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Rolli E, Ghitti E, Mapelli F, Borin S. Polychlorinated biphenyls modify Arabidopsis root exudation pattern to accommodate degrading bacteria, showing strain and functional trait specificity. FRONTIERS IN PLANT SCIENCE 2024; 15:1429096. [PMID: 39036359 PMCID: PMC11258928 DOI: 10.3389/fpls.2024.1429096] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 05/07/2024] [Accepted: 06/13/2024] [Indexed: 07/23/2024]
Abstract
Introduction The importance of plant rhizodeposition to sustain microbial growth and induce xenobiotic degradation in polluted environments is increasingly recognized. Methods Here the "cry-for-help" hypothesis, consisting in root chemistry remodeling upon stress, was investigated in the presence of polychlorinated biphenyls (PCBs), highly recalcitrant and phytotoxic compounds, highlighting its role in reshaping the nutritional and signaling features of the root niche to accommodate PCB-degrading microorganisms. Results Arabidopsis exposure to 70 µM PCB-18 triggered plant-detrimental effects, stress-related traits, and PCB-responsive gene expression, reproducing PCB phytotoxicity. The root exudates of plantlets exposed for 2 days to the pollutant were collected and characterized through untargeted metabolomics analysis by liquid chromatography-mass spectrometry. Principal component analysis disclosed a different root exudation fingerprint in PCB-18-exposed plants, potentially contributing to the "cry-for-help" event. To investigate this aspect, the five compounds identified in the exudate metabolomic analysis (i.e., scopoletin, N-hydroxyethyl-β-alanine, hypoxanthine, L-arginyl-L-valine, and L-seryl-L-phenylalanine) were assayed for their influence on the physiology and functionality of the PCB-degrading strains Pseudomonas alcaliphila JAB1, Paraburkholderia xenovorans LB400, and Acinetobacter calcoaceticus P320. Scopoletin, whose relative abundance decreased in PCB-18-stressed plant exudates, hampered the growth and proliferation of strains JAB1 and P320, presumably due to its antimicrobial activity, and reduced the beneficial effect of Acinetobacter P320, which showed a higher degree of growth promotion in the scopoletin-depleted mutant f6'h1 compared to Arabidopsis WT plants exposed to PCB. Nevertheless, scopoletin induced the expression of the bph catabolic operon in strains JAB1 and LB400. The primary metabolites hypoxanthine, L-arginyl-L-valine, and L-seryl-L-phenylalanine, which increased in relative abundance upon PCB-18 stress, were preferentially used as nutrients and growth-stimulating factors by the three degrading strains and showed a variable ability to affect rhizocompetence traits like motility and biofilm formation. Discussion These findings expand the knowledge on PCB-triggered "cry-for-help" and its role in steering the PCB-degrading microbiome to boost the holobiont fitness in polluted environments.
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Affiliation(s)
| | | | | | - Sara Borin
- Department of Food, Environmental and Nutritional Sciences (DeFENS), University of Milan, Milan, Italy
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Ghitti E, Rolli E, Vergani L, Borin S. Flavonoids influence key rhizocompetence traits for early root colonization and PCB degradation potential of Paraburkholderia xenovorans LB400. FRONTIERS IN PLANT SCIENCE 2024; 15:1325048. [PMID: 38371405 PMCID: PMC10869545 DOI: 10.3389/fpls.2024.1325048] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 10/20/2023] [Accepted: 01/15/2024] [Indexed: 02/20/2024]
Abstract
Introduction Flavonoids are among the main plant root exudation components, and, in addition to their role in symbiosis, they can broadly affect the functionality of plant-associated microbes: in polluted environments, for instance, flavonoids can induce the expression of the enzymatic degradative machinery to clean-up soils from xenobiotics like polychlorinated biphenyls (PCBs). However, their involvement in root community recruitment and assembly involving non-symbiotic beneficial interactions remains understudied and may be crucial to sustain the holobiont fitness under PCB stress. Methods By using a set of model pure flavonoid molecules and a natural blend of root exudates (REs) with altered flavonoid composition produced by Arabidopsis mutant lines affected in flavonoid biosynthesis and abundance (null mutant tt4, flavonoid aglycones hyperproducer tt8, and flavonoid conjugates hyperaccumulator ttg), we investigated flavonoid contribution in stimulating rhizocompetence traits and the catabolic potential of the model bacterial strain for PCB degradation Paraburkholderia xenovorans LB400. Results Flavonoids influenced the traits involved in bacterial recruitment in the rhizoplane by improving chemotaxis and motility responses, by increasing biofilm formation and by promoting the growth and activation of the PCB-degradative pathway of strain LB400, being thus potentially exploited as carbon sources, stimulating factors and chemoattractant molecules. Indeed, early rhizoplane colonization was favored in plantlets of the tt8 Arabidopsis mutant and reduced in the ttg line. Bacterial growth was promoted by the REs of mutant lines tt4 and tt8 under control conditions and reduced upon PCB-18 stress, showing no significant differences compared with the WT and ttg, indicating that unidentified plant metabolites could be involved. PCB stress presumably altered the Arabidopsis root exudation profile, although a sudden "cry-for-help" response to recruit strain LB400 was excluded and flavonoids appeared not to be the main determinants. In the in vitro plant-microbe interaction assays, plant growth promotion and PCB resistance promoted by strain LB400 seemed to act through flavonoid-independent mechanisms without altering bacterial colonization efficiency and root adhesion pattern. Discussions This study further contributes to elucidate the vast array of functions provided by flavonoids in orchestrating the early events of PCB-degrading strain LB400 recruitment in the rhizosphere and to support the holobiont fitness by stimulating the catabolic machinery involved in xenobiotics decomposition and removal.
