Presentation Title

Interactions Between Species of Rhizobium in the Rhizobia-Legume Mutualism

Faculty Mentor

Dr. Michelle Lum

Start Date

18-11-2017 2:15 PM

End Date

18-11-2017 3:15 PM

Location

BSC-Ursa Minor 66

Session

Poster 3

Type of Presentation

Poster

Subject Area

biological_agricultural_sciences

Abstract

Rhizobia bacteria provide leguminous plants useable nitrogen through their capability to fix atmospheric nitrogen (N2) into ammonia (NH3). Specifically, rhizobia fix nitrogen in nodules, specific root structures, and receive carbohydrates from the plant in a reciprocally beneficial symbiosis. Nitrogen fixation is energetically costly to rhizobia as it uses resources that could be used towards growth and reproduction. Therefore, natural selection favors ‘cheaters’; rhizobia living in nodules that fix less nitrogen. To maintain this symbiosis, plants must favor rhizobia that fix the most nitrogen and/or use sanctions to penalize ‘cheaters’. I am investigating this relationship by isolating rhizobia and observing their interactions between each other and Pisum sativum (pea). Five bacterial strains were isolated from nodules of Lupinus sp. and P. sativum. 16S rDNA analysis identified four of the strains as Rhizobium leguminosarum and the other as R. rhizogenes. Nodulation assays showed that R. rhizogenes and one of the R. leguminosarum strains do not nodulate pea. Successful nodulating strains resulted in healthy green plants with pink nodules, however co-inoculation with nodulating and non-nodulating strains resulted in white nodules and yellow leaf coloration signifying stress. Furthermore, biofilm production was found to differ among strains of R. leguminosarum. All strains were resistant to ampicillin, and green fluorescent protein (GFP) and mCherry fluorescent markers were introduced into the bacteria. This fluorescence will be used to identify bacteria in co-inoculated pea nodules to observe occupancy patterns. This study will increase our understanding of the interactions between agriculturally applied bacterial bio-fertilizers and naturally occurring soil rhizobia.

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Nov 18th, 2:15 PM Nov 18th, 3:15 PM

Interactions Between Species of Rhizobium in the Rhizobia-Legume Mutualism

BSC-Ursa Minor 66

Rhizobia bacteria provide leguminous plants useable nitrogen through their capability to fix atmospheric nitrogen (N2) into ammonia (NH3). Specifically, rhizobia fix nitrogen in nodules, specific root structures, and receive carbohydrates from the plant in a reciprocally beneficial symbiosis. Nitrogen fixation is energetically costly to rhizobia as it uses resources that could be used towards growth and reproduction. Therefore, natural selection favors ‘cheaters’; rhizobia living in nodules that fix less nitrogen. To maintain this symbiosis, plants must favor rhizobia that fix the most nitrogen and/or use sanctions to penalize ‘cheaters’. I am investigating this relationship by isolating rhizobia and observing their interactions between each other and Pisum sativum (pea). Five bacterial strains were isolated from nodules of Lupinus sp. and P. sativum. 16S rDNA analysis identified four of the strains as Rhizobium leguminosarum and the other as R. rhizogenes. Nodulation assays showed that R. rhizogenes and one of the R. leguminosarum strains do not nodulate pea. Successful nodulating strains resulted in healthy green plants with pink nodules, however co-inoculation with nodulating and non-nodulating strains resulted in white nodules and yellow leaf coloration signifying stress. Furthermore, biofilm production was found to differ among strains of R. leguminosarum. All strains were resistant to ampicillin, and green fluorescent protein (GFP) and mCherry fluorescent markers were introduced into the bacteria. This fluorescence will be used to identify bacteria in co-inoculated pea nodules to observe occupancy patterns. This study will increase our understanding of the interactions between agriculturally applied bacterial bio-fertilizers and naturally occurring soil rhizobia.