MICRO-ORGANISMS 



I WHAT THEY ARE, WHERE THEY GROW, 



I WHAT THEY DO 



By C. K. Benja^^c, 1 Crops Research Division, and W. O. Hayhes and C. W. 



Hesseltine, Northern Utilization Research and Development D 

 Agricultural Research Service 



The world literally teems with micro- orpin isms of all kind-. T! 

 include viruses, bacteria, actinomycetes, algae, protozoa, fungi 

 (also yeasts), and lichens. Some micro-organisms are ubiquitous, 

 airborne forms that are much more difficult to avoid than to find. 

 Others are so restricted in habitat that they may be found only on 

 a particular part of the body of a single species of beetle. 



It is estimated that there are 100,000 species of fungi alone. Fungi 

 range from such ubiquitous forms as Cladosporium, which grows 

 throughout the world on all kinds of plant material, to such special- 

 ized forms as Chitonomyces, which has had 16 species reported on a 

 single aquatic beetle. Of these 16 species, 6 are restricted to male 

 beetles and 9 to female. Not only are the species restricted to a siinj 

 host and sex but they are also restricted to a single part of the hosl 

 body. 



Some kinds of bacteria have been found several miles above the 

 earth surface or below in the mud of ocean floors. Hoih bacteria 

 and blue-green algae grow in hot springs at temperatures of 75° (\. 

 and bacteria have been isolated from antarctic ice. Certain molds 

 grow best on or near receding edges of snow on mountains. Sonic 

 lichens normally grow on seemingly bare rock. Whatever the habi- 

 tat, generally a variety of micro-organisms can be found. 



In this publication these micro-organisms are described, references 

 are made to their classification, some of their uses are indicated, and 

 authoritative sources of information are cited. 



VIRUSES AND RICKETTSIAE 



Viruses and rickettsiae are members of the taxonomic class ap- 

 propriately named Microtatobiotes, which means literally "smallest 

 living things." Most viruses cannot be seen with the ordinary light 

 microscope; they are ultramicroscopic and are only seen by means of 

 an electron microscope. They pass through filters designed to retain 

 bacteria, and in the past they were often spoken of as filterable viruses, 



1 Formerly with Northern Utilization Research and Development Division. 



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