Z CULTIVATION AND GROWTH 



gum arable, or polyvinyl alcohol in the medium (334) may be neces- 

 sary. 



Two major objections attach to the use of surface culture for fungi. 

 The cells of the developed mat are not only visibly of different types — 

 aerial and submerged growth — but also are exposed to different en- 

 vironmental conditions. Aerial hyphae are remote from the nutrient 

 supply and are bathed in the atmosphere; the lower cells, by contrast, 

 are in close contact with nutrients and with soluble metabolic products 

 but suffer from a partially anaerobic environment (167). Examination 

 of submerged hyphae in such a culture shows them to be highly 

 vacuolated. The culture as a whole is probably always deficient in 

 oxygen. This deficiency is shown by the favorable effect on sugar 

 utilization of an increase in surface : volume ratio (208) and by the 

 effect, mentioned below, of aeration on growth rate of most fungi. 



The commonest and most useful laboratory-scale aerated culture 

 apparatus is the shaker, first thoroughly studied by Kluyver and Per- 

 quin (161). Flasks are mounted on a platform which is either rotated 

 rapidly or moved horizontally with a reciprocating motion. Problems 

 of design are considered by Shu and Johnson (270), Paladino (230), and 

 Chain and Gualandi (54). 



Representatives of all the major groups of fungi and of the genus 

 Streptomyces have been grown successfully in stirred or shake culture. 

 The growth rate is usually at least double that of the same organism 

 in surface culture (1, 61, 162, 286, 319, 335), although some fungi do 

 not show this effect (14, 268) and some grow so poorly that the method 

 cannot be used for them. One of the chief advantages, apart from 

 more rapid growth, is that shaker-grown mycelium is usually homo- 

 geneous enough to be used directly in respirometric and other meta- 

 bolic studies. 



In shake culture each colony is exposed to a uniform environment 

 in all spatial directions; hence the typical colony is a globose structure. 

 Colonial morphology varies, however, with the species — even within 

 a genus — and with the medium (48). Sporulation is usually, although 

 not always, suppressed — another factor of homogeneity. Microscopic 

 characteristics of the mycelium are also affected by aeration and agita- 

 tion (76, 83). 



Although a shaken culture has a measurably higher content of dis- 

 solved oxygen and rate of oxygen diffusion than a still culture (283), 

 for certain purposes a still higher rate of oxygen supply may be de- 

 sirable (249, 252). This usually arises when a high concentration of 

 a readily utilizable carbon source is employed; the peak oxygen de- 

 mand under specified conditions is 16 mM oxygen per liter per hour 



