

4 MISCELLANEOUS PUBLICATION 955, U.S. DEPT. OF AGRICULTURE 



include all the well-known bacteria of medical and industrial useful- 

 ness. The other six orders are largely unknown except to a few 

 specialists. 



No one knows how many species of bacteria there are. In Bergey's 

 manual (4.) about 1,500 species are listed in 208 genera. 



Fortunately most bacteria are harmless or beneficial. It is unfortu- 

 nate that most people's knowledge of bacteria is limited to those that 

 cause disease. Almost everyone has been awed by stories of the Black 

 Death, which decimated the populations of entire towns in Europe a 

 few centuries ago, by the white plague, and by epidemics of diphtheria, 

 typhoid fever, scarlet fever, and cholera. These diseases still rage in 

 underdeveloped areas, and their still-present dangers must not be 

 forgotten. 



Even in ancient times bacteria as well as other micro-organisms were 

 used to benefit mankind. Before food was preserved by refrigeration 

 and before canning had been developed, men learned to ferment 

 shredded cabbage to sauerkraut ; milk to yoghurt, kumiss, and leben ; 

 milk curd to various cheeses; cucumbers and other vegetables to 

 pickles ; and wine and other alcoholic solutions to vinegar. 



These processes have been developed into modern industries. We 

 have learned to domesticate a great variety of micro-organisms and to 

 induce them to make products of value other than food. Among the 

 products of bacterial fermentation, apart from foods, are acetic acid, 

 lactic acid, acetone, butyl alcohol, 2-ketogluconic acid, alpha-keto- 

 glutaric acid, dextran, vitamin B 12 , various enzymes, and antibiotics. 

 In addition, vaccines, antisera, and antitoxins are produced in quan- 

 tities sufficient to protect the populations of the world against the dread 

 diseases of past generations. 



ACTINOMYCETES 



Actinomycetes are considered to be bacteria by some microbiologists 

 and to be fungi by others. Still others consider them to be a distinct, 

 isolated group, but related to both bacteria and fungi. 



Actinomycetes include forms found in soil and water, although a 

 few are animal and plant pathogens. By far the largest group pro- 

 duces branched mycelium and spores, which function similarly to 

 asexual spores in fungi. The spores are not heat resistant as in the 

 bacterial genera Bacillus and Clostridium, but they function as units 

 of reproduction as well as cells to carry the species through periods of 

 adverse growth conditions, such as drying. Like bacteria, the spores 

 and the mycelium are never more than 2 or 3 microns in diameter. 

 Like bacteria, various genera are attacked by numerous phages. In 

 some forms sporangia develop, and the spores may be motile by means 

 of flagella. Whether or not sexual reproduction occurs is not yet con- 

 clusively proved. 



According to Bergey's manual (4), there are four families in the 

 order Actinomycetales— Mycobacteriaceae, Actinomycetaceae, Strep- 

 tomycetaceae, and Actinoplanaceae. These families embody nine 

 genera and a considerable number of species, with the largest number 

 m Nocardia and Streptomyces. The first family may be considered 

 as more removed from the order than the last three, which are closely 



