Endophytes as sources of antimicrobials to control Huanglongbing (HLB)
Research by: Dr. Kateel Shetty, Florida International University, Texas A&M University; University of Florida
Article written by: Kateel G. Shetty
Article edited by: Ed Stover, Peggy Lemaux, Lukasz Stelinski
What is the research?
Endophytes are microorganisms which live inside healthy plant tissues, playing important roles in promoting plant growth and providing protection against pests and pathogens. Results from our research are focused on the microorganisms living in a specific environment of citrus plants, called the microbiome. In our case microbes are taken specifically from survivor trees. Our work showed that crude extracts of four bacteria were highly effective at killing live cells containing the HLB pathogen, CLas, in assays using ground extract of CLas-positive psyllids. The endophytic bacteria chosen were selected based on their activity against a culturable CLas substitute species, such as Liberibacter crescens. The antimicrobial activity was associated with the unconcentrated, cell-free culture extract, indicating that the unknown compound(s) is water- soluble and effective at low concentrations.
The overall goal of this project is to identify and test highly efficacious anti-CLas compounds derived from citrus endophytic bacteria that can be used to control HLB. In this USDA-NIFA-funded project we will focus on purification and characterization of the most active anti-CLas compounds from selected endophytic bacteria (Figure 1). These compounds will be pre-screened to identify the component/s that are the most active for anti-CLas activity, using the citrus CLas hairy root assay. They will be further evaluated for protective and curative effects of the purified antimicrobial compound/s against CLas under greenhouse conditions. Stakeholder outreach and engagement will be conducted through Cooperative Extension in Florida and Texas at different stages of the project.
Who is working on this project?
Kateel G. Shetty, Krish Jayachandran, and Diego Salazar Amoretti from Florida International University (FIU); Kranthi K. Mandadi from Texas A&M AgriLife Research and Extension Center; Megan M. Dewdney from UF/IFAS Citrus Research and Education Center (CREC), and Amir Rezazadeh from UF/IFAS, Ft. Pierce.
What are the challenges and opportunities?
The initial phase of the project, the extraction, fractionation, purification, and characterization of active anti-CLas compounds from individual endophytes is currently in progress. A new class of antimicrobials might require development of new chemical methods and protocols for separation and characterization of antimicrobial compounds. Combining biological compounds with different modes of actions against HLB should provide superior resistance approaches. Scaling up the production of antimicrobials and improving and optimizing plant delivery of antimicrobials may require additional time, effort, and approaches. Additional validation at the field level will be needed before the technology can be adopted for practical use. Marrone Bio Innovations, Inc., a commercial bio-pesticide company, based in California (https://marronebio.com/), has expressed interest in the project. Such public-private partnerships with commercial bio-pesticide companies can help bear the costs of the regulatory burden, commercialization, and product development needed to meet the needs of growers.
Figure 1. Process of Testing Anti-CLas Compounds