Comparative Genomics, Siderophore Production, and Iron Scavenging Potential of Root Zone Soil Bacteria Isolated from 'Concord' Grape Vineyards

Iron (Fe) deficiency in crop production is a worldwide problem which often results in chlorosis in grapevines, particularly in calcareous soils. Siderophores secreted by microorganisms and Strategy II plants can chelate Fe and other metals in soil solution, and siderophore-Fe complexes can then be utilized by plants and microbes. Plants may also shift rhizosphere conditions to favor siderophore-producing microbes, which can increase plant available Fe. Between-row cover crops (barley, rye, wheat, wheat/vetch) were planted as living mulch to address grapevine chlorosis by enhancing soil health in two vineyards in central Washington. The objectives of the current study were to (1) enrich for siderophore-producing organisms from within the indigenous rooting zone community of 'Concord' grapevines, and (2) perform comparative genomics on putative siderophore producing organisms to assess potentially important Fe acquisition-related functional domains and protein families. A high-throughput, chrome azurol S (CAS)-based enrichment assay was used to select siderophore-producing microbes from 'Concord' grapevine root zone soil. Next-generation whole genome sequencing allowed the assembly and annotation of ten full genomes. Phylogenetic analysis revealed two distinct clades among the genomes using the 40 nearest neighbors available in the public database, all of which were of the Pseudomonas genus. Significant differences in functional domain abundances were observed between the clades including iron acquisition and metabolism of amino acids, carbon, nitrogen, phosphate, and sulfur. Diverse mechanisms of Fe uptake and siderophore production/uptake were identified in the protein families of the genomes. The sequenced organisms are likely pseudomonads which are well-suited for iron scavenging, suggesting a potential role in Fe turnover in vineyard systems.