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Kennedy JP, Wood K, Pitino M, Mandadi K, Igwe DO, Shatters RG, Widmer TL, Niedz R, Heck M. A Perspective on Current Therapeutic Molecule Screening Methods Against ' Candidatus Liberibacter asiaticus', the Presumed Causative Agent of Citrus Huanglongbing. PHYTOPATHOLOGY 2023; 113:1171-1179. [PMID: 36750555 DOI: 10.1094/phyto-12-22-0455-per] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/18/2023]
Abstract
Huanglongbing (HLB), referred to as citrus greening disease, is a bacterial disease impacting citrus production worldwide and is fatal to young trees and mature trees of certain varieties. In some areas, the disease is devastating the citrus industry. A successful solution to HLB will be measured in economics: citrus growers need treatments that improve tree health, fruit production, and most importantly, economic yield. The profitability of citrus groves is the ultimate metric that truly matters when searching for solutions to HLB. Scientific approaches used in the laboratory, greenhouse, or field trials are critical to the discovery of those solutions and to estimate the likelihood of success of a treatment aimed at commercialization. Researchers and the citrus industry use a number of proxy evaluations of potential HLB solutions; understanding the strengths and limitations of each assay, as well as how best to compare different assays, is critical for decision-making to advance therapies into field trials and commercialization. This perspective aims to help the reader compare and understand the limitations of different proxy evaluation systems based on the treatment and evaluation under consideration. The researcher must determine the suitability of one or more of these metrics to identify treatments and predict the usefulness of these treatments in having an eventual impact on citrus production and HLB mitigation. As therapies advance to field trials in the next few years, a reevaluation of these metrics will be useful to guide future research efforts on strategies to mitigate HLB and vascular bacterial pathogens in other perennial crops.
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Affiliation(s)
- John Paul Kennedy
- U.S. Horticultural Research Laboratory, U.S. Department of Agriculture-Agricultural Research Service, Fort Pierce, FL 34945
| | | | | | - Kranthi Mandadi
- Department of Plant Pathology and Microbiology, Texas A&M AgriLife Research and Extension Center, Weslaco, TX 78596
- Texas A&M AgriLife Institute for Advancing Health Through Agriculture, Texas A&M AgriLife, College Station, TX 77843
| | - David O Igwe
- Plant Pathology and Plant-Microbe Biology Section, School of Integrative Plant Science, Cornell University, Ithaca, NY 14853
| | - Robert G Shatters
- U.S. Horticultural Research Laboratory, U.S. Department of Agriculture-Agricultural Research Service, Fort Pierce, FL 34945
| | - Timothy L Widmer
- U.S. Department of Agriculture-Agricultural Research Service, Beltsville, MD 20705
| | - Randall Niedz
- U.S. Horticultural Research Laboratory, U.S. Department of Agriculture-Agricultural Research Service, Fort Pierce, FL 34945
| | - Michelle Heck
- Plant Pathology and Plant-Microbe Biology Section, School of Integrative Plant Science, Cornell University, Ithaca, NY 14853
- Emerging Pests and Pathogens Research Unit, U.S. Department of Agriculture-Agricultural Research Service, Ithaca, NY 14853
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Huang Y, Zhu F, Koh J, Stanton D, Chen S, Wang N. Proteomic and bioinformatic analyses of proteins in the outer membrane and extracellular compartments and outer membrane vesicles of Candidatus Liberibacter species. Front Microbiol 2022; 13:977710. [PMID: 36225379 PMCID: PMC9548881 DOI: 10.3389/fmicb.2022.977710] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2022] [Accepted: 09/02/2022] [Indexed: 11/23/2022] Open
Abstract
Citrus Huanglongbing (HLB) is the most devastating citrus disease in the world. Candidatus Liberibacter asiaticus (Las) is the prevalent HLB pathogen, which is yet to be cultivated. A recent study demonstrates that Las does not contain pathogenicity factors that are directly responsible for HLB symptoms. Instead, Las triggers systemic and chronic immune responses, representing a pathogen-triggered immune disease. Importantly, overproduction of reactive oxygen species (ROS) causes systemic cell death of phloem tissues, thus causing HLB symptoms. Because Las resides in the phloem tissues, it is expected that phloem cell might recognize outer membrane proteins, outer membrane vesicle (OMV) proteins and extracellular proteins of Las to contribute to the immune responses. Because Las has not been cultivated, we used Liberibacter crescens (Lcr) as a surrogate to identify proteins in the OM fraction, OMV proteins and extracellular proteins by liquid chromatography with tandem mass spectrometry (LC–MS/MS). We observed OMVs of Lcr under scanning electron microscope, representing the first experimental evidence that Liberibacter can deliver proteins to the extracellular compartment. In addition, we also further analyzed LC–MS/MS data using bioinformatic tools. Our study provides valuable information regarding the biology of Ca. Liberibacter species and identifies many putative proteins that may interact with host proteins in the phloem tissues.
