History and current taxonomic status of genus Agrobacterium

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 nonpathogenic 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.

Genetic diversity of Agrobacterium species isolated from nodules of common bean and soybean in Brazil, Mexico, Ecuador and Mozambique, and description of the new species Agrobacterium fabacearum sp. nov.

“…The telA sequences were recovered from the genomes of the CNPSo strains sequenced and from the type and reference strains and were used to construct a phylogenetic tree (); the only exception was ‘ A. albertimagni ’ AOL 15 T , as the strain does not have this gene [1] and, as suggested by several studies, can represent a separate genus [20, 23, 49]. Interestingly, the strains were clustered () in the same three groups observed in the MLSA (Figs 2 and 3), confirming that this trait is key for defining the genus.…”

“…Biovar 2 is more distantly related to Agrobacterium species and was designated as Rhizobium rhizogenes and biovar 3 was described as Agrobacterium vitis (currently Allorhizobium vitis ) and includes isolates from grapevine ( Vitis species) [15, 18, 19]. In relation to biovar 1, some genomovars have been classified as new species of Agrobacterium , such as Agrobacterium pusense for G2, Agrobacterium deltaense for G7 and Agrobacterium salinitolerans for G9 [20–22], and the others will probably receive Latin binomial names in the near future [20, 23].…”

Genome Analysis of Endobacterium cerealis, a Novel Genus and Species Isolated from Zea mays Roots in North Spain

“…This occurs in the case of the most recently described genera within the family, Pseudorhizobium, Gellertiella and Georhizobium isolated from water-related environments [ 11 , 12 , 13 ]. However, none of the Rhizobiaceae genera described to date were originally isolated from cereal related sources [ 11 , 12 , 13 , 14 , 15 , 16 , 17 ]. In this work we described the first new genus within family Rhizobiaceae isolated from roots of a cereal and whose type strain RZME27 T is to date the only available strain for this genus.…”

“…The family Rhizobiaceae [ 1 ] belongs to the class Alphaproteobacteria and currently, this family comprises the classical genera Rhizobium [ 2 ], Agrobacterium [ 3 ], Sinorhizobium [ 4 ] (later transferred to Ensifer [ 5 ]), and Allorhizobium [ 6 ] as well as the more recently described genera Shinella [ 7 ], Ciceribacter [ 8 ], Neorhizobium [ 9 ], Pararhizobium [ 10 ], Pseudorhizobium [ 11 ], Gellertiella [ 12 ] and Georhizobium [ 13 ]. Several of these genera contain species originally isolated from legume nodules, such as Rhizobium , Ensifer ( Sinorhizobium ), Allorhizobium , Shinella , Neorhizobium or Pararhizobium [ 14 , 15 , 16 ] and from plant tumours such as Agrobacterium [ 17 ]. However, other genera within this family have not been reported to date as legume endosymbionts, plant endophytes or plant pathogens, such as Ciceribacter , Pseudorhizobium , Gellertiella and Georhizobium [ 11 , 12 , 13 ].…”

Agrobacterium cavarae sp. nov., isolated from maize (Zea mays L.) roots

“…In media containing carbohydrates as carbon sources, members of the genus Agrobacterium produce acids and copious extracellular polysaccharide slime [1]. This genus currently contains pathogenic species able to induce plant tumours or hairy roots and also non-pathogenic species isolated from soil and different plant-related sources [2, 3]. Although some of these species were originally isolated from legume nodules, none of them have been isolated from cereals to date [2, 3].…”