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Affiliation(s)
| | - Eleonora Rolli
- Department of Food, Environmental and Nutritional Sciences (DeFENS), University of Milan, Milan, Italy
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Suman J, Sredlova K, Fraraccio S, Jerabkova M, Strejcek M, Kabickova H, Cajthaml T, Uhlik O. Transformation of hydroxylated polychlorinated biphenyls by bacterial 2-hydroxybiphenyl 3-monooxygenase. CHEMOSPHERE 2024; 349:140909. [PMID: 38070605 DOI: 10.1016/j.chemosphere.2023.140909] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/06/2023] [Revised: 08/18/2023] [Accepted: 12/04/2023] [Indexed: 12/17/2023]
Abstract
Monohydroxylated PCBs (OH-PCBs) are an (eco)toxicologically significant group of compounds, as they arise from the oxidation of polychlorinated biphenyls (PCBs) and, at the same time, may exert even more severe toxic effects than their parent PCB molecules. Despite having been widely detected in environmental samples, plants, and animals, information on the fate of OH-PCBs in the environment is scarce, including on the enzymatic machinery behind their degradation. To date, only a few bacterial taxa capable of OH-PCB transformation have been reported. In this study, we aimed to obtain a deeper insight into the transformation of OH-PCBs in soil bacteria and isolated a Pseudomonas sp. strain P1B16 based on its ability to use o-phenylphenol (2-PP) which, when exposed to the Delor 103-derived OH-PCB mixture, depleted a wide spectrum of mono-, di, and trichlorinated OH-PCBs. In the P1B16 genome, a region designated as hbp was identified, which bears a set of putative genes involved in the transformation of OH-PCBs, namely hbpA encoding for a putative flavin-dependent 2-hydroxybiphenyl monooxygenase, hbpC (2,3-dihydroxybiphenyl-1,2-dioxygenase), hbpD (2-hydroxy-6-oxo-6-phenylhexa-2,4-dienoate hydrolase), and the transcriptional activator-encoding gene hbpR. The hbpA coding sequence was heterologously expressed, purified, and its substrate specificity was investigated towards the Delor 103-derived OH-PCB mixture, individual OH-PCBs, and multiple (chlorinated) phenolics. Apart from 2-PP and 2-chlorophenol, HbpA was also demonstrated to transform a range of OH-PCBs, including a 3-hydroxy-2,2',4',5,5'-pentachlorobiphenyl. Importantly, this is the first direct evidence of HbpA homologs being involved in the degradation of OH-PCBs. Moreover, using a P1B16-based biosensor strain, the specific induction of hbp genes by 2-PP, 3-phenylphenol, 4-phenylphenol, and the OH-PCB mixture was demonstrated. This study provides direct evidence on the specific enzymatic machinery responsible for the transformation of OH-PCBs in bacteria, with many implications in ecotoxicology, environmental restoration, and microbial ecology in habitats burdened with PCB contamination.
