Plant Associated Bacteria, so Different and so Similar: From Pathogens to Symbionts and to Biological Control Agents

A special issue of Microorganisms (ISSN 2076-2607). This special issue belongs to the section "Plant Microbe Interactions".

Deadline for manuscript submissions: closed (15 November 2021) | Viewed by 28665

Special Issue Editors


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Laboratorio di Patologia Vegetale Molecolare, Dipartimento di Scienze e Tecnologie Agrarie, Alimentari Ambientali e Forestali, Università degli Studi di Firenze, Via della Lastruccia 10, 50019 Sesto Fiorentino, Firenze, Italy
Interests: molecular plant pathology; phytopathogenic bacteria; quarantine phytopathogens; molecular epidemiology; molecular diagnostics; innovative sustainable control; auxin; MATE transporters; Pseudomonas savastanoi; Curtobacterium flaccumfacien
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Center Agriculture Food Environment C3A, University of Trento/Fondazione Edmund Mach, Trento, Italy
Interests: biological control; environmental microbiology; molecular microbiology; transcriptomics; genomics; Lysobacter; Bacillus; Pseudomonas; molecular plant pathology

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Curtin Health Innovation Research Institute, Faculty of Health Sciences, Curtin University, Perth, Australia
Interests: plant-bacteria interaction; horizontal gene transfer; bacterial evolution; integrative conjugative elements; Pseudomonas syringae pv actinidiae; molecular biology

Special Issue Information

Dear Colleagues,
 
This Special Issue will provide a collection of the most recent, and significantly advanced, research on the extensive molecular interactions that plant-associated bacteria establish with their hosts, as well as with other microorganisms. Particular attention will be given to those common or diversifying strategies, mechanisms, and molecules that bacterial plant pathogens, symbionts, and biological control agents rely on for plant colonization and to cope with plant-associated microbes and communities.
 
Information from bacterial comparative genomics, transcriptomic, and metabolomic analysis, together with functional and ecology studies, will provide innovative opportunities to unveil the molecular pathways driving the multifaceted evolution of plant-associated bacteria. At the same time, this information will also be useful to develop eco-friendly and effective plant protection strategies, increase crop yields and quality, and to safeguard the environment.
 
We look forward to providing a platform to promote the best current research on plant-associated bacteria with your contributions. Original research articles, short communications, and reviews related to the mentioned topics are welcome. Please, contact Guest editors for any information on this Special issue.

Prof. Dr. Stefania Tegli
Prof. Dr. Gerardo Puopolo
Dr. Elena Colombi
Guest Editors

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Keywords

  • Plant-associated bacteria
  • Plant pathogens, symbionts, and biocontrol agents
  • Bacterial communication
  • Bacterial secretion systems
  • Bacterial effectors
  • Quarantine bacteria
  • Genomics
  • Transcriptomics
  • Metabolomic
  • Epidemiology
  • Molecular and innovative diagnosis
  • Ecofriendly control of plant diseases

Published Papers (9 papers)

