Melissa K. LeTourneau , Linda S. Thomashow , David M. Weller, and James B. Harsh

1. Transformation of soil Fe and Mn by phenazine-producing pseduomonads in the rhizosphere of dryland wheat Melissa K. LeTourneau, Linda S. Thomashow, David M. Weller, and James B. Harsh Goldschmidt, 2014

2. Iron and manganese bioavailability J. Bingham, Ohio State University, commons.wikimedia.org In aerated soils, Fe and Mn are present as insoluble Fe(III), Mn(III), and Mn(IV) oxides.

3. Plant iron nutrition Iron chlorosis in wheat • Redox processes: • -photosynthesis (ferredoxin) • -respiration (cytochromes) • -oxidative stress (catalase, SOD) • Phytosiderophores: • -Fe and Zn efficiency • -methionine precursor T. Wallace, “The Diagnosis of Mineral Deficiencies in Plants by Visual Symptoms”, hbci.com • Marschner, 1995, Mineral Nutrition of Higher Plants, 2nd ed.

4. Phenazine-producing pseudomonads Colonization frequency of phenazine-producing pseudomonads, red = fields where phenazine was isolated from wheat roots Mavrodi et al., 2012, Appl. Environ. Microbiol., 78: 804

5. Suppresses Gaeumannomycesgraminis Thomashow and Weller, 1988, J. Bacteriol., 170: 3499 Phenazine-1-carboxylic acid (PCA) Reductively dissolves Fe and Mn oxides Hernandez et al., 2004, Appl. Environ. Microbiol., 70: 921 molport.com Facilitates extracellular electron transfer in anaerobic environments such as biofilms Wang et al., 2010, J. Bacteriol., 192: 365; Wang et al., 2011, J. Bacteriol., 193: 3606; Kreamer et al., 2012, J. Bacteriol., 194: 1195

6. P. fluorescens strain 2-79 on a wheat root 5 μm

7. Our Research Objective: • Determine the impact of PCA upon Fe and Mn dynamics in the rhizosphere of wheat. Hypothesis: • PCA increases Fe and Mn availability to wheat roots.

8. Microcosm experiments

9. Microcosm experiments Bacterial inoculants: -P. fluorescensstrain 2-79 (PCA+) -PCA-deficient strain 2-79Z (PCA-) -non-inoculated controls Analysis: -poorly-crystalline Fe and Mn (hydroxylamine-hydrochloride) Chao, 1972, Soil Sci Soc Am J, 36: 764; Chao and Zhou, 1983, Soil Sci Soc Am J, 47: 225 -total Fe (citrate-dithionite) Holmgren, 1967, Soil Sci Soc Am J, 31: 210

10. Rhizosphere chemistry – Experiment 1 poor Fe: PCA- ~ PCA+ < non-inoculated

11. Experiment 1 -- Fe total Fe (ppm) poor Fe (ppm) dry dry irrigated irrigated non non PCA+ PCA+ PCA- PCA- non non PCA+ PCA+ PCA- PCA- poor Fe: PCA- ~ PCA+ < non-inoculated

12. Rhizosphere chemistry – Experiment 2 Fe: PCA- < PCA+ < non-inoculated

13. Experiment 2 -- Fe total Fe (ppm) poor Fe (ppm) dry dry irrigated irrigated non non PCA+ PCA+ PCA- PCA- non non PCA+ PCA+ PCA- PCA- Fe: PCA- < PCA+ < non-inoculated

14. Experiments 1 & 2 -- Mn Exp. 1 Mn (ppm) Exp. 2 Mn (ppm) dry dry irrigated irrigated non non PCA+ PCA+ PCA- PCA- non non PCA+ PCA+ PCA- PCA- Mn not significantly affected in this soil

15. Conclusions • While the bacterial inoculants significantly influenced Fe dynamics in the wheat rhizosphere, there is no clear evidence yet that PCA had a significant influence. • Fe(II) released by PCA may re-precipitate as secondary minerals in the rhizosphere. • Comparisons of Fe and Mn content in plant tissue are still needed to determine the impact of these strains upon Fe and Mn availability to wheat roots.

16. Acknowledgements Markus Flury, William L. Pan Daryl Stacks, Karen Hansen, Jeff Boyle, Jonathan Abarca Washington State University Crop and Soil Sciences • Otto and Doris Amen Dryland Research Endowment USDA-AFRI