An Pipeline for Screening and Selection of Citrus-Associated Microbiota with Potential Anti-" Liberibacter asiaticus" Properties.

Huanglongbing (HLB) is a destructive citrus disease that is lethal to all commercial citrus plants, making it the most serious citrus disease and one of the most serious plant diseases. Because of the severity of HLB and the paucity of effective control measures, we structured this study to encompass the entirety of the citrus microbiome and the chemistries associated with that microbial community. We describe the spatial niche diversity of bacteria and fungi associated with citrus roots, stems, and leaves using traditional microbial culturing integrated with culture-independent methods. Using the culturable sector of the citrus microbiome, we created a microbial repository using a high-throughput bulk culturing and microbial identification pipeline. We integrated an agar diffusion inhibition bioassay into our culturing pipeline that queried the repository for antimicrobial activity against , a culturable surrogate for the nonculturable " Liberibacter asiaticus" bacterium associated with HLB. We identified microbes with robust inhibitory activity against that include the fungi and and bacterial species of , , and Purified bioactive natural products with anti-"" activity were identified from the fungus Bioassay-guided fractionation of an organic extract of yielded the natural products cladosporols A, C, and D as the active agents against This work serves as a foundation for unraveling the complex chemistries associated with the citrus microbiome to begin to understand the functional roles of members of the microbiome, with the long-term goal of developing anti-" Liberibacter asiaticus" bioinoculants that thrive in the citrus holosystem. Globally, citrus is threatened by huanglongbing (HLB), and the lack of effective control measures is a major concern of farmers, markets, and consumers. There is compelling evidence that plant health is a function of the activities of the plant's associated microbiome. Using , a culturable surrogate for the unculturable HLB-associated bacterium " Liberibacter asiaticus," we tested the hypothesis that members of the citrus microbiome produce potential anti-" Liberibacter asiaticus" natural products with potential anti-" Liberibacter asiaticus" activity. A subset of isolates obtained from the microbiome inhibited growth in an agar diffusion inhibition assay. Further fractionation experiments linked the inhibitory activity of the fungus to the fungus-produced natural products cladosporols A, C, and D, demonstrating dose-dependent antagonism to .