ICSP subcommittee on the taxonomy of rhizobia and agrobacteria

The International Committee for Systematics of Prokaryotes (ICSP), Subcommittee on the Taxonomy of Rhizobia and Agrobacteria is an international working group of microbiologists that aims at establishing the taxonomic nomenclature of bacteria with rhizobial and agrobacterial properties.

The general term ‘rhizobia’ covers all bacteria that induce nodule formation on the roots of a legume host (plant family Fabaceae), where they fix atmospheric nitrogen (N2). Nitrogen fixation by rhizobia in association with legumes can be a major input of nitrogen (N) into natural and agricultural ecosystems and can reduce the need for chemical N fertilizer. There has been extensive research on the diversity of rhizobia over the past 25 years, with the result that many new species and genera have been formally described. Taxonomically, rhizobia represent several lineages within the Proteobacteria, and therefore the term “rhizobia” does not represent a single taxon, but refers to a polyphyletic assemblage of bacterial lineages having similar functions. The symbiosis (sym) genes that enable rhizobial strains to induce N2-fixing nodules on legumes are often encoded on dispensable but transferable genomic elements (plasmids or genomic islands).

The general term ‘agrobacteria’ covers all bacteria that incite – or potentially may incite – the formation of galls or root hypertrophies (crown gall or hairy root disease) by T-DNA transfer to any of a wide range of plant species, including many important agricultural crops. Most of the genes involved in crown gall and hairy root diseases are borne on large conjugative plasmids, the Ti (tumor-inducing) and Ri (root-inducing) plasmids, respectively. There again, these elements are transmissible and can be gained or lost by strains.

This website intends to provide the latest published status on the nomenclature of rhizobia and agrobacteria, as well as practical information for researchers aiming at expanding knowledge in this area. 


List of species known to include strains with rhizobial or agrobacterial phenotypes. A link to List of Prokaryotic names with Standing in Nomenclature (LPSN) for the relevant genera. In addition, a table summarizes the current nomenclature for species included in these genera - those species with known rhizobia or agrobacteria, as well as their non-symbiotic relatives - indicating the type strain and accession numbers for related genomic data; this table is maintained up to date by the Subcommittee members.

List of the current Subcommittee membership, with each member's specialty and contact.

A record of publications relating to the taxonomy of agrobacteria and rhizobia, including the published minutes and recommendations of the Subcommittee and publications of new or emended taxon names. It also features any scientific publication relating to the study of the diversity of taxa within the scope of the Subcommittee.

A space of expression for the members of the ICSP subcommittee (Sc) for the taxonomy of rhizobia and agrobacteria. This blog allows the regular publication of scientific opinions on varied topics related to the Sc's remit. Published articles represent personal views of the members, not the official opinion of the Sc.

Some members of the Sc published a paper “Guidelines for the description of rhizobial symbiovars”. In this paper, they discussed the requirements and guidelines to describe symbiovars, propose a set of rules, provide a list of all symbiovars published so far, and offer a mechanism to maintain a list in the future.