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Research

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17 pages, 4987 KiB  
Article
Priming of Resistance-Related Phenolics: A Study of Plant-Associated Bacteria and Hymenoscyphus fraxineus
by Greta Striganavičiūtė, Jonas Žiauka, Vaida Sirgedaitė-Šėžienė and Dorotėja Vaitiekūnaitė
Microorganisms 2021, 9(12), 2504; https://doi.org/10.3390/microorganisms9122504 - 2 Dec 2021
Cited by 11 | Viewed by 1771
Abstract
European ash (Fraxinus excelsior) is highly affected by the pathogenic fungus Hymenoscyphus fraxineus in all of Europe. Increases in plant’s secondary metabolite (SM) production is often linked tol enhanced resistance to stress, both biotic and abiotic. Moreover, plant-associated bacteria have been [...] Read more.
European ash (Fraxinus excelsior) is highly affected by the pathogenic fungus Hymenoscyphus fraxineus in all of Europe. Increases in plant’s secondary metabolite (SM) production is often linked tol enhanced resistance to stress, both biotic and abiotic. Moreover, plant-associated bacteria have been shown to enhance SM production in inoculated plants. Thus, our hypothesis is that bacteria may boost ash SM production, hence priming the tree’s metabolism and facilitating higher levels of resilience to H. fraxineus. We tested three different ash genotypes and used Paenibacillus sp. and Pseudomonas sp. for inoculation in vitro. Total phenol (TPC), total flavonoid (TFC) and carotenoid contents were measured, as well as the chlorophyll a/b ratio and morphometric growth parameters, in a two-stage trial, whereby seedlings were inoculated with the bacteria during the first stage and with H. fraxineus during the second stage. While the tested bacteria did not positively affect the morphometric growth parameters of ash seedlings, they had a statistically significant effect on TPC, TFC, the chlorophyll a/b ratio and carotenoid content in both stages, thus confirming our hypothesis. Specifically, in ash genotype 64, both bacteria elicited an increase in carotenoid content, TPC and TFC during both stages. Additionally, Pseudomonas sp. inoculated seedlings demonstrated an increase in phenolics after infection with the fungus in both genotypes 64 and 87. Our results indicate that next to genetic selection of the most resilient planting material for ash reforestation, plant-associated bacteria could also be used to boost ash SM production. Full article
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18 pages, 12314 KiB  
Article
Multilocus Genotyping of ‘Candidatus Phytoplasma solani’ Associated with Rubbery Taproot Disease of Sugar Beet in the Pannonian Plain
by Živko Ćurčić, Andrea Kosovac, Jelena Stepanović, Emil Rekanović, Michael Kube and Bojan Duduk
Microorganisms 2021, 9(9), 1950; https://doi.org/10.3390/microorganisms9091950 - 14 Sep 2021
Cited by 14 | Viewed by 2671
Abstract
Rubbery taproot disease of sugar beet (RTD), associated with ‘Candidatus Phytoplasma solani’, appeared in 2020 on an epidemic scale in northern Serbia and southern Slovakia, situated at opposite edges of the Pannonian Plain. In the affected locations where the disease was assessed, [...] Read more.
Rubbery taproot disease of sugar beet (RTD), associated with ‘Candidatus Phytoplasma solani’, appeared in 2020 on an epidemic scale in northern Serbia and southern Slovakia, situated at opposite edges of the Pannonian Plain. In the affected locations where the disease was assessed, symptomatic sugar beets were analysed for phytoplasma infection. Additionally, multilocus sequence analyses of ‘Ca. P. solani’ strains on epidemiologically informative marker genes (tuf, stamp and vmp1) were performed. Symptomatic sugar beets from other countries of the Pannonian Plain (Croatia, Hungary and Austria), one sample from Germany, and red beets from Serbia were included in the analyses. ‘Ca. P. solani’ was detected in sugar beet in all assessed countries, as well as in red beet. Molecular analyses revealed the high genetic variability of ‘Ca. P. solani’ with the presence of all four tuf-types (a, b1, b2 and d), 14 stamp genotypes (seven new) and five vmp1 profiles (one new). The most common multilocus genotype in Serbia, Slovakia, Croatia, and Hungary was dSTOLg (tuf-d/STOL/V2-TA). It was dominant on sites with epidemic RTD outbreaks in the Pannonian Plain and in several sugar beet fields with non-epidemic RTD occurrence suggesting the prevalence of a particular epidemiological pathway during the epidemic’s phases. Full article
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18 pages, 3949 KiB  
Article
Impact of Plant-Associated Bacteria on the In Vitro Growth and Pathogenic Resistance against Phellinus tremulae of Different Aspen (Populus) Genotypes
by Greta Striganavičiūtė, Jonas Žiauka, Vaida Sirgedaitė-Šėžienė and Dorotėja Vaitiekūnaitė
Microorganisms 2021, 9(9), 1901; https://doi.org/10.3390/microorganisms9091901 - 7 Sep 2021
Cited by 9 | Viewed by 2342
Abstract
Aspens (Populus tremula and its hybrids), economically and ecologically important fast-growing trees, are often damaged by Phellinus tremulae, a rot-causing fungus. Plant-associated bacteria can be used to increase plant growth and resistance; however, no systematic studies relating the activity of symbiotic [...] Read more.
