Molecular Diversity of nifH Genes from Bacteria Associated with High Arctic Dwarf Shrubs
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Biological nitrogen fixation is the primary source of new N in terrestrial arctic ecosystems and is fundamental to the long-term productivity of arctic plant communities. Still, relatively little is known about the nitrogen-fixing microbes that inhabit the soils of many dominant vegetation types. Our objective was to determine which diazotrophs are associated with three common, woody, perennial plants in an arctic glacial lowland. Dryas integrifolia, Salix arctica, and Cassiope tetragona plants in soil were collected at Alexandra Fiord, Ellesmere Island, Canada. DNA was extracted from soil and root samples and a 383-bp fragment of the nifH gene amplified by the polymerase chain reaction. Cloned genotypes were screened for similarity by restriction fragment length polymorphism (RFLP) analysis. Nine primary RFLP phylotypes were identified and 42 representative genotypes selected for sequencing. Majority of sequences (33) were type I nitrogenases, whereas the remaining sequences belonged to the divergent, homologous, type IV group. Within the type I nitrogenases, nifH genes from posited members of the Firmicutes were most abundant, and occurred in root and soil samples from all three plant species. nifH genes from posited Pseudomonads were found to be more closely associated with C. tetragona, whereas nifH genes from putative alpha-Proteobacteria were more commonly associated with D. integrifolia and S. arctica. In addition, 12 clones likely representing a unique clade within the type I nitrogenases were identified. To our knowledge, this study is the first to report on the nifH diversity of arctic plant-associated soil microbes.
KeywordsNitrogen fixation Molecular ecology Diazotroph
We thank Dr. Greg Henry for logistic support at the Alexandra Fiord site. We thank Mark Thompson of the UNBC sequencing facility for technical service and advice concerning phylogenetic analyses. This research was supported by funding from the Natural Sciences & Engineering Research Council of Canada to K.N.E., with additional logistic support from the Northern Scientific Training Program (Department of Indian and Northern Affairs Canada), the Polar Continental Shelf Project, and the Royal Canadian Mounted Police.
- 2.Chapin, FS, Jefferies, RL, Reynolds, JF, Shaver, GR, Svoboda, J (1992) Arctic plant physiological ecology: a challenge for the future. In: Chapin, FS, Jefferies, RL, Reynolds, JF, Shaver, GR (Eds.) Arctic Ecosystems in a Changing Climate: An Ecophysiological Perspective. Academic Press, San Diego, pp 3–8Google Scholar
- 4.Chein, Y-T, Zinder, SH (1996) Cloning, functional organization, transcript studies, and phylogenetic analysis of the complete nitrogenase structural genes (nifHDK2) and associated genes in the archeaon Methanosarcina barkeri 227. J Bacteriol 178: 143–148Google Scholar
- 12.Larimer, FW, Chain, P, Hauser, L, Lamerdin, J, Malfatti, S, Do, L, Land, ML, Pelletier, DA, Beatty, JT, Lang, AS, Tabita, FR, Gibson, JL, Hanson, TE, Bobst, C, Torres y Torres, JL, Peres, C, Harrison, FH, Gibson, J, Harwood, CS (2004) Complete genome sequence of the metabolically versatile photosynthetic bacterium Rhodopseudomonas palustris. Nat Biotechnol 22: 55–61PubMedCrossRefGoogle Scholar
- 15.Muc, M, Freedman, B, Svoboda, J (1989) Vascular plant communities of a polar oasis at Alexandra Fiord (79°N), Ellesmere Island. Can J Bot 67: 1126–1136Google Scholar
- 18.Shaver, GR, Chapin, FS (1986) Effect of fertilizer on production and biomass of tussock tundra, Alaska, USA. Arct Antarct Alp Res18: 261–268Google Scholar
- 21.StatSoft, Inc. (2002) STATISTICA (data analysis software system), version 6. www.statsoft.comGoogle Scholar
- 22.Van Wijk, MT, Clemmensen, KE, Shaver, GR, Williams, M, Callaghan, TV, Chapin, FS, Cornelissen, JHC, Gough, L, Hobbie, SE, Jonasson, S, Lee, JA, Michelsen, A, Press, MC, Richardson, SJ, Rueth, H (2004) Long-term ecosystem level experiments at Toolik Lake, Alaska, and at Abisko, Northern Sweden: generalizations and differences in ecosystem and plant type responses to global change. Glob Chang Biol 10: 105–123CrossRefGoogle Scholar
- 23.Wall, LG (2000) The actinorhizal symbiosis. J Plant Growth Reg 19: 167–182Google Scholar
- 24.Young, J (1992) Phylogenetic classification of nitrogen-fixing organisms. In: Stacey, G, Burris, RH, Evans, HJ (Eds.) Biological Nitrogen Fixation. Chapman & Hall, New York, pp 43–87Google Scholar