FOOD REQUIREMENTS OF BACTERIA 55 



is rapidly used by bacteria. The speed with which they decom- 

 pose material is great at first and later slows down or comes to a 

 complete stop unless the accumulation of their by-products is 

 prevented. 



The food required by each bacterial cell for building material 

 is not great, for it would take one billion six hundred million 

 colon bacilli to weight approximately one milligram. The waste 

 products and repair material would make the cellular require- 

 ments slightly higher than this, but the figures are sufficiently 

 accurate to indicate that the actual quantity needed for building 

 material for one cell is exceedingly small. 



The quantity required for energy is greater and varies with 

 different organisms. Those which only partly digest their food 

 leave most of their energy in the by-product. For instance, bac- 

 teria which completely oxidize sugar to carbon dioxid will obtain 

 thirty times as much energy from one gram of grape sugar as 

 others will which change it only to alcohol. 



Kinds of Foods Required. — Bacteria feed upon a great va- 

 riety of substances. The sulfur, iron, and nitrifying bacteria are 

 able to live upon mineral nutrients. The sulfur organisms ob- 

 tain their energy through the oxidizing of sulfur dioxid to sul- 

 furic acid. The nitrifiers oxidize ammonia to nitrites and then 

 to nitrates. Both classes likewise obtain their building material 

 from simple inorganc compounds. Hence, they can live without 

 plant or animal tissue and in the absence of sunlight. Therefore, 

 they were probably the first inhabitants of this globe. The ma- 

 jority of bacteria cannot live upon inorganic compounds, but like 

 animals they require more complex foods. The ordinary decay 

 bacteria will thrive on any plant and animal tissue. Woody 

 fiber, bone, horn, and proteins of all kinds are rather rapidly 

 consumed by them. Other organisms, as for instance the one 

 causing tuberculosis, are more particular in their food require- 

 ment, growing best on blood and body extracts. Others, as for 

 instance the leprosy organism, appear to grow only in living tissue. 



Those bacteria which require neither organic carbon nor or- 

 ganic nitrogen, but live as do the higher plants upon the minerals. 