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Affiliation(s)
- Yixiao Huang
- Department of Plant Pathology, Citrus Research and Education Center, Institute of Food and Agricultural Sciences, University of Florida, Lake Alfred, FL, United States
| | - Fanchao Zhu
- Proteomics and Mass Spectrometry, Interdisciplinary Center for Biotechnology Research, University of Florida, Gainesville, FL, United States
| | - Jin Koh
- Proteomics and Mass Spectrometry, Interdisciplinary Center for Biotechnology Research, University of Florida, Gainesville, FL, United States
| | - Daniel Stanton
- Department of Plant Pathology, Citrus Research and Education Center, Institute of Food and Agricultural Sciences, University of Florida, Lake Alfred, FL, United States
| | - Sixue Chen
- Proteomics and Mass Spectrometry, Interdisciplinary Center for Biotechnology Research, University of Florida, Gainesville, FL, United States
| | - Nian Wang
- Citrus Research and Education Center, Department of Microbiology and Cell Science, Institute of Food and Agricultural Sciences, University of Florida, Lake Alfred, FL, United States
- *Correspondence: Nian Wang,
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Boutet E, Djerroud S, Perreault J. Small RNAs beyond Model Organisms: Have We Only Scratched the Surface? Int J Mol Sci 2022; 23:ijms23084448. [PMID: 35457265 PMCID: PMC9029176 DOI: 10.3390/ijms23084448] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2022] [Revised: 04/14/2022] [Accepted: 04/15/2022] [Indexed: 01/27/2023] Open
Abstract
Small RNAs (sRNAs) are essential regulators in the adaptation of bacteria to environmental changes and act by binding targeted mRNAs through base complementarity. Approximately 550 distinct families of sRNAs have been identified since their initial characterization in the 1980s, accelerated by the emergence of RNA-sequencing. Small RNAs are found in a wide range of bacterial phyla, but they are more prominent in highly researched model organisms compared to the rest of the sequenced bacteria. Indeed, Escherichia coli and Salmonella enterica contain the highest number of sRNAs, with 98 and 118, respectively, with Enterobacteriaceae encoding 145 distinct sRNAs, while other bacteria families have only seven sRNAs on average. Although the past years brought major advances in research on sRNAs, we have perhaps only scratched the surface, even more so considering RNA annotations trail behind gene annotations. A distinctive trend can be observed for genes, whereby their number increases with genome size, but this is not observable for RNAs, although they would be expected to follow the same trend. In this perspective, we aimed at establishing a more accurate representation of the occurrence of sRNAs in bacteria, emphasizing the potential for novel sRNA discoveries.
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Cai L, Jain M, Munoz-Bodnar A, Huguet-Tapia JC, Gabriel DW. A synthetic 'essentialome' for axenic culturing of 'Candidatus Liberibacter asiaticus'. BMC Res Notes 2022; 15:125. [PMID: 35365194 PMCID: PMC8973516 DOI: 10.1186/s13104-022-05986-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2021] [Accepted: 02/23/2022] [Indexed: 11/10/2022] Open
Abstract
OBJECTIVE 'Candidatus Liberibacter asiaticus' (CLas) is associated with the devastating citrus 'greening' disease. All attempts to achieve axenic growth and complete Koch's postulates with CLas have failed to date, at best yielding complex cocultures with very low CLas titers detectable only by PCR. Reductive genome evolution has rendered all pathogenic 'Ca. Liberibacter' spp. deficient in multiple key biosynthetic, metabolic and structural pathways that are highly unlikely to be rescued in vitro by media supplementation alone. By contrast, Liberibacter crescens (Lcr) is axenically cultured and its genome is both syntenic and highly similar to CLas. Our objective is to achieve replicative axenic growth of CLas via addition of missing culturability-related Lcr genes. RESULTS Bioinformatic analyses identified 405 unique ORFs in Lcr but missing (or truncated) in all 24 sequenced CLas strains. Site-directed mutagenesis confirmed and extended published EZ-Tn5 mutagenesis data, allowing elimination of 310 of these 405 genes as nonessential, leaving 95 experimentally validated Lcr genes as essential for CLas growth in axenic culture. Experimental conditions for conjugation of large GFP-expressing plasmids from Escherichia coli to Lcr were successfully established for the first time, providing a practical method for transfer of large groups of 'essential' Lcr genes to CLas.
