Detection of Flagellar Variants and Mutants 



Flagellar variants of bacteria which show differences in motility 

 may be isolated by plating in semisolid agar. The most convenient 

 technique is to streak plates of solid agar with the culture and a 

 thin layer (about 7 ml. for a 15 cm. plate) of semisolid agar (0.3- 

 0.5% agar) poured on top. Sometimes better results are gotten by 

 making proper dilutions of the culture and inoculating the melted 

 semisolid agar before it is poured on the solid agar. Plates made 

 by either of these two methods can be turned over and otherwise 

 handled like ordinary solid agar plates. Colonies of bacteria with 

 normal peritrichous flagella tend to spread most widely. Colonies 

 of bacteria with peritrichous flagella of any other shape tend to 

 spread less widely, if at all. Colonies of polar flagellated bacteria 

 with normal flagella spread less widely than those of peritrichous 

 flagellated bacteria with normal flagella. 



Detection of spontaneous mutants with greater motility than 

 the parent strain is best accomplished by making a heavy streak 

 across the middle of a soHd agar plate followed by a thin layer of 

 semisolid agar. Mutants with greater motility than the parent strain 

 show up after a variable length of incubation (up to 20 days) as 

 outshoots from the main streak. 



17 



