Heterotrophic Bacteria 



69 



colonies ha\e no surrounding zone and ajc recognized only by their 

 granular structure. The occurrence of dilFerent spore-forming bac- 

 teria in the soil is illustrated in Table 12. 



Table h2. Occiurenck of Spoue-Forming Bacteria in Different Soils 

 (from Ford rt al.) 



Non-Spore-Forming Bacteria. The aerobic, heterotrophic, non- 

 spore-forming bacteria usually produce punctiform colonies on agar 

 and gelatin; they are chromogenic or nonchromogenic, motile or non- 

 motile; some liquefy gelatin rapidly, whereas others do it only slowly 

 or not at all. The most important representative of the group of 

 rapid-liquefying organisms is Pseudomonas fliiorescens. The whole 

 group is often spoken of as the fliiorescens group, although many of 

 the organisms never produce any fluorescence. 



Conn divided these organisms into five groups on the basis of 

 their growth upon synthetic media: 



1. Organisms forming small short rods, usually less than 0.5 /x in 

 diameter, nonmotile or having one or possibly two polar flagella; no 

 tendency to change in morphology but very variable in physiology, 

 such as liquefaction of gelatin and gas formation from nitrate. Bac- 

 terium parviilitm belongs to this group. 



2. Organisms that appear, for a day or two after inoculation on 

 a new medium, as small short rods, less than 0.5 /x in diameter, then 



