MICRO-ORGANISMS 7 



Some algae are readily used in culture studies. Notable are certain 

 of the unicellular green algae, such as members of the genus ChloreV'i. 

 which have been utilized widely for physiological studies. Certain 

 green algae produce sterols and vitamins in addition to their chloro- 

 phyll, carotenes, carbohydrates, proteins, and fats. Favorable results 

 have been obtained in their use as food and feed supplements, as 

 reported by Morimura and Tamiya (23) . Under proper conditions of 

 illumination and agitation, some algae also grow well in deep-tank 

 fermentors, as shown by Pruess et al. (25). A pertinent reference to 

 algal culture is the monograph edited by Burlew (5). 



PROTOZOA 



Among animals, only protozoa are unicellular and for this reason 

 are placed in a separate phylum. "Within a single protozoan cell all 

 life functions are carried out that are found in the Metazoa or higher 

 animals. Only a few protozoa are large enough to be observed with 

 the naked eye. Approximately 15,000 to 20,000 species of protozoa 

 are known (18). Unlike bacteria and many fungi, most studies on 

 protozoa have been made on material not freed of other protozoa or 

 bacteria. 



Free-living protozoa are chiefly found in water, both fresh and salt, 

 at temperatures ranging from freezing to 70° C, and to a less extent 

 in soil and decaying organic material. During unfavorable growth 

 conditions, cysts are formed that allow the organism to survive until 

 growth conditions are again favorable. 



Many other protozoa live in or on other organisms. A few protozoa 

 have been isolated and grown in pure culture, but extremely complex 

 nutritional conditions are required for growth. Defined culture 

 media are very complex. The ciliate Tetrahymena has been extensively 

 studied for its growth requirements and nutrition and has been used 

 for the assav of some amino acids. Culture media for the growth of 

 protozoa need not necessarily be liquid. We have seen amebae, flagel- 

 lates, and ciliates grown on an agar medium. In some instances a 

 semisolid medium for small ciliates is preferred to a solid medium. 



Like the more primitive micro-organisms in other groups, some 

 protozoa cannot be readily distinguished from algae. The genus 

 Euglena, which is motile and holophytic (able to use carbon dioxide 

 and light to manufacture carbohydrates), is studied by both proto- 

 zoologists and algologists. Also, the Myxomycetes is treated in text- 

 books on mycology and on protozoology. 



The protozoa have three kinds of locomotion. In some, for example 

 amebae, temporary projections of part of the cytoplasm, called the 

 pseudopodia, are formed. Others swim by means of a flagellum. which 

 is a filamentous extension of the cytoplasm that is highly flexible and 

 so fine that it is often difficult to see even under a microscope. The 

 third kind of locomotion is by cilia, which are rather short projections 

 of the ectoplasm. 



Most protozoa reproduce asexually by binary fission, which takes 

 place longitudinally, although many ciliates divide transversely dur- 

 ing reproduction. Binary fission is the division of the single protozoan 

 cell or body into two nearly equal daughter cells. In some, multiple 



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