H,0 0.2 g. CaCOi 5.0 g. 



Method of sterilization not specified by author; autoclaving presumably satisfactory. 

 Use: Cultivation of Azotobacter. 



Synthetic carbohydrate media. Peptone-free media are often valu- 

 able in measuring increases in hydrogen-ion concentration when only 

 small quantities of acid are produced. A formula slightly modified 

 from one proposed by Ayers, Rupp and Johnson (1919) is as follows: 



NH4HaP04 1.0 g. 



KCl 0.2 g. 



MgS04+7H.O 0.2 g. 



Water 1000 ml 



Sugar (or other carbon source) .... 10 g. 



This may be employed as a liquid medium without or with the addi- 

 tion of indicator; or as a solid medium with the addition of 15 g. of air- 

 dry agar. Used with agar for the detection of acidity, it is necessary 

 to have an indicator present. 



Synthetic nitrate medium. A modification of the above is valuable 

 in detecting nitrate reduction in the case of some organisms that do 

 not produce nitrite from nitrate in a peptone medium. 



Adjust to pH 7 by the addition of 

 > NaOH. About 6 ml. normal NaOH 

 required. 



K2HPO4 0.5 g. 



CaCla (anhyd.) 0.5 g. 



MgS04+7H.O 0.2 g. 



Glucose 10 g. 



KNO3 1 g. 



Distilled water 1000 ml. 



To prevent precipitation of calcium phosphate, one or 

 the other of the first two salts listed should be dis- 

 solved separately in a portion of the water and added 

 after the other ingredients have been brought into 

 solution. No adjustment of reaction required. 



D. Media for Anaerobic Bacteria^ 

 Before listing the various media which are to be used for anaerobic 

 bacteria, it is necessary to introduce briefly the related topic — oxida- 

 tion reduction (0/R) potential. 



The 0/R potential required for obligate anaerobes is in general low (Hewitt (1937), 

 Knight (1931), and Reed and Orr (1943).) The usual fluid medium is a complex of 

 active oxidation-reduction systems, but if the medium is prepared from peptone or 

 more simple constituents, usually it is necessary to include special substances to bring 

 the potential to the desired low level. The addition of a small amount (0.1%) of agar 

 will aid in the prevention of diffusion of atmospheric oxygen into the medium, but this 



*This section has been prepared for the Committee by L. S. McClung. 



