Project Number: 5348-22000-016-06
Project Type: Reimbursable

Start Date: Jan 01, 2011
End Date: Mar 14, 2014

Objective:
To determine (1) the impact of water availability on the structure of the microbial community associated with phenazine production in the wheat rhizosphere; (2) the molecular mechanisms involved in survival of Phz+ bacteria in the rhizosphere of dryland wheat; and (3) how wheat health is affected by presence of elevated levels of PCA in the rhizosphere.

Approach:
(1) The working hypothesis is that decreased soil moisture strongly affects the microbial rhizosphere community, leading to enrichment in Phz+ bacteria accompanied by increased production of PCA. Relationships between water potential, microbial community composition, and phenazine biosynthesis and turnover will be evaluated in greenhouse and field studies using pyrosequencing and qPCR with primers targeting 16S rDNA, phenazine and quorum-sensing (QS) genes, as well as reporter strains and HPLC-mass spectrometry. (2) Our working hypothesis is that Phz+ bacteria are uniquely adapted to colonize the plant rhizosphere under conditions of water stress due to their ability to resist desiccation via formation of robust biofilms. A draft genomic sequence of a Phz+ reference strain will be generated by pyrosequencing and used (i) to study the involvement of selected gene systems (QS circuits, polysaccharides, cyclic lipopeptides) in biofilm formation and resistance to desiccation; and (ii) to construct reporter strains for the analysis of gene expression in vitro and in situ in relation to soil moisture, root exudate constituents, and cross-communicating members of the rhizosphere microbial community. (3) The working hypothesis is that PCA affects plant gene expression and contributes to mineral reductive processes that act on rhizosphere Fe and Mn as a function of soil moisture. The AffymetrixTM Gene Chip will be used to assess the impact of PCA or Phz+ strains and isogenic Phz- mutants on wheat root gene expression under normal and water-stressed conditions. PCA and bacteria will also be evaluated for reductive dissolution of Fe and Mn in bulk soils and in the rhizosphere of seedlings maintained under dryland or irrigated conditions by standard colorimetric assays or by ICP-MS. Similar methods will be used to assess Fe concentrations in the tissues of field- and greenhouse-grown plants treated by Phz+ and Phz- bacteria. Potential impact and expected outcomes: The proposed studies will provide insight into the impact of soil moisture on the rhizosphere microbial community structure of an economically important crop and the capacity of this community to produce a biologically active metabolite. Documents Reimbursable AFRI Grant. (Award number 2011-67019-30212.) Log 42904.