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Ganusova EE, Russell MH, Patel S, Seats T, Alexandre G. An Azospirillum brasilense chemoreceptor that mediates nitrate chemotaxis has conditional roles in the colonization of plant roots. Appl Environ Microbiol 2024; 90:e0076024. [PMID: 38775579 PMCID: PMC11218637 DOI: 10.1128/aem.00760-24] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2024] [Accepted: 04/26/2024] [Indexed: 06/19/2024] Open
Abstract
Motile plant-associated bacteria use chemotaxis and dedicated chemoreceptors to navigate gradients in their surroundings and to colonize host plant surfaces. Here, we characterize a chemoreceptor that we named Tlp2 in the soil alphaproteobacterium Azospirillum brasilense. We show that the Tlp2 ligand-binding domain is related to the 4-helix bundle family and is conserved in chemoreceptors found in the genomes of many soil- and sediment-dwelling alphaproteobacteria. The promoter of tlp2 is regulated in an NtrC- and RpoN-dependent manner and is most upregulated under conditions of nitrogen fixation or in the presence of nitrate. Using fluorescently tagged Tlp2 (Tlp2-YFP), we show that this chemoreceptor is present in low abundance in chemotaxis-signaling clusters and is prone to degradation. We also obtained evidence that the presence of ammonium rapidly disrupts Tlp2-YFP localization. Behavioral experiments using a strain lacking Tlp2 and variants of Tlp2 lacking conserved arginine residues suggest that Tlp2 mediates chemotaxis in gradients of nitrate and nitrite, with the R159 residue being essential for Tlp2 function. We also provide evidence that Tlp2 is essential for root surface colonization of some plants (teff, red clover, and cowpea) but not others (wheat, sorghum, alfalfa, and pea). These results highlight the selective role of nitrate sensing and chemotaxis in plant root surface colonization and illustrate the relative contribution of chemoreceptors to chemotaxis and root surface colonization.IMPORTANCEBacterial chemotaxis mediates host-microbe associations, including the association of beneficial bacteria with the roots of host plants. Dedicated chemoreceptors specify sensory preferences during chemotaxis. Here, we show that a chemoreceptor mediating chemotaxis to nitrate is important in the beneficial soil bacterium colonization of some but not all plant hosts tested. Nitrate is the preferred nitrogen source for plant nutrition, and plants sense and tightly control nitrate transport, resulting in varying nitrate uptake rates depending on the plant and its physiological state. Nitrate is thus a limiting nutrient in the rhizosphere. Chemotaxis and dedicated chemoreceptors for nitrate likely provide motile bacteria with a competitive advantage to access this nutrient in the rhizosphere.
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Affiliation(s)
- Elena E. Ganusova
- Biochemistry and Cellular and Molecular Biology Department, University of Tennessee, Knoxville, Tennessee, USA
| | - Matthew H. Russell
- Biochemistry and Cellular and Molecular Biology Department, University of Tennessee, Knoxville, Tennessee, USA
| | - Siddhi Patel
- Biochemistry and Cellular and Molecular Biology Department, University of Tennessee, Knoxville, Tennessee, USA
| | - Terry Seats
- Biochemistry and Cellular and Molecular Biology Department, University of Tennessee, Knoxville, Tennessee, USA
| | - Gladys Alexandre
- Biochemistry and Cellular and Molecular Biology Department, University of Tennessee, Knoxville, Tennessee, USA
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Pacheco-Moreno A, Bollmann-Giolai A, Chandra G, Brett P, Davies J, Thornton O, Poole P, Ramachandran V, Brown JKM, Nicholson P, Ridout C, DeVos S, Malone JG. The genotype of barley cultivars influences multiple aspects of their associated microbiota via differential root exudate secretion. PLoS Biol 2024; 22:e3002232. [PMID: 38662644 PMCID: PMC11045101 DOI: 10.1371/journal.pbio.3002232] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2023] [Accepted: 03/19/2024] [Indexed: 04/28/2024] Open
