76 



Occurrence of Microorganisms in Soil 



in detail by Woodman. Methane was produced by unheated cul- 

 tures and was probably due to accompanying forms. The thermo- 

 philic organisms occupy an important place among the anaerobic 

 bacteria. 



Probably no other group of bacteria has been so much confused 

 as the aerobic cellulose-decomposing organisms. Many names have 

 been proposed for different members of this group, one organism 



receiving a number of names from dif- 

 ferent investigators. In 1918, Hutch- 

 inson and Clayton reported the isola- 

 tion from the soil of an organism 

 which develops first as a sinuous fila- 

 mentous cell ( 3-10 IX by 0.3-0.4 fi ) and 

 which goes through several phases in 

 its life cycle, terminating in the pro- 

 duction of a spherical body or sporoid. 

 This body differed in a number of re- 

 spects from the true spores of bac- 

 teria. Germination of the sporoid 

 gave rise to a filamentous form which 

 possessed perfect flexibility and was 

 feebly motile, although no flagella 

 were observed. This organism was 

 named Spirochaeta cytophaga. 



A detailed systematic study of vari- 

 ous aerobic cellulose-decomposing bacteria found in the soil has been 

 made by Winogradsky, who divided these organisms into three 

 genera: 



1. Cytophaga: slender, flexible filaments, 3-8 fi long, and pointed 

 at each end; only cellulose can be used as a source of energy; the 

 cellulose is changed into a colloidal gel, colored yellow, orange, rose, 

 red. Four species of this organism were described, including Cyt. 

 hutchinsoni, the organism previously described by Hutchinson and 

 Clayton. 



2. Cellvibrio: slender, bent rods with rounded ends, 2-5 jx long; 

 actively motile, with one flagellum; cellulose decomposition is not 

 invariably specific; cream- to ocher-colored pigment, readily diffus- 

 ing; very abundant, although only two species were described. 



3. Cellfalcicula: spindle- or sickle-shaped cells, not exceeding 2 fi in 

 length, with pointed ends; motile, with one flagellum; paper stained 



Fig. 33. Aerobic, cellulose-de- 

 composing bacterium, Cytophaga 

 lutea ( from Winogradsky ) . 



