Classification and nomenclature of Agrobacterium and Rhizobium

Farrand et al. [Int J Syst Evol Microbiol 53 (2003), 1681-1687] have presented a critique of the proposal of Young et al. [Int J Syst Evol Microbiol 51 (2001), 89-103] to revise the nomenclature and classification of RHIZOBIUM: They argued that Young et al. (2001) are mistaken in their reclassification of all Agrobacterium species within Rhizobium, and that the resulting nomenclatural revision is 'unnecessary and unwarranted'. These objections arise because the authors appear not to understand the role of formal nomenclature, and fail to distinguish between formal and special-purpose nomenclatures (Bacteriological Code, 1990 Revision). The arguments set out by Farrand et al. (2003) can be addressed in terms of (1) the taxonomic status of the genera Agrobacterium and Rhizobium; (2) the status of species and biovars and their nomenclature; and (3) the role of transmissible genomic elements in classification and nomenclature. Finally, an attempt is made to unravel the confusion underpinning their discussion with a consideration of the relationship between formal and special-purpose nomenclatures.