B41F-0496
Impact of phenazine-1-carboxylic acid upon iron speciation and microbial biomass in the rhizosphere of wheat

Thursday, 17 December 2015
Poster Hall (Moscone South)
Melissa LeTourneau1, Matthew Marshall2, Michael Grant1, Patrick Freeze1, John B Cliff3, Barry Lai4, Daniel G Strawn5, Linda S Thomashow6, David M Weller6 and James B Harsh1, (1)Washington State University, Department of Crop & Soil Sciences, Pullman, WA, United States, (2)Pacific Northwest National Laboratory, Biological Sciences Division, Richland, WA, United States, (3)Pacific Northwest National Laboratory, Environmental Molecular Sciences Laboratory, Richland, WA, United States, (4)Argonne National Laboratory, Argonne, IL, United States, (5)University of Idaho, Department of Plant, Soil, & Entomological Sciences, Moscow, ID, United States, (6)Washington State University, USDA-ARS, Pullman, WA, United States
Abstract:
Phenazine-1-carboxylic acid (PCA) is a redox-active antibiotic produced by diverse bacterial taxa, and has been shown to facilitate interactions between biofilms and iron (hydr)oxides in culture systems (Wang et al. 2011, J Bacteriol 192: 365). Because rhizobacterial biofilms are a major sink for plant-derived carbon and source for soil organic matter (SOM), and Fe (hydr)oxides have reactive surfaces that influence the stability of microbial biomass and SOM, PCA-producing rhizobacteria could influence soil carbon fluxes. Large populations of Pseudomonas fluorescens strains producing PCA in concentrations up to 1 µg/g root have been observed in the rhizosphere of non-irrigated wheat fields covering 1.56 million hectares of central Washington state. This is one of the highest concentrations ever reported for a natural antibiotic in a terrestrial ecosystem (Mavrodi et al. 2012, Appl Environ Microb 78: 804).

Microscopic comparisons of PCA-producing (PCA+) and non-PCA-producing (PCA-) rhizobacterial colony morphologies, and comparisons of Fe extractions from rhizosphere soil inoculated with PCA+ and PCA- strains suggest that PCA promotes biofilm development as well as dramatic Fe transformations throughout the rhizosphere (unpublished data). In order to illustrate PCA-mediated interactions between biofilms and Fe (hydr)oxides in the rhizosphere, identify the specific Fe phases favored by PCA, and establish the ramifications for stability and distribution of microbial biomass and SOM, we have collected electron micrographs, X-ray fluorescence images, X-ray absorption near-edge spectra, and secondary-ion mass spectrometry images of wheat root sections inoculated with 15N-labelled PCA+ or PCA- rhizobacteria. These images and spectra allow us to assess the accumulation, turnover, and distribution of microbial biomass, the associations between Fe and other nutrients such as phosphorus, and the redox status and speciation of iron in the presence and absence of PCA. This information provides a starting point to model the impact of PCA upon carbon fluxes in Columbia Basin agro-ecosystems and other environments where PCA-producing bacteria are prevalent.

<< Previous Abstract | Next Abstract >>