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Affiliation(s)
- Lulu Cai
- Department of Plant Pathology, University of Florida, Gainesville, FL, 32611, USA
| | - Mukesh Jain
- Department of Plant Pathology, University of Florida, Gainesville, FL, 32611, USA
| | | | - Jose C Huguet-Tapia
- Department of Plant Pathology, University of Florida, Gainesville, FL, 32611, USA
| | - Dean W Gabriel
- Department of Plant Pathology, University of Florida, Gainesville, FL, 32611, USA.
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5
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Merfa MV, Naranjo E, Shantharaj D, De La Fuente L. Growth of ' Candidatus Liberibacter asiaticus' in Commercial Grapefruit Juice-Based Media Formulations Reveals Common Cell Density-Dependent Transient Behaviors. PHYTOPATHOLOGY 2022; 112:131-144. [PMID: 34340531 DOI: 10.1094/phyto-06-21-0228-fi] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
The phloem-restricted, insect-transmitted bacterium 'Candidatus Liberibacter asiaticus' (CLas) is associated with huanglongbing (HLB), the most devastating disease of citrus worldwide. The inability to culture CLas impairs the understanding of its virulence mechanisms and the development of effective management strategies to control this incurable disease. Previously, our research group used commercial grapefruit juice (GJ) to prolong the viability of CLas in vitro. In the present study, GJ was amended with a wide range of compounds and incubated under different conditions to optimize CLas growth. Remarkably, results showed that CLas growth ratios were inversely proportional to the initial inoculum concentration. This correlation is probably regulated by a cell density-dependent mechanism, because diluting samples between subcultures allowed CLas to resume growth. Moreover, strategies to reduce the cell density of CLas, such as subculturing at short intervals and incubating samples under flow conditions, allowed this bacterium to multiply and reach maximum growth as early as 3 days after inoculation, although no sustained exponential growth was observed under any tested condition. Unfortunately, cultures were only transient, because CLas lost viability over time; nevertheless, we obtained populations of about 105 genome equivalents/ml repeatedly. Finally, we established an ex vivo system to grow CLas within periwinkle calli that could be used to propagate bacterial inoculum in the lab. In this study we determined the influence of a comprehensive set of conditions and compounds on CLas growth in culture. We hope our results will help guide future efforts toward the long-sought goal of culturing CLas axenically.
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Affiliation(s)
- Marcus V Merfa
- Department of Entomology and Plant Pathology, Auburn University, Auburn, AL 36849
| | - Eber Naranjo
- Department of Entomology and Plant Pathology, Auburn University, Auburn, AL 36849
| | - Deepak Shantharaj
- Department of Entomology and Plant Pathology, Auburn University, Auburn, AL 36849
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Wang J, Haapalainen M, Nissinen AI, Pirhonen M. Dual Transcriptional Profiling of Carrot and ' Candidatus Liberibacter solanacearum' at Different Stages of Infection Suggests Complex Host-Pathogen Interaction. MOLECULAR PLANT-MICROBE INTERACTIONS : MPMI 2021; 34:1281-1297. [PMID: 34319773 DOI: 10.1094/mpmi-10-20-0274-r] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
The interactions between the phloem-limited pathogen 'Candidatus Liberibacter solanacearum' haplotype C and carrot (Daucus carota subsp. sativus) were studied at 4, 5, and 9 weeks postinoculation (wpi), by combining dual RNA-Seq results with data on bacterial colonization and observations of the plant phenotype. In the infected plants, genes involved in jasmonate biosynthesis, salicylate signaling, pathogen-associated molecular pattern- and effector-triggered immunity, and production of pathogenesis-related proteins were up-regulated. At 4 wpi, terpenoid synthesis-related genes were up-regulated, presumably as a response to the psyllid feeding, whereas at 5 and 9 wpi, genes involved in both the terpenoid and flavonoid production were down-regulated and phenylpropanoid genes were up-regulated. Chloroplast-related gene expression was down-regulated, in concordance with the observed yellowing of the infected plant leaves. Both the RNA-Seq data and electron microscopy suggested callose accumulation in the infected phloem vessels, likely to impair the transport of photosynthates, while phloem regeneration was suggested by the formation of new sieve cells and the upregulation of cell wall-related gene expression. The 'Ca. L. solanacearum' genes involved in replication, transcription, and translation were expressed at high levels at 4 and 5 wpi, whereas, at 9 wpi, the Flp pilus genes were highly expressed, suggesting adherence and reduced mobility of the bacteria. The 'Ca. L. solanacearum' genes encoding ATP and C4-dicarboxylate uptake were differentially expressed between the early and late infection stages, suggesting a change in the dependence on different host-derived energy sources. HPE1 effector and salicylate hydroxylase were expressed, presumably to suppress host cell death and salicylic acid-dependent defenses during the infection.[Formula: see text] Copyright © 2021 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.
