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BMC Genomics. 2015 May 2;16:348. doi: 10.1186/s12864-015-1576-3.

Genomic features separating ten strains of Neorhizobium galegae with different symbiotic phenotypes.

Author information

1
Department of Food and Environmental Sciences, University of Helsinki, Viikinkaari 9, 00790, Helsinki, Finland. janina.osterman@helsinki.fi.
2
Department of Environmental Sciences, University of Helsinki, Viikinkaari 2a, 00790, Helsinki, Finland. janina.osterman@helsinki.fi.
3
Department of Food and Environmental Sciences, University of Helsinki, Viikinkaari 9, 00790, Helsinki, Finland. seyed.mousavi@helsinki.fi.
4
Department of Environmental Sciences, University of Helsinki, Viikinkaari 2a, 00790, Helsinki, Finland. seyed.mousavi@helsinki.fi.
5
Institute of Biotechnology, University of Helsinki, Viikinkaari 9, 00790, Helsinki, Finland. patrik.koskinen@helsinki.fi.
6
Institute of Biotechnology, University of Helsinki, Viikinkaari 9, 00790, Helsinki, Finland. lars.paulin@helsinki.fi.
7
Department of Environmental Sciences, University of Helsinki, Viikinkaari 2a, 00790, Helsinki, Finland. kristina.lindstrom@helsinki.fi.

Abstract

BACKGROUND:

The symbiotic phenotype of Neorhizobium galegae, with strains specifically fixing nitrogen with either Galega orientalis or G. officinalis, has made it a target in research on determinants of host specificity in nitrogen fixation. The genomic differences between representative strains of the two symbiovars are, however, relatively small. This introduced a need for a dataset representing a larger bacterial population in order to make better conclusions on characteristics typical for a subset of the species. In this study, we produced draft genomes of eight strains of N. galegae having different symbiotic phenotypes, both with regard to host specificity and nitrogen fixation efficiency. These genomes were analysed together with the previously published complete genomes of N. galegae strains HAMBI 540T and HAMBI 1141.

RESULTS:

The results showed that the presence of an additional rpoN sigma factor gene in the symbiosis gene region is a characteristic specific to symbiovar orientalis, required for nitrogen fixation. Also the nifQ gene was shown to be crucial for functional symbiosis in both symbiovars. Genome-wide analyses identified additional genes characteristic of strains of the same symbiovar and of strains having similar plant growth promoting properties on Galega orientalis. Many of these genes are involved in transcriptional regulation or in metabolic functions.

CONCLUSIONS:

The results of this study confirm that the only symbiosis-related gene that is present in one symbiovar of N. galegae but not in the other is an rpoN gene. The specific function of this gene remains to be determined, however. New genes that were identified as specific for strains of one symbiovar may be involved in determining host specificity, while others are defined as potential determinant genes for differences in efficiency of nitrogen fixation.

PMID:
25933608
PMCID:
PMC4417242
DOI:
10.1186/s12864-015-1576-3
[Indexed for MEDLINE]
Free PMC Article

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