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Affiliation(s)
- Jachym Suman
- Department of Biochemistry and Microbiology, Faculty of Food and Biochemical Technology, University of Chemistry and Technology, Technicka 3, 162 08, Prague, Czech Republic.
| | - Kamila Sredlova
- Institute for Environmental Studies, Faculty of Science, Charles University, Benatska 2, 128 01, Prague 2, Czech Republic; Institute of Microbiology of the Czech Academy of Sciences, Videnska 1083, 142 00, Prague, Czech Republic
| | - Serena Fraraccio
- Department of Biochemistry and Microbiology, Faculty of Food and Biochemical Technology, University of Chemistry and Technology, Technicka 3, 162 08, Prague, Czech Republic
| | - Martina Jerabkova
- Department of Biochemistry and Microbiology, Faculty of Food and Biochemical Technology, University of Chemistry and Technology, Technicka 3, 162 08, Prague, Czech Republic
| | - Michal Strejcek
- Department of Biochemistry and Microbiology, Faculty of Food and Biochemical Technology, University of Chemistry and Technology, Technicka 3, 162 08, Prague, Czech Republic
| | - Hana Kabickova
- Military Health Institute, Ministry of Defence of the Czech Republic, U Vojenske Nemocnice 1200, 169 02, Prague, Czech Republic
| | - Tomas Cajthaml
- Institute for Environmental Studies, Faculty of Science, Charles University, Benatska 2, 128 01, Prague 2, Czech Republic; Institute of Microbiology of the Czech Academy of Sciences, Videnska 1083, 142 00, Prague, Czech Republic
| | - Ondrej Uhlik
- Department of Biochemistry and Microbiology, Faculty of Food and Biochemical Technology, University of Chemistry and Technology, Technicka 3, 162 08, Prague, Czech Republic.
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Fujihara H, Hirose J, Suenaga H. Evolution of genetic architecture and gene regulation in biphenyl/PCB-degrading bacteria. Front Microbiol 2023; 14:1168246. [PMID: 37350784 PMCID: PMC10282184 DOI: 10.3389/fmicb.2023.1168246] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2023] [Accepted: 05/16/2023] [Indexed: 06/24/2023] Open
Abstract
A variety of bacteria in the environment can utilize xenobiotic compounds as a source of carbon and energy. The bacterial strains degrading xenobiotics are suitable models to investigate the adaptation and evolutionary processes of bacteria because they appear to have emerged relatively soon after the release of these compounds into the natural environment. Analyses of bacterial genome sequences indicate that horizontal gene transfer (HGT) is the most important contributor to the bacterial evolution of genetic architecture. Further, host bacteria that can use energy effectively by controlling the expression of organized gene clusters involved in xenobiotic degradation will have a survival advantage in harsh xenobiotic-rich environments. In this review, we summarize the current understanding of evolutionary mechanisms operative in bacteria, with a focus on biphenyl/PCB-degrading bacteria. We then discuss metagenomic approaches that are useful for such investigation.
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Affiliation(s)
- Hidehiko Fujihara
- Department of Food and Fermentation Sciences, Faculty of Food and Nutrition Sciences, Beppu University, Beppu, Japan
| | - Jun Hirose
- Department of Applied Chemistry, Faculty of Engineering, University of Miyazaki, Miyazaki, Japan
| | - Hikaru Suenaga
- Cellular and Molecular Biotechnology Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Tokyo, Japan
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Ghitti E, Rolli E, Crotti E, Borin S. Flavonoids Are Intra- and Inter-Kingdom Modulator Signals. Microorganisms 2022; 10:microorganisms10122479. [PMID: 36557733 PMCID: PMC9781135 DOI: 10.3390/microorganisms10122479] [Citation(s) in RCA: 8] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2022] [Revised: 12/07/2022] [Accepted: 12/13/2022] [Indexed: 12/23/2022] Open
Abstract
Flavonoids are a broad class of secondary metabolites with multifaceted functionalities for plant homeostasis and are involved in facing both biotic and abiotic stresses to sustain plant growth and health. Furthermore, they were discovered as mediators of plant networking with the surrounding environment, showing a surprising ability to perform as signaling compounds for a multitrophic inter-kingdom level of communication that influences the plant host at the phytobiome scale. Flavonoids orchestrate plant-neighboring plant allelopathic interactions, recruit beneficial bacteria and mycorrhizal fungi, counteract pathogen outbreak, influence soil microbiome and affect plant physiology to improve its resilience to fluctuating environmental conditions. This review focuses on the diversified spectrum of flavonoid functions in plants under a variety of stresses in the modulation of plant morphogenesis in response to environmental clues, as well as their role as inter-kingdom signaling molecules with micro- and macroorganisms. Regarding the latter, the review addresses flavonoids as key phytochemicals in the human diet, considering their abundance in fruits and edible plants. Recent evidence highlights their role as nutraceuticals, probiotics and as promising new drugs for the treatment of several pathologies.