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Affiliation(s)
- Jinhui Wang
- University of Helsinki, Department of Agricultural Sciences, P. O. Box 27, FI-00014 University of Helsinki, Finland
| | - Minna Haapalainen
- University of Helsinki, Department of Agricultural Sciences, P. O. Box 27, FI-00014 University of Helsinki, Finland
| | - Anne I Nissinen
- Natural Resources Institute Finland (Luke), Natural Resources, Tietotie 2C, FI-31600 Jokioinen, Finland
| | - Minna Pirhonen
- University of Helsinki, Department of Agricultural Sciences, P. O. Box 27, FI-00014 University of Helsinki, Finland
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Vasconcelos FNC, Li J, Pang Z, Vincent C, Wang N. The Total Population Size of ' Candidatus Liberibacter asiaticus' Inside the Phloem of Citrus Trees and the Corresponding Metabolic Burden Related to Huanglongbing Disease Development. PHYTOPATHOLOGY 2021; 111:1122-1128. [PMID: 33090080 DOI: 10.1094/phyto-09-20-0388-r] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
'Candidatus Liberibacter asiaticus' (CLas) is the predominant causal agent of citrus huanglongbing, the most devastating citrus disease worldwide. CLas colonizes phloem tissue and causes phloem dysfunction. The pathogen population size in local tissues and in the whole plant is critical for the development of disease symptoms by determining the load of pathogenicity factors and metabolic burden to the host. However, the total population size of CLas in a whole plant and the ratio of CLas to citrus cells in local tissues have not been addressed previously. The total CLas population size for 2.5-year-old 'Valencia' sweet orange on 'Kuharske' citrange rootstock trees was quantified using quantitative PCR to be approximately 1.74 × 109 cells/tree, whereas 7- and 20-year-old sweet orange trees were estimated to be 4.3 × 1010 cells/tree, and 6.0 × 1010 cells/tree, respectively. The majority of CLas cells were distributed in leaf tissues (55.58%), followed by those in branch (36.78%), feeder root (4.75%), trunk (2.39%), and structural root (0.51%) tissues. The ratios of citrus cells to CLas cells for branch, leaf, trunk, feeder root, and structural root samples were within approximately 39 to 79, 44 to 124, 153 to 1,355, 191 to 1,054, and 561 to 3,760, respectively, representing the metabolic burden of CLas in different organs. It was estimated that the ratios of phloem cells to CLas cells for branch, leaf, trunk, feeder root, and structural root samples are approximately 0.39 to 0.79, 0.44 to 1.24, 1.53 to 13.55, 1.91 to 10.54, and 5.61 to 37.60, respectively. Approximately 0.01% of the total citrus phloem volume was estimated to be occupied by CLas, explaining the difficulty to observe CLas in most tissues under transmission electron microscopy. The CLas titer inside the leaf was estimated to be approximately 1.64 × 106 cells/leaf or 9.2 × 104 cells cm-2 in leaves, approximately 104 times less than that of typical apoplastic bacterial pathogens. This study provides quantitative estimates of phloem colonization by bacterial pathogens and furthers the understanding of the biology and virulence mechanisms of CLas.
