114 > Comparatwe Animal Physiology 



early, and heterotrophic animals were derived from autotrophs, perhaps from 

 pigmented flagellates (chlorophytes). 



The carbon and nitrogen requirements of many bacteria and flagellates 

 have been examined. -^' •^"- **-• ^■^' ^"^ In general, the ability to use light or 

 inorganic reactions to provide energy for COo reduction goes with the ability 

 to use nitrate or ammonia (rarely atmospheric nitrogen). Conversely, organ- 

 isms which require fatty acids or sugars as carbon sources also need amino 

 acid nitrogen. However, among flagellates such as the genus Euglena there 

 are exceptions (Table 19). An organism which can use simple nitrogen or 

 carbon sources can also use more complex sources; one which can use nitrate 

 can also use ammonia and amino acids. Only a few phototrophic organisms 

 require amino nitrogen, and only a few protozoans which require organic 

 acids or sugars for carbon can use nitrate or ammonia; many yeasts are in the 

 latter category. 



CARBON REQUIREMENTS 



Phototrophic green flagellates (chloroflagellates) reduce COo directly in 

 hght and use organic acids or sugars for energy in the dark. The rate of photo- 

 synthesis is affected by the hydrogen ion concentration and the inorganic 

 elements in the medium. Euglena stellata, for example, requires a high con- 

 centration of calcium. -"' There is some disagreement regarding the forms of 

 nitrogen required by various flagellates, largely because of differences in min- 

 erals in culture media, strains of species, and other conditions.-'** 



It has been postulated that colorless flagellates, leucophytes, were derived 

 from chlorophytes by the loss of chlorophyll from their plastids. The leuco- 

 phytes and the chlorophytes in the dark can use organic acids, particularly 

 acetic to myristic, and some can use alcohols which are first converted to the 

 corresponding acids. Pringsheim ^^^ described the culture of some twenty 

 different leucophytes on acetate. The effects of various organic acids on 

 growth of flagellates were summarized by Trager. ^'^^ Polytovia iivella uses 

 acetate or butyrate but not sugar.''- The colorless alga Prototheca uses satur- 

 ated fatty acids up to palmitic, except formic acid; it does not use dicarboxylic 

 acids but can use some alcohols. "^ Sugars are used by many flagellates. 

 Trypanosoma hrucei, for example, ferments sugars in the following series: 

 glucose > mannose > maltose > fructose > galactose, but does not ferment 

 arabinose, xylose, lactose or sucrose. ^* Differences in sugar utilization may 

 result in part from enzymatic differences and in part from limited permeability. 



Chilomonas paramecinm is a colorless flagellate which has remarkable 

 powers of synthesis. It multiplies well, dividing three to four times daily in a 

 medium of acetate or glycine as the only carbon source; it grows better with 

 thiamine and iron than without them. Sulfur stimulates fission, and in the 

 absence of sulfur fat accumulates and the culture eventually dies out. It has 

 been claimed by some authors,^"' ^^' ^^- ^°' ^^'^ but not by others,'^^ that 

 Chilomonas can also grow in the dark with COo as its sole source of carbon; 

 growth under these conditions is less than in acetate and a trace of silicon is 

 necessary. There is an optimal COo tension and bacterial contamination has 

 been excluded, also possible oxidation of ammonia. 



It is probable that true protozoans were derived from leucophytes. Some 

 Protozoa are unable to survive on organic compounds in solution, but rather 



