History and current taxonomic status of genus Agrobacterium

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Abstract

The genus Agrobacterium was created a century ago by Conn who included it in the family Rhizobiaceae together with the genus Rhizobium. Initially, the genus Agrobacterium contained the non-pathogenic species Agrobacterium radiobacter and the plant pathogenic species Agrobacterium tumefaciens and Agrobacterium rhizogenes. At the end of the past century two new pathogenic species, Agrobacterium rubi and Agrobacterium vitis, were added to the genus. Already in the present century these species plus Agrobacterium larrymoorei were reclassified into genus Rhizobium. This reclassification was controversial and for a time both genus names were used when new species were described. Few years ago, after a taxonomic revision based on genomic data, the old species A. rhizogenes was maintained in the genus Rhizobium, the old species A. vitis was transferred to the genus Allorhizobium and several Rhizobium species were transferred to the genus Agrobacterium, which currently contains 14 species including the old species A. radiobacter, A. tumefaciens, A. rubi and A. larrymoorei. Most of these species are able to produce tumours in different plants, nevertheless the genus Agrobacterium also encompasses non-pathogenic species, one species able to nodulate legumes and one human pathogenic species. Taking into account that the species affiliations to five Agrobacterium genomospecies have not been determined yet, an increase in the number of species within this genus is expected in the near future.

Section snippets

The Agrobacterium taxonomy in the past century

The genus Agrobacterium was created by Conn [9] who included it within the family Rhizobiaceae [8] together with the genus Rhizobium [14]. In the 5th edition of the Bergey’s Manual of Determinative Bacteriology, the species included into the genus Agrobacterium were Agrobacterium radiobacter, Agrobacterium tumefaciens and Agrobacterium rhizogenes. In the 6th edition of this Manual the plant tumorigenic species Agrobacterium rubi [17], [48] was included, being differentiated from A. tumefaciens

The taxonomy of genus Agrobacterium from 2000 onwards

The most relevant and conflictive change in the taxonomic status of genus Agrobacterium took place in year 2001 when Young et al. [60] proposed the reclassification of the complete genus Agrobacterium into the genus Rhizobium. This reclassification was based on the results of Sawada et al. [43] and, therefore, the Agrobacterium species were reclassified as Rhizobium radiobacter, Rhizobium rhizogenes, Rhizobium rubi and Rhizobium vitis. The reclassification, which was based on the rrs gene

Aknowledgements

This work was supported by MINECO (Spanish Central Government) Grant AGL2013-48098-P to EV. EM was granted by a postdoctoral contract associated to this project.

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    Current affiliation: ICAAM – Instituto de Ciências Agrárias e Ambientais Mediterrânicas, Laboratório de Microbiologia do Solo, Universidade de Évora.

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