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Environ Microbiol Rep. 2017 Jun;9(3):223-238. doi: 10.1111/1758-2229.12502. Epub 2017 Jan 27.

The oil-contaminated soil diazotroph Azoarcus olearius DQS-4T is genetically and phenotypically similar to the model grass endophyte Azoarcus sp. BH72.

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Department of Biochemistry and Molecular Biology, Universidade Federal do Parana, Curitiba, Parana, 81531-980, Brazil.
Laboratory of Gene Expression Regulation, Instituto Carlos Chagas, Fiocruz-PR, Curitiba, Paraná, 81350-010, Brazil.
Department of Microbial Biochemistry and Genomics, Instituto de Investigaciones Biológicas Clemente Estable (IIBCE), Montevideo, 11600, Uruguay.
Department of Biological Sciences, University of Wisconsin - Milwaukee, WI, 53211, USA.
Division of Plant Science and Biochemistry, C. S. Bond Life Science Center, University of Missouri, Columbia, MO, 65211, USA.
Embrapa Agrobiologia, Seropédica, Rio de Janeiro, 23891-000, Brazil.
Laboratory of Microbiology, Department of Seafood Science, National Kaohsiung Marine University, Kaohsiung City, 811, Taiwan.
The James Hutton Institute, Invergowrie, Dundee, DD2 5DA, UK.


The genome of Azoarcus olearius DQS-4T , a N2 -fixing Betaproteobacterium isolated from oil-contaminated soil in Taiwan, was sequenced and compared with other Azoarcus strains. The genome sequence showed high synteny with Azoarcus sp. BH72, a model endophytic diazotroph, but low synteny with five non-plant-associated strains (Azoarcus CIB, Azoarcus EBN1, Azoarcus KH32C, A. toluclasticus MF63T and Azoarcus PA01). Average Nucleotide Identity (ANI) revealed that DQS-4T shares 98.98% identity with Azoarcus BH72, which should now be included in the species A. olearius. The genome of DQS-4T contained several genes related to plant colonization and plant growth promotion, such as nitrogen fixation, plant adhesion and root surface colonization. In accordance with the presence of these genes, DQS-4T colonized rice (Oryza sativa) and Setaria viridis, where it was observed within the intercellular spaces and aerenchyma mainly of the roots. Although they promote the growth of grasses, the mechanism(s) of plant growth promotion by A. olearius strains is unknown, as the genomes of DQS-4T and BH72 do not contain genes for indole acetic acid (IAA) synthesis nor phosphate solubilization. In spite of its original source, both the genome and behaviour of DQS-4T suggest that it has the capacity to be an endophytic, nitrogen-fixing plant growth-promoting bacterium.

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