Abstract
Plant-associated microbes play vital roles in promoting plant growth and health, with plants secreting root exudates into the rhizosphere to attract beneficial microbes. Exudate composition defines the nature of microbial recruitment, with different plant species attracting distinct microbiota to enable optimal adaptation to the soil environment. To more closely examine the relationship between plant genotype and microbial recruitment, we analysed the rhizosphere microbiomes of landrace (Chevallier) and modern (NFC Tipple) barley (Hordeum vulgare) cultivars. Distinct differences were observed between the plant-associated microbiomes of the 2 cultivars, with the plant-growth promoting rhizobacterial genus Pseudomonas substantially more abundant in the Tipple rhizosphere. Striking differences were also observed between the phenotypes of recruited Pseudomonas populations, alongside distinct genotypic clustering by cultivar. Cultivar-driven Pseudomonas selection was driven by root exudate composition, with the greater abundance of hexose sugars secreted from Tipple roots attracting microbes better adapted to growth on these metabolites and vice versa. Cultivar-driven selection also operates at the molecular level, with both gene expression and the abundance of ecologically relevant loci differing between Tipple and Chevallier Pseudomonas isolates. Finally, cultivar-driven selection is important for plant health, with both cultivars showing a distinct preference for microbes selected by their genetic siblings in rhizosphere transplantation assays.
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Affiliation(s)
- Alba Pacheco-Moreno
- John Innes Centre, Norwich Research Park, Colney Lane, Norwich, United Kingdom
| | | | - Govind Chandra
- John Innes Centre, Norwich Research Park, Colney Lane, Norwich, United Kingdom
| | - Paul Brett
- John Innes Centre, Norwich Research Park, Colney Lane, Norwich, United Kingdom
| | - Jack Davies
- John Innes Centre, Norwich Research Park, Colney Lane, Norwich, United Kingdom
| | - Owen Thornton
- John Innes Centre, Norwich Research Park, Colney Lane, Norwich, United Kingdom
| | - Philip Poole
- Department of Biology, University of Oxford, South Parks Road, Oxford, United Kingdom
| | - Vinoy Ramachandran
- Department of Biology, University of Oxford, South Parks Road, Oxford, United Kingdom
| | - James K. M. Brown
- John Innes Centre, Norwich Research Park, Colney Lane, Norwich, United Kingdom
| | - Paul Nicholson
- John Innes Centre, Norwich Research Park, Colney Lane, Norwich, United Kingdom
| | - Chris Ridout
- John Innes Centre, Norwich Research Park, Colney Lane, Norwich, United Kingdom
- New Heritage Barley, Norwich Research Park, Norwich, United Kingdom
| | - Sarah DeVos
- John Innes Centre, Norwich Research Park, Colney Lane, Norwich, United Kingdom
- New Heritage Barley, Norwich Research Park, Norwich, United Kingdom
| | - Jacob G. Malone
- John Innes Centre, Norwich Research Park, Colney Lane, Norwich, United Kingdom
- School of Biological Sciences, University of East Anglia, Norwich, United Kingdom
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Ganusova EE, Rost M, Aksenova A, Abdulhussein M, Holden A, Alexandre G. Azospirillum brasilense AerC and Tlp4b Cytoplasmic Chemoreceptors Are Promiscuous and Interact with the Two Membrane-Bound Chemotaxis Signaling Clusters Mediating Chemotaxis Responses. J Bacteriol 2023; 205:e0048422. [PMID: 37255486 PMCID: PMC10294658 DOI: 10.1128/jb.00484-22] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2022] [Accepted: 05/08/2023] [Indexed: 06/01/2023] Open
Abstract
