48 International Code of Nomenclature 



Recommendation 8a. Sect. 1. Naming of Taxa 



RECOMMENDATION 8a. Authors of names of subdivisions of species of 

 bacteria which are not treated as subspecies (varieties) should attend to the 

 following recommendations and defmitions: 



(1) A strain is made up of the descendants of a single isolation in pure 

 culture. It may be designated in any manner, as by the name of the indi- 

 vidual responsible for its isolation (as Corynebacterium diphtheriae strain 

 Park-Williams); by the name of a locality, by a number, or by some similar 

 laboratory distinguishing mark. "Strain" may also be used to designate cul- 

 tures of bacteria which correspond to cultivated "varieties" (cultivars) of 

 higher plants in having some special economic significance. 



ANNOTATIONS 



Recnmrnendntion 8a (1) . Rule 9 emphasizes the importance of pre- 

 serving the particular strain of a species which was first isolated and 

 studied in the preparation of the species description, i.e., the type 

 culture of the species. 



A particular strain of a species or subspecies may show marked 

 differences in economic significance from other strains or isolations. 

 Corynebacterium diphtheriae strain Park-Williams has long been 

 used for commercial production of diphtheria toxin. The yield of 

 the antibiotic streptomycin varies greatly with the strain of Strepto- 

 myces griseiis used in its production. Strains of organisms which 

 show marked differences in virulence, pigment production, enzyme 

 yield, host specificity, host preference, or other characters may be 

 labeled appropriately. 



Certain mutant strains of microorganisms may require special 

 identification because of their importance in providing a biochemical 

 marker for cell-metabolism studies. For example, by irradiation of 

 a bacterial culture followed by appropriate techniques of isolation, 

 it may be possible to secure a mutant strain that differs from the 

 parent culture in inability to synthesize leucine and thus exhibits a 

 growth requirement for this amino acid in the cultiue medium. An 

 organism having this characteristic may be known as "leucineless 

 strain." 



A strain which originates as a mutant may also be termed a 

 variant, though the term variant does not necessarily indicate a true 

 gene mutation. Variants are constantly arising, such as differently pig- 

 mented sectors in a colony, or a lactose-fermenting mutant in a culture 

 of a non-lactose-fermenting organism. 