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Affiliation(s)
- Fernanda N C Vasconcelos
- Citrus Research and Education Center (CREC), Department of Microbiology and Cell Science, University of Florida, Lake Alfred, FL 33850
| | - Jinuyn Li
- Citrus Research and Education Center (CREC), Department of Microbiology and Cell Science, University of Florida, Lake Alfred, FL 33850
| | - Zhiqian Pang
- Citrus Research and Education Center (CREC), Department of Microbiology and Cell Science, University of Florida, Lake Alfred, FL 33850
| | - Christopher Vincent
- Citrus Research and Education Center (CREC), Department of Horticultural Sciences, University of Florida, Lake Alfred, FL 33850
| | - Nian Wang
- Citrus Research and Education Center (CREC), Department of Microbiology and Cell Science, University of Florida, Lake Alfred, FL 33850
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Alves MN, Cifuentes-Arenas JC, Raiol-Junior LL, Ferro JA, Peña L. Early Population Dynamics of " Candidatus Liberibacter asiaticus" in Susceptible and Resistant Genotypes After Inoculation With Infected Diaphorina citri Feeding on Young Shoots. Front Microbiol 2021; 12:683923. [PMID: 34177870 PMCID: PMC8219961 DOI: 10.3389/fmicb.2021.683923] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2021] [Accepted: 04/29/2021] [Indexed: 11/14/2022] Open
Abstract
Huanglongbing is a highly destructive citrus disease associated with "Candidatus Liberibacter asiaticus" (Las), a phloem-limited and non-culturable bacterium, naturally transmitted by the psyllid Diaphorina citri. Although diverse approaches have been used to understand the molecular mechanisms involved in the pathogen-host interaction, such approaches have focused on already infected and/or symptomatic plants, missing early events in the initial days post-inoculation. This study aimed to identify the time course of Las multiplication and whole-plant colonization immediately following inoculation by infected psyllids feeding for 2 days. Thus, the experimental approach was to track Las titers after psyllid inoculation in new shoots (NS) of Citrus × sinensis (susceptible), Murraya paniculata (partially resistant), and Bergera koenigii (fully resistant). Soon after psyllid removal, Las titers dropped until the 10-12th days in all three species. Following this, Las titers increased exponentially only in C. × sinensis and M. paniculata, indicating active bacterial multiplication. In C. × sinensis, Las reached a stationary phase at ∼5 log Las cells/g of tissue from the 40th day onward, while in M. paniculata, Las increased at a lower rate of up to ∼3 log Las cells/g of tissue between the 40th and 60th days, decreasing gradually thereafter and becoming undetectable from the 160th day onward. In B. koenigii, Las titers decreased from the start and remained undetectable. In C. × sinensis, an average of 2.6 log of Las cells/g of tissue was necessary for Las to move out of 50% of the NS in 23.6 days and to colonize the rest of the plant, causing a successful infection. Conversely, the probability of Las moving out of the NS remained below 50% in M. paniculata and zero in B. koenigii. To our knowledge, this is the first study on Las dynamics and whole-plant colonization during the earliest stages of infection. Identification of critical time-points for either successful multiplication or Las resistance may help to elucidate initial events of Las-host interactions that may be missed due to longer sampling intervals and at later stages of infection.
