MICRO-ORGANISMS 5 



related to one another. Classification of both families and genera is 

 based exclusively on morphology, whereas that of species may depend 

 partly on morphology but also on physiological characterise i 



In the large and important genus Streptomyces, classification of 

 groups of species seems to be based best on (1) morphology of the 

 sporophores, (2) color of the aerial part of the colony, or (3) combina- 

 tions of these two characteristics. In this genus, spores germinate to 

 form germ tubes, which then develop a colony of substrate mycelium 

 exactly like fungi. The colonies are slower growing than most fungi, 

 are powdery on the surface, and have a strong soil odor. From the 

 substrate mycelium, aerial stalks are formed that branch in a charac- 

 teristic fashion. Ultimate hyphal branches, at least, form spores 

 simultaneously. A study of the spores and their development, using 

 the electron microscope, has shown many interesting species differences 

 in Streptomyces. More and more evidence indicates that these forms 

 should be studied as fungi. 



The actinomycetes produce a great variety of insoluble and water- 

 soluble pigments. Nocardia attacks paraffin, phenol, and other petro- 

 leum-derived materials. Streptomyces forms a wide variety of anti- 

 biotic substances, some of which are of great economic importance 

 like streptomycin, chlorotetracycline, oxytetracycline, tetracycline, 

 chloramphenicol, and erythromycin. Some species are known to 

 transform steroids and to produce vitamin B 12 . As far as we know, all 

 species can be preserved successfully in a lyophilized state provided 

 mature spores are used. 



ALGAE 



Algae are the simplest of the chlorophyllous plants. Probably they 

 were the first photosynthetic organisms in the history of life on earth 

 and are considered the first link in the food chain of life. They are 

 nearly omnipresent and are numerous almost any place that has suf- 

 ficient moisture, such as on tree trunks, soil, rocks, and walls, and of 

 course throughout fresh-water and marine habitats. In addition, 

 certain algae grow in such unusual places as snow or hot springs. 

 Frequently they grow in association with other plants or on mollusks 

 and fish. 



Algae are cellular organisms. The multicellular ones can have a 

 fairly complex structure, but because they have no jacket of sterile 

 cells surrounding the sex organs, they are separated from the mosses 

 and liverworts. A few of the simpler algae are difficult to dist ingoish 

 from protozoa, fungi, or bacteria, but unlike the bacterial groups, the 

 vast majority of algae contain chlorophyll and can thus utilize the 

 energy of sunlight to synthesize organic matter and their own proto- 

 plasm from carbon dioxide, water, and inorganic substances. The 

 numerous exceptions generally are related to other algae by their 

 structure, life history, and storage products; but some organisms are 

 arbitrarily assigned to the algae or protozoa. 



Generally each algal cell — or alga, where unicellular — is either 

 surrounded by a gelatinous sheath or embedded in a gelat inous matrix. 

 The cell wall is composed of cellulose and pectins and occasionally has 

 in it chitin, silica, and tannins. The protoplast contains pigment 

 bodies, nucleus, cytoplasm, and vacuoles. Each cell usually holds 



