Assembly and transfer of tripartite integrative and conjugative genetic elements

T.L. Haskett; J.J. Terpolilli; A. Bekuma; G.W. O’Hara; J.T. Sullivan; P. Wang; C.W. Ronson; J.P. Ramsay

doi:10.1073/pnas.1613358113

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Assembly and transfer of tripartite integrative and conjugative genetic elements

Journal article

Open access

Peer reviewed

Assembly and transfer of tripartite integrative and conjugative genetic elements

T.L. Haskett, J.J. Terpolilli, A. Bekuma, G.W. O’Hara, J.T. Sullivan, P. Wang, C.W. Ronson and J.P. Ramsay

Proceedings of the National Academy of Sciences, Vol.113(43), pp.12268-12273

2016

DOI: https://doi.org/10.1073/pnas.1613358113

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Abstract

Integrative and conjugative elements (ICEs) are ubiquitous mobile genetic elements present as "genomic islands" within bacterial chromosomes. Symbiosis islands are ICEs that convert nonsymbiotic mesorhizobia into symbionts of legumes. Here we report the discovery of symbiosis ICEs that exist as three separate chromosomal regions when integrated in their hosts, but through recombination assemble as a single circular ICE for conjugative transfer. Whole-genome comparisons revealed exconjugants derived from nonsymbiotic mesorhizobia received three separate chromosomal regions from the donor Mesorhizobium ciceri WSM1271. The three regions were each bordered by two nonhomologous integrase attachment (att) sites, which together comprised three homologous pairs of attL and attR sites. Sequential recombination between each attL and attR pair produced corresponding attP and attB sites and joined the three fragments to produce a single circular ICE, ICEMcSym1271. A plasmid carrying the three attP sites was used to recreate the process of tripartite ICE integration and to confirm the role of integrase genes intS, intM, and intG in this process. Nine additional tripartite ICEs were identified in diverse mesorhizobia and transfer was demonstrated for three of them. The transfer of tripartite ICEs to nonsymbiotic mesorhizobia explains the evolution of competitive but suboptimal N2-fixing strains found in Western Australian soils. The unheralded existence of tripartite ICEs raises the possibility that multipartite elements reside in other organisms, but have been overlooked because of their unusual biology. These discoveries reveal mechanisms by which integrases dramatically manipulate bacterial genomes to allow cotransfer of disparate chromosomal regions.

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Title: Assembly and transfer of tripartite integrative and conjugative genetic elements
Authors/Creators: T.L. Haskett (Author/Creator) - Murdoch University
J.J. Terpolilli (Author/Creator) - Murdoch University
A. Bekuma (Author/Creator) - Murdoch University
G.W. O’Hara (Author/Creator) - Murdoch University
J.T. Sullivan (Author/Creator)
P. Wang (Author/Creator) - Murdoch University
C.W. Ronson (Author/Creator) - University of Otago
J.P. Ramsay (Author/Creator) - Curtin University
Publication Details: Proceedings of the National Academy of Sciences, Vol.113(43), pp.12268-12273
Publisher: National Academy of Sciences
Identifiers: 991005542742707891
Murdoch Affiliation: Centre for Rhizobium Studies
Language: English
Resource Type: Journal article

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Collaboration types: Domestic collaboration; International collaboration
Citation topics: 3 Agriculture, Environment & Ecology; 3.97 Plant Pathology; 3.97.892 Rhizobium-Legume Symbiosis
Web Of Science research areas: Microbiology
ESI research areas: Microbiology