364 Microbes and You 



from these mycelial storehouses. The importance of molds in the 

 decomposition of cellulose, that relatively undigestible material of 

 which plants are composed, has recently been reaffirmed. By add- 

 ing cellulose to soils, a prompt increase in the number of fungi will 

 be registered. Spoilage of cellulose-containing materials by fungi 

 was amply demonstrated during World War II, especially in trop- 

 ical and sub-tropical countries. Lignin, which is an essential part 

 of woody tissue, is also attacked by molds. Unless cellulose, lignin, 

 and starch are decomposed by biological action, the chemical ele- 

 ments found in these complex materials would be bound up and 

 unavailable for use by other plants and by animals. 



SPOILAGE 



While most bacteria tend to spoil foods which are neutral or 

 nearly neutral in reaction, molds thrive in environments where the 

 pH is too low for usual bacterial activity. Organic acids which 

 bacteria in general cannot tolerate, may be metabolized by molds 

 as a source of carbon and energy, and these acids may be oxidized 

 to carbon dioxide and water. As the acids oxidize, the pH may 

 rise to the point where bacterial growth may become possible. 



The low food and moisture requirements of molds will allow 

 them to grow on optical glass, which they are capable of etching. 

 Such glass stored in moist areas has been known to be ruined by 

 the growth of fungi. Mildew damage to tentage that is stored 

 without adequate drying is a constant problem with the armed 

 forces and with circuses. Warm damp weather encourages mold 

 growth on the leather of shoes, on paper, and on cloth. Nylon and 

 rayon, however, are resistant to mold action. 



High osmotic pressure is little deterrent to fungi, as evidenced 

 by mold growth on the surface of jellies and jams containing a high 

 sugar content. As long as air is excluded, however, molds cannot 

 grow on these products. Spoilage of bread and other starchy foods 

 by Rhizopus species is a common problem during the summer 

 months, and the green fuzz seen on decaying fruits is usually a 

 member of the Penicillium genus. 