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Suman J, Strejcek M, Zubrova A, Capek J, Wald J, Michalikova K, Hradilova M, Sredlova K, Semerad J, Cajthaml T, Uhlik O. Predominant Biphenyl Dioxygenase From Legacy Polychlorinated Biphenyl (PCB)-Contaminated Soil Is a Part of Unusual Gene Cluster and Transforms Flavone and Flavanone. Front Microbiol 2021; 12:644708. [PMID: 34721309 PMCID: PMC8552027 DOI: 10.3389/fmicb.2021.644708] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2020] [Accepted: 09/20/2021] [Indexed: 11/13/2022] Open
Abstract
In this study, the diversity of bphA genes was assessed in a 13C-enriched metagenome upon stable isotope probing (SIP) of microbial populations in legacy PCB-contaminated soil with 13C-biphenyl (BP). In total, 13 bphA sequence variants (SVs) were identified in the final amplicon dataset. Of these, one SV comprised 59% of all sequences, and when it was translated into a protein sequence, it exhibited 87, 77.4, and 76.7% identity to its homologs from Pseudomonas furukawaii KF707, Cupriavidus sp. WS, and Pseudomonas alcaliphila B-367, respectively. This same BphA sequence also contained unusual amino acid residues, Alanine, Valine, and Serine in region III, which had been reported to be crucial for the substrate specificity of the corresponding biphenyl dioxygenase (BPDO), and was accordingly designated BphA_AVS. The DNA locus of 18 kbp containing the BphA_AVS-coding sequence retrieved from the metagenome was comprised of 16 ORFs and was most likely borne by Paraburkholderia sp. The BPDO corresponding to bphAE_AVS was cloned and heterologously expressed in E. coli, and its substrate specificity toward PCBs and a spectrum of flavonoids was assessed. Although depleting a rather narrow spectrum of PCB congeners, the efficient transformation of flavone and flavanone was demonstrated through dihydroxylation of the B-ring of the molecules. The homology-based functional assignment of the putative proteins encoded by the rest of ORFs in the AVS region suggests their potential involvement in the transformation of aromatic compounds, such as flavonoids. In conclusion, this study contributes to the body of information on the involvement of soil-borne BPDOs in the metabolism of flavonoid compounds, and our paper provides a more advanced context for understanding the interactions between plants, microbes and anthropogenic compounds in the soil.
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Affiliation(s)
- Jachym Suman
- Department of Biochemistry and Microbiology, Faculty of Food and Biochemical Technology, University of Chemistry and Technology, Prague, Czechia
| | - Michal Strejcek
- Department of Biochemistry and Microbiology, Faculty of Food and Biochemical Technology, University of Chemistry and Technology, Prague, Czechia
| | - Andrea Zubrova
- Department of Biochemistry and Microbiology, Faculty of Food and Biochemical Technology, University of Chemistry and Technology, Prague, Czechia
| | - Jan Capek
- Department of Biochemistry and Microbiology, Faculty of Food and Biochemical Technology, University of Chemistry and Technology, Prague, Czechia
| | - Jiri Wald
- Department of Biochemistry and Microbiology, Faculty of Food and Biochemical Technology, University of Chemistry and Technology, Prague, Czechia
| | - Klara Michalikova
- Institute of Microbiology, Academy of Sciences of the Czech Republic, Prague, Czechia
| | - Miluse Hradilova
- Institute of Molecular Genetics of the Czech Academy of Sciences, Prague, Czechia
| | - Kamila Sredlova
- Institute of Microbiology, Academy of Sciences of the Czech Republic, Prague, Czechia
| | - Jaroslav Semerad
- Institute of Microbiology, Academy of Sciences of the Czech Republic, Prague, Czechia.,Faculty of Science, Institute for Environmental Studies, Charles University, Prague, Czechia
| | - Tomas Cajthaml
- Institute of Microbiology, Academy of Sciences of the Czech Republic, Prague, Czechia.,Faculty of Science, Institute for Environmental Studies, Charles University, Prague, Czechia
| | - Ondrej Uhlik
- Department of Biochemistry and Microbiology, Faculty of Food and Biochemical Technology, University of Chemistry and Technology, Prague, Czechia
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