PROTOTROPHIC BACTERIA 



I8 7 



some object. This filament of cells is surrounded by a thin 

 sheath. Reproduction takes place by means of gonidia. 

 The gonidia are formed from the terminal cells of the filament 

 and are liberated in the usual way. Certain nonfilamentous 

 forms, such as Beggiatoa, are well 

 known. Both of these forms make 

 use of hydrogen sulphide as a food, 

 oxidizing it to water and elemental 

 sulphur. These sulphur granules are 

 stored in the cell itself. These bac- 

 teria do not grow in highly nutritious 

 culture media, but are able to obtain 

 their food from relatively simple sub- 

 stances by means of the energy which 

 is obtained by the oxidation of the 

 sulphuretted hydrogen. Their carbon 

 may be obtained from the air or FIG. 45. Sulphur bacteria. 



f ,, , .... (i) Thiospirillum Wino- 



from small traces of formic or propn- gradskii (a) Beggiatoa 

 onic acids. Nitrogen may be ob- 

 tained from the air or from ammonia. 

 In the synthesizing of organic material they work indepen- 

 dent of the rays of sunlight. 



Another group of these sulphur bacteria are colored purple 

 by a coloring matter known as bacteriopurpurin, which acts 

 in a way similar to the chlorophyll of green plants. These 

 bacteria are large micrococci which have the coloring matter 

 evenly distributed throughout the protoplasm. They have 



alba. X 2000. After Cor- 

 sini. (Lipman). 