Aspens (Populus tremula and its hybrids), economically and ecologically important fast-growing trees, are often damaged by Phellinus tremulae, a rot-causing fungus. Plant-associated bacteria can be used to increase plant growth and resistance; however, no systematic studies relating the activity of symbiotic bacteria to aspen resistance against Phellinus tremulae have been conducted so far. The present pioneer study investigated the responses of two Populus tremula and two P. tremula × P. tremuloides genotypes to in vitro inoculations with, first, either Pseudomonas sp. or Paenibacillus sp. bacteria (isolated originally from hybrid aspen tissue cultures and being most closely related to Pseudomonas oryzihabitans and Paenibacillus tundrae, respectively) and, in the subsequent stage, with Phellinus tremulae. Both morphological parameters of in vitro-grown plants and biochemical content of their leaves, including photosynthesis pigments and secondary metabolites, were analyzed. It was found that both Populus tremula × P. tremuloides genotypes, whose development in vitro was significantly damaged by Phellinus tremulae, were characterized by certain responses to the studied bacteria: decreased shoot development by both Paenibacillus sp. and Pseudomonas sp. and increased phenol content by Pseudomonas sp. In turn, these responses were lacking in both Populus tremula genotypes that showed in vitro resistance to the fungus. Moreover, these genotypes showed positive long-term growth responses to bacterial inoculation, even synergistic with the subsequent fungal inoculation. Hence, the studied bacteria were demonstrated as a potential tool for the improved in vitro propagation of fungus-resistant aspen genotypes. Full article
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14 pages, 2010 KiB  
Article
Beneficial Insects Deliver Plant Growth-Promoting Bacterial Endophytes between Tomato Plants
by Nikoletta Galambos, Stéphane Compant, Felix Wäckers, Angela Sessitsch, Gianfranco Anfora, Valerio Mazzoni, Ilaria Pertot and Michele Perazzolli
Microorganisms 2021, 9(6), 1294; https://doi.org/10.3390/microorganisms9061294 - 14 Jun 2021
Cited by 7 | Viewed by 4078
Abstract
Beneficial insects and mites, including generalist predators of the family Miridae, are widely used in biocontrol programs against many crop pests, such as whiteflies, aphids, lepidopterans and mites. Mirid predators frequently complement their carnivore diet by feeding plant sap with their piercing–sucking mouthparts. [...] Read more.
Beneficial insects and mites, including generalist predators of the family Miridae, are widely used in biocontrol programs against many crop pests, such as whiteflies, aphids, lepidopterans and mites. Mirid predators frequently complement their carnivore diet by feeding plant sap with their piercing–sucking mouthparts. This implies that mirids may act as vectors of phytopathogenic and beneficial microorganisms, such as plant growth-promoting bacterial endophytes. This work aimed at understanding the role of two beneficial mirids (Macrolophus pygmaeus and Nesidiocoris tenuis) in the acquisition and transmission of two plant growth-promoting bacteria, Paraburkholderia phytofirmans strain PsJN (PsJN) and Enterobacter sp. strain 32A (32A). Both bacterial strains were detected on the epicuticle and internal body of both mirids at the end of the mirid-mediated transmission. Moreover, both mirids were able to transmit PsJN and 32A between tomato plants and these bacterial strains could be re-isolated from tomato shoots after mirid-mediated transmission. In particular, PsJN and 32A endophytically colonised tomato plants and moved from the shoots to roots after mirid-mediated transmission. In conclusion, this study provided novel evidence for the acquisition and transmission of plant growth-promoting bacterial endophytes by beneficial mirids. Full article
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25 pages, 3582 KiB  
Article
Evaluation of Indigenous Olive Biocontrol Rhizobacteria as Protectants against Drought and Salt Stress
by Nuria Montes-Osuna, Carmen Gómez-Lama Cabanás, Antonio Valverde-Corredor, Garikoitz Legarda, Pilar Prieto and Jesús Mercado-Blanco
Microorganisms 2021, 9(6), 1209; https://doi.org/10.3390/microorganisms9061209 - 3 Jun 2021
Cited by 8 | Viewed by 3035
Abstract
Stress caused by drought and salinity may compromise growth and productivity of olive (Olea europaea L.) tree crops. Several studies have reported the use of beneficial rhizobacteria to alleviate symptoms produced by these stresses, which is attributed in some cases to the [...] Read more.
Stress caused by drought and salinity may compromise growth and productivity of olive (Olea europaea L.) tree crops. Several studies have reported the use of beneficial rhizobacteria to alleviate symptoms produced by these stresses, which is attributed in some cases to the activity of 1-aminocyclopropane-1-carboxylic acid deaminase (ACD). A collection of beneficial olive rhizobacteria was in vitro screened for ACD activity. Pseudomonas sp. PICF6 displayed this phenotype and sequencing of its genome confirmed the presence of an acdS gene. In contrast, the well-known root endophyte and biocontrol agent Pseudomonas simiae PICF7 was defective in ACD activity, even though the presence of an ACD-coding gene was earlier predicted in its genome. In this study, an unidentified deaminase was confirmed instead. Greenhouse experiments with olive ‘Picual’ plants inoculated either with PICF6 or PICF7, or co-inoculated with both strains, and subjected to drought or salt stress were carried out. Several physiological and biochemical parameters increased in stressed plants (i.e., stomatal conductance and flavonoids content), regardless of whether or not they were previously bacterized. Results showed that neither PICF6 (ACD positive) nor PICF7 (ACD negative) lessened the negative effects caused by the abiotic stresses tested, at least under our experimental conditions. Full article
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16 pages, 1028 KiB  
Article
Ecological Role of Volatile Organic Compounds Emitted by Pantoea agglomerans as Interspecies and Interkingdom Signals
by Maria Vasseur-Coronado, Anthi Vlassi, Hervé Dupré du Boulois, Rainer Schuhmacher, Alexandra Parich, Ilaria Pertot and Gerardo Puopolo
Microorganisms 2021, 9(6), 1186; https://doi.org/10.3390/microorganisms9061186 - 31 May 2021
Cited by 9 | Viewed by 3156
Abstract
