1. Presented By: Garret Morrill

2.  Many interactions exist in nature. Most are highly competitive or outright antagonistic.  How then do mutualistic relationships arise? What is the nature of them? Are they totally friendly or likewise competitive?

3. LegumeRhizobium

4.  Over 18,000 species, only surpassed by the orchid and sunflower families.  Many domesticated by humans, including soybeans, alfalfa, peanuts, all beans, etc…  Provides 1/3 of all the protein to the average human diet.  Create root nodules – the home of Nitrogen Fixation.

5.  The number of species are at least as numerous as Legumes, and most likely well over ~18,000  Free-living in soil normally, associate with legumes or Parasponia.  Contains N 2 fixation genes nif and fix. Converts Nitrogen gas (N 2 ) into Ammonia (NH 3 )  Found to have genetic histories with other bacterial species like Rickettsiaceae (Pathogen)

6.  Responsible for the majority of the world’s plant-soluable nitrogen.  Gives rise to the expensive (and delicious) structures we harvest.  A major aim of research seeks to understand this relationship better.

7. NO!

8.  Fixing N 2 is expensive – and largely unnecessary for Rhizobia. Nif and Fix genes lessen efficiency.  Specific compatibilities from HR plasmids can increase competitiveness for nodules despite lesser N 2 fixation.  Nod, Nol, Noe genes affect initial infection in a similar way, owing to the pathogen-associated history Rhizobia have.

9.  Have some mechanisms to ‘police’ Rhizobia behavior.  Compatibilities derived from immune functions (T3E response, etc…) may control entry to root.  Soybeans restrict O 2 permeability of its nodules to ‘punish’ non- productive Rhizobia.  These mechanisms may be only general though – or even rare. Many other potential mechanisms haven’t been explored yet.

10. Why does this relationship between Legumes and Rhizobia remain mutually beneficial? Metabolic/Immune regulations developed by Legumes over their evolutionary history with certain Rhizobian species have maintained N 2 fixation levels by selecting for productivity and against cheating.

11. Step 1: Obtain two genetically similar legumes with different Rhizobial strains. Measure nitrogen-fixation rates of Rhizobia with their natural hosts

12. Step 2: Switch bacterial strains between plants to produce novel lines. Grow the original combinations as well.

13. Step 3: Grow each trial separately for several generations. Continue to measure nitrogen fixation and collect genomes each generation. Bacteria

14. Step 4: Measure results over time… N 2 Fixation OriginalNovel

15. Step 4: Measure results over time… N 2 Fixation OriginalNovel

16. Step 4: Measure bacterial rate of Nitrogen Fixation over time. N 2 Fixation OriginalNovel

17.  Future studies could include testing hybrid plant response, multiple Rhizobia to compete per nodule, etc…  Would possibly lead to genetic identifications of legume mechanisms involved in ‘Nodule Policing’.  Further the research towards optimizing this most important mutualism and others like it.

18. Presented By: Garret Morrill