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Affiliation(s)
- Mônica Neli Alves
- Faculdade de Ciências Agrárias e Veterinárias (FCAV), Universidade Estadual Paulista (UNESP), Jaboticabal, Brazil
- Fundo de Defesa da Citricultura (Fundecitrus), Araraquara, Brazil
| | | | | | - Jesus Aparecido Ferro
- Faculdade de Ciências Agrárias e Veterinárias (FCAV), Universidade Estadual Paulista (UNESP), Jaboticabal, Brazil
| | - Leandro Peña
- Fundo de Defesa da Citricultura (Fundecitrus), Araraquara, Brazil
- Instituto de Biología Molecular y Celular de Plantas (IBMCP), Consejo Superior de Investigaciones Científicas (CSIC), Universidad Politécnica de Valencia (UPV), Valencia, Spain
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Naranjo E, Merfa MV, Santra S, Ozcan A, Johnson E, Cobine PA, De La Fuente L. Zinkicide Is a ZnO-Based Nanoformulation with Bactericidal Activity against Liberibacter crescens in Batch Cultures and in Microfluidic Chambers Simulating Plant Vascular Systems. Appl Environ Microbiol 2020; 86:e00788-20. [PMID: 32561578 PMCID: PMC7414956 DOI: 10.1128/aem.00788-20] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2020] [Accepted: 06/12/2020] [Indexed: 01/09/2023] Open
Abstract
Phloem-limited bacterial "Candidatus Liberibacter" species are associated with incurable plant diseases worldwide. Antimicrobial treatments for these pathogens are challenging due to the difficulty of reaching the vascular tissue they occupy at bactericidal concentrations. Here, in vitro antimicrobial mechanisms of Zinkicide TMN110 (ZnK), a nonphytotoxic zinc oxide (ZnO)-based nanoformulation, were compared to those of bulk ZnO (b-ZnO) using as a model the only culturable species of the genus, Liberibacter crescens Minimum bactericidal concentration (MBC) determination and time-kill assays showed that ZnK has a bactericidal effect against L. crescens, whereas b-ZnO is bacteriostatic. When ZnK was used at the MBC (150 ppm), its antimicrobial mechanisms included an increase in Zn solubility, generation of intracellular reactive oxygen species, lipid peroxidation, and cell membrane disruption; all of these were of greater intensity than those of b-ZnO. Inhibition of biofilms, which are important during insect vector colonization, was stronger by ZnK than by b-ZnO at concentrations between 2.5 and 10 ppm in batch cultures; however, neither ZnK nor b-ZnO removed L. crescens preformed biofilms when applied between 100 and 400 ppm. In microfluidic chambers simulating source-to-sink phloem movement, ZnK significantly outperformed b-ZnO in Zn mobilization and bactericidal activity against L. crescens planktonic cells in sink reservoirs. In microfluidic chamber assays assessing antibiofilm activity, ZnK displayed a significantly enhanced bactericidal activity against L. crescens individual attached cells as well as preformed biofilms compared to that of b-ZnO. The superior mobility and antimicrobial activity of ZnK in microenvironments make this formulation a promising product to control plant diseases caused by "Candidatus Liberibacter" species and other plant vascular pathogens.IMPORTANCE "Candidatus Liberibacter" species are associated with incurable plant diseases that have caused billions of dollars of losses for United States and world agriculture. Chemical control of these pathogens is complicated, because their life cycle combines intracellular vascular stages in plant hosts with transmission by highly mobile insect vectors. To date, "Candidatus Liberibacter" species are mostly unculturable, except for Liberibacter crescens, a member of the genus that has been used as a model for in vitro assays. Here, we evaluated the potential of Zinkicide (ZnK) as an antimicrobial against "Candidatus Liberibacter" species in batch cultures and under flow conditions, using L. crescens as a biological model. ZnK displayed bactericidal activity against L. crescens in batch cultures and showed increased mobility and bactericidal activity in microfluidic devices resembling "Candidatus Liberibacter" species natural habitats. ZnK performance observed here against L. crescens makes this compound a promising candidate to control plant diseases caused by vascular pathogens.