Volatile organic compounds (VOCs) play an essential role in microbe–microbe and plant–microbe interactions. We investigated the interaction between two plant growth-promoting rhizobacteria, and their interaction with tomato plants. VOCs produced by Pantoea agglomerans MVC 21 modulates the release of siderophores, the solubilisation of [...] Read more.
Volatile organic compounds (VOCs) play an essential role in microbe–microbe and plant–microbe interactions. We investigated the interaction between two plant growth-promoting rhizobacteria, and their interaction with tomato plants. VOCs produced by Pantoea agglomerans MVC 21 modulates the release of siderophores, the solubilisation of phosphate and potassium by Pseudomonas (Ps.) putida MVC 17. Moreover, VOCs produced by P. agglomerans MVC 21 increased lateral root density (LRD), root and shoot dry weight of tomato seedlings. Among the VOCs released by P. agglomerans MVC 21, only dimethyl disulfide (DMDS) showed effects similar to P. agglomerans MVC 21 VOCs. Because of the effects on plants and bacterial cells, we investigated how P. agglomerans MVC 21 VOCs might influence bacteria–plant interaction. Noteworthy, VOCs produced by P. agglomerans MVC 21 boosted the ability of Ps. putida MVC 17 to increase LRD and root dry weight of tomato seedlings. These results could be explained by the positive effect of DMDS and P. agglomerans MVC 21 VOCs on acid 3-indoleacetic production in Ps. putida MVC 17. Overall, our results clearly indicated that P. agglomerans MVC 21 is able to establish a beneficial interaction with Ps. putida MVC 17 and tomato plants through the emission of DMDS. Full article
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17 pages, 788 KiB  
Article
Volatile-Mediated Inhibitory Activity of Rhizobacteria as a Result of Multiple Factors Interaction: The Case of Lysobacter capsici AZ78
by Anthi Vlassi, Andrea Nesler, Alexandra Parich, Gerardo Puopolo and Rainer Schuhmacher
Microorganisms 2020, 8(11), 1761; https://doi.org/10.3390/microorganisms8111761 - 9 Nov 2020
Cited by 8 | Viewed by 2672
Abstract
Plant beneficial rhizobacteria may antagonize soilborne plant pathogens by producing a vast array of volatile organic compounds (VOCs). The production of these compounds depends on the medium composition used for bacterial cell growth. Accordingly, Lysobacter capsici AZ78 (AZ78) grown on a protein-rich medium [...] Read more.
Plant beneficial rhizobacteria may antagonize soilborne plant pathogens by producing a vast array of volatile organic compounds (VOCs). The production of these compounds depends on the medium composition used for bacterial cell growth. Accordingly, Lysobacter capsici AZ78 (AZ78) grown on a protein-rich medium was previously found to emit volatile pyrazines with toxic activity against soilborne phypathogenic fungi and oomycetes. However, the discrepancy between the quantity of pyrazines in the gaseous phase and the minimum quantity needed to achieve inhibition of plant pathogens observed, lead us to further investigate the volatile-mediated inhibitory activity of AZ78. Here, we show that, besides VOCs, AZ78 cells produce ammonia in increased amounts when a protein-rich medium is used for bacterial growth. The production of this volatile compound caused the alkalinization of the physically separated culture medium where Rhizoctonia solani was inoculated subsequently. Results achieved in this work clearly demonstrate that VOC, ammonia and the growth medium alkalinization contribute to the overall inhibitory activity of AZ78 against R. solani. Thus, our findings suggest that the volatile-mediated inhibitory activity of rhizobacteria in protein-rich substrates can be regarded as a result of multiple factors interaction, rather than exclusively VOCs production. Full article
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13 pages, 1367 KiB  
Article
A Powerful LAMP Weapon against the Threat of the Quarantine Plant Pathogen Curtobacterium flaccumfaciens pv. flaccumfaciens
by Stefania Tegli, Carola Biancalani, Aleksandr N. Ignatov and Ebrahim Osdaghi
Microorganisms 2020, 8(11), 1705; https://doi.org/10.3390/microorganisms8111705 - 31 Oct 2020
Cited by 10 | Viewed by 3223
Abstract
Curtobacterium flaccumfaciens pv. flaccumfaciens (Cff) is a Gram-positive phytopathogenic bacterium attacking leguminous crops and causing systemic diseases such as the bacterial wilt of beans and bacterial spot of soybeans. Since the early 20th century, Cff is reported to be present in [...] Read more.
Curtobacterium flaccumfaciens pv. flaccumfaciens (Cff) is a Gram-positive phytopathogenic bacterium attacking leguminous crops and causing systemic diseases such as the bacterial wilt of beans and bacterial spot of soybeans. Since the early 20th century, Cff is reported to be present in North America, where it still causes high economic losses. Currently, Cff is an emerging plant pathogen, rapidly spreading worldwide and occurring in many bean-producing countries. Infected seeds are the main dissemination pathway for Cff, both over short and long distances. Cff remains viable in the seeds for long times, even in field conditions. According to the most recent EU legislation, Cff is included among the quarantine pests not known to occur in the Union territory, and for which the phytosanitary inspection consists mainly of the visual examination of imported bean seeds. The seedborne nature of Cff combined with the globalization of trades urgently call for the implementation of a highly specific diagnostic test for Cff, to be routinely and easily used at the official ports of entry and into the fields. This paper reports the development of a LAMP (Loop-Mediated Isothermal Amplification) specific for Cff, that allows the detection of Cff in infected seeds, both by fluorescence and visual monitoring, after 30 min of reaction and with a detection limit at around 4 fg/μL of pure Cff genomic DNA. Full article
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Review

