Submitted to: Ecotoxicology and Environmental Safety
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/9/2024
Publication Date: 11/13/2024
Citation: Ketehouli, T., Goss, E., Ascunce, M.S., Martins, S.J. 2024. Metabolic and physiological effects of antibiotic-induced dysbiosis in citrus. Ecotoxicology and Environmental Safety. 287:117325. https://doi.org/10.1016/j.ecoenv.2024.117325.
DOI: https://doi.org/10.1016/j.ecoenv.2024.117325

Interpretive Summary: Antimicrobials are used in agriculture to treat microbial diseases of plants. However, nowadays, there is an increase knowledge of the beneficial role of a healthy microbiome among organisms including plants. Thus, to assess the impact of antimicrobials on plant health, studies need to evaluate their effects on both the pathogen to be treated, the whole plant microbial community as well as the plant itself. In this study, we focused in analyzing the use of two antibiotics that are being used to treat Huanglongbing (HLB) or citrus greening disease. This disease is devastating citrus worldwide and is caused by the bacterium Candidatus Liberibacter asiaticus (CLas). Two antibiotics: streptomycin (Str) and oxytetracycline (Otc) are being used to manage this disease in Florida. In this work, we assessed how these two antibiotics affected the plant physiology and beneficial bacteria. Antibiotic application negatively impacted photosynthesis and reduced particular bacterial groups. Different metabolites were affected by each antibiotic which could be related to their different mode of action. While oxytetracycline and streptomycin application could potentially combat CLas, it may also have detrimental effects on plant physiology and growth, as antibiotic application affects beneficial rhizobacteria, known to improve plant health, development, and physiology. Further plant cellular function investigations coupled with measuring long-term effects will determine the exact impacts of Str and Otc on citrus plant health and microbiome.

Technical Abstract: Citrus greening disease, caused by Candidatus Liberibacter asiaticus (CLas), poses an imminent threat to citrus output worldwide. Streptomycin (Str) and oxytetracycline (Otc) are antibiotics used to manage the disease in Florida State, but their impact on the rhizosphere ecosystem is poorly understood. This study examined the effects of Str and Otc on the physiology, rhizosphere bacterial populations, and metabolites of Citrus reticulata. After treatment of the rhizosphere with Str or Otc, physiological characteristics, including photosynthesis and CO2 flux, cultural antibiotic-resistant bacteria, bacterial community composition using high-throughput sequencing of 16S rRNA genes, and rhizosphere metabolomic patterns were assessed. Results indicated a reduction in photosynthesis with Str and Otc treatment, whereas CO2 outflow stayed constant. Both antibiotics decreased cultural numbers of microorganisms. Analysis of the microbiome showed alterations in particular bacterial groups, specifically Pseudomonas, Rhizobium, and Streptomyces, in response to the antibiotics. Further metabolomic investigations demonstrated that the top ten downregulated and upregulated metabolites between streptomycin- and oxytetracycline-treated citrus plants are entirely different, suggesting that these two antibiotics may have different plant/microbe targets or induce different stress responses. Understanding the combined impact of antibiotics on the rhizosphere metabolome and microbiome, and plant physiology is essential for creating enduring tactics to manage citrus greening while safeguarding rhizosphere ecology. This study enhances the understanding of antibiotic-driven disease management and its effects on plant photosynthesis and microbiomes.