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Affiliation(s)
- Eber Naranjo
- Department of Entomology and Plant Pathology, Auburn University, Auburn, Alabama, USA
| | - Marcus V Merfa
- Department of Entomology and Plant Pathology, Auburn University, Auburn, Alabama, USA
| | - Swadeshmukul Santra
- NanoScience Technology Center, University of Central Florida, Orlando, Florida, USA
- Department of Chemistry, University of Central Florida, Orlando, Florida, USA
- Department of Materials Science and Engineering, University of Central Florida, Orlando, Florida, USA
- Burnett School of Biomedical Sciences, University of Central Florida, Orlando, Florida, USA
| | - Ali Ozcan
- NanoScience Technology Center, University of Central Florida, Orlando, Florida, USA
- Department of Chemistry, University of Central Florida, Orlando, Florida, USA
- Vocational School of Technical Sciences, Karamanoglu Mehmetbey University, Karaman, Turkey
| | - Evan Johnson
- Citrus Research and Education Center, University of Florida, Lake Alfred, Florida, USA
| | - Paul A Cobine
- Department of Biological Sciences, Auburn University, Auburn, Alabama, USA
| | - Leonardo De La Fuente
- Department of Entomology and Plant Pathology, Auburn University, Auburn, Alabama, USA
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10
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Blacutt A, Ginnan N, Dang T, Bodaghi S, Vidalakis G, Ruegger P, Peacock B, Viravathana P, Vieira FC, Drozd C, Jablonska B, Borneman J, McCollum G, Cordoza J, Meloch J, Berry V, Salazar LL, Maloney KN, Rolshausen PE, Roper MC. An In Vitro Pipeline for Screening and Selection of Citrus-Associated Microbiota with Potential Anti-" Candidatus Liberibacter asiaticus" Properties. Appl Environ Microbiol 2020; 86:e02883-19. [PMID: 32086307 PMCID: PMC7117939 DOI: 10.1128/aem.02883-19] [Citation(s) in RCA: 16] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2019] [Accepted: 02/11/2020] [Indexed: 12/13/2022] Open
Abstract
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 in vitro agar diffusion inhibition bioassay into our culturing pipeline that queried the repository for antimicrobial activity against Liberibacter crescens, a culturable surrogate for the nonculturable "Candidatus Liberibacter asiaticus" bacterium associated with HLB. We identified microbes with robust inhibitory activity against L. crescens that include the fungi Cladosporium cladosporioides and Epicoccum nigrum and bacterial species of Pantoea, Bacillus, and Curtobacterium Purified bioactive natural products with anti-"Ca. Liberibacter asiaticus" activity were identified from the fungus C. cladosporioides Bioassay-guided fractionation of an organic extract of C. cladosporioides yielded the natural products cladosporols A, C, and D as the active agents against L. crescens 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-"Ca Liberibacter asiaticus" bioinoculants that thrive in the citrus holosystem.IMPORTANCE 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 Liberibacter crescens, a culturable surrogate for the unculturable HLB-associated bacterium "Candidatus Liberibacter asiaticus," we tested the hypothesis that members of the citrus microbiome produce potential anti-"Ca Liberibacter asiaticus" natural products with potential anti-"Ca Liberibacter asiaticus" activity. A subset of isolates obtained from the microbiome inhibited L. crescens growth in an agar diffusion inhibition assay. Further fractionation experiments linked the inhibitory activity of the fungus Cladosporium cladosporioides to the fungus-produced natural products cladosporols A, C, and D, demonstrating dose-dependent antagonism to L. crescens.
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Affiliation(s)
- Alex Blacutt
- Department of Microbiology and Plant Pathology, University of California, Riverside, Riverside, California, USA
| | - Nichole Ginnan
- Department of Microbiology and Plant Pathology, University of California, Riverside, Riverside, California, USA
| | - Tyler Dang
- Department of Microbiology and Plant Pathology, University of California, Riverside, Riverside, California, USA
| | - Sohrab Bodaghi
- Department of Microbiology and Plant Pathology, University of California, Riverside, Riverside, California, USA
| | - Georgios Vidalakis
- Department of Microbiology and Plant Pathology, University of California, Riverside, Riverside, California, USA
| | - Paul Ruegger
- Department of Microbiology and Plant Pathology, University of California, Riverside, Riverside, California, USA
| | - Beth Peacock
- Department of Microbiology and Plant Pathology, University of California, Riverside, Riverside, California, USA
| | - Polrit Viravathana
- Department of Microbiology and Plant Pathology, University of California, Riverside, Riverside, California, USA
| | - Flavia Campos Vieira
- Department of Microbiology and Plant Pathology, University of California, Riverside, Riverside, California, USA
| | - Christopher Drozd
- Department of Microbiology and Plant Pathology, University of California, Riverside, Riverside, California, USA
| | - Barbara Jablonska
- Department of Microbiology and Plant Pathology, University of California, Riverside, Riverside, California, USA
| | - James Borneman
- Department of Microbiology and Plant Pathology, University of California, Riverside, Riverside, California, USA
| | - Greg McCollum
- U.S. Department of Agriculture, Agricultural Research Service, Fort Pierce, Florida, USA
| | | | | | - Victoria Berry
- Point Loma Nazarene University, San Diego, California, USA
| | | | | | - Philippe E Rolshausen
- Department of Botany and Plant Sciences, University of California, Riverside, Riverside, California, USA
| | - M Caroline Roper
- Department of Microbiology and Plant Pathology, University of California, Riverside, Riverside, California, USA
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