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17 pages, 806 KiB  
Review
Beyond the Wall: Exopolysaccharides in the Biofilm Lifestyle of Pathogenic and Beneficial Plant-Associated Pseudomonas
by Zaira Heredia-Ponce, Antonio de Vicente, Francisco M. Cazorla and José Antonio Gutiérrez-Barranquero
Microorganisms 2021, 9(2), 445; https://doi.org/10.3390/microorganisms9020445 - 21 Feb 2021
Cited by 24 | Viewed by 3893
Abstract
The formation of biofilms results from a multicellular mode of growth, in which bacteria remain enwrapped by an extracellular matrix of their own production. Many different bacteria form biofilms, but among the most studied species are those that belong to the Pseudomonas genus [...] Read more.
The formation of biofilms results from a multicellular mode of growth, in which bacteria remain enwrapped by an extracellular matrix of their own production. Many different bacteria form biofilms, but among the most studied species are those that belong to the Pseudomonas genus due to the metabolic versatility, ubiquity, and ecological significance of members of this group of microorganisms. Within the Pseudomonas genus, biofilm studies have mainly focused on the opportunistic human pathogen Pseudomonas aeruginosa due to its clinical importance. The extracellular matrix of P. aeruginosa is mainly composed of exopolysaccharides, which have been shown to be important for the biofilm architecture and pathogenic features of this bacterium. Notably, some of the exopolysaccharides recurrently used by P. aeruginosa during biofilm formation, such as the alginate and polysaccharide synthesis loci (Psl) polysaccharides, are also used by pathogenic and beneficial plant-associated Pseudomonas during their interaction with plants. Interestingly, their functions are multifaceted and seem to be highly dependent on the bacterial lifestyle and genetic context of production. This paper reviews the functions and significance of the exopolysaccharides produced by plant-associated Pseudomonas, particularly the alginate, Psl, and cellulose polysaccharides, focusing on their equivalents produced in P. aeruginosa within the context of pathogenic and beneficial interactions. Full article
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