Chemotaxis in Bacteria and Archaea depends on the presence of hexagonal polar arrays composed of membrane-bound chemoreceptors that interact with rings of baseplate signaling proteins. In the alphaproteobacterium Azospirillum brasilense, chemotaxis is controlled by two chemotaxis signaling systems (Che1 and Che4) that mix at the baseplates of two spatially distinct membrane-bound chemoreceptor arrays. The subcellular localization and organization of transmembrane chemoreceptors in chemotaxis signaling clusters have been well characterized but those of soluble chemoreceptors remain relatively underexplored. By combining mutagenesis, microscopy, and biochemical assays, we show that the cytoplasmic chemoreceptors AerC and Tlp4b function in chemotaxis and localize to and interact with membrane-bound chemoreceptors and chemotaxis signaling proteins from both polar arrays, indicating that soluble chemoreceptors are promiscuous. The interactions of AerC and Tlp4b with polar chemotaxis signaling clusters are not equivalent and suggest distinct functions. Tlp4b, but not AerC, modulates the abundance of chemoreceptors within the signaling clusters through an unknown mechanism. The AerC chemoreceptor, but not Tlp4b, is able to traffic in and out of chemotaxis signaling clusters depending on its level of expression. We also identify a role of the chemoreceptor composition of chemotaxis signaling clusters in regulating their polar subcellular organization. The organization of chemotaxis signaling proteins as large membrane-bound arrays underlies chemotaxis sensitivity. Our findings suggest that the composition of chemoreceptors may fine-tune chemotaxis signaling not only through their chemosensory specificity but also through their role in the organization of polar chemotaxis signaling clusters. IMPORTANCE Cytoplasmic chemoreceptors represent about 14% of all chemoreceptors encoded in bacterial and archaeal genomes, but little is known about how they interact with and function in large polar assemblies of membrane-bound chemotaxis signaling clusters. Here, we show that two soluble chemoreceptors with a role in chemotaxis are promiscuous and interact with two distinct membrane-bound chemotaxis signaling clusters that control all chemotaxis responses in Azospirillum brasilense. We also found that any change in the chemoreceptor composition of chemotaxis signaling clusters alters their polar organization, suggesting a dynamic interplay between the sensory specificity of chemotaxis signaling clusters and their polar membrane organization.
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Affiliation(s)
- Elena E. Ganusova
- Department of Biochemistry and Cellular and Molecular Biology, University of Tennessee, Knoxville, Tennessee, USA
| | - Madison Rost
- Department of Biochemistry and Cellular and Molecular Biology, University of Tennessee, Knoxville, Tennessee, USA
| | - Anastasia Aksenova
- Department of Biochemistry and Cellular and Molecular Biology, University of Tennessee, Knoxville, Tennessee, USA
| | - Mustafa Abdulhussein
- Department of Biochemistry and Cellular and Molecular Biology, University of Tennessee, Knoxville, Tennessee, USA
| | - Alisha Holden
- Department of Biochemistry and Cellular and Molecular Biology, University of Tennessee, Knoxville, Tennessee, USA
| | - Gladys Alexandre
- Department of Biochemistry and Cellular and Molecular Biology, University of Tennessee, Knoxville, Tennessee, USA
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4
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The GGDEF-EAL protein CdgB from Azospirillum baldaniorum Sp245, is a dual function enzyme with potential polar localization. PLoS One 2022; 17:e0278036. [PMID: 36417483 PMCID: PMC9683572 DOI: 10.1371/journal.pone.0278036] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2022] [Accepted: 11/08/2022] [Indexed: 11/27/2022] Open
Abstract
Azospirillum baldaniorum Sp245, a plant growth-promoting rhizobacterium, can form biofilms through a process controlled by the second messenger cyclic diguanylate monophosphate (c-di-GMP). A. baldaniorum has a variety of proteins potentially involved in controlling the turnover of c-di-GMP many of which are coupled to sensory domains that could be involved in establishing a mutualistic relationship with the host. Here, we present in silico analysis and experimental characterization of the function of CdgB (AZOBR_p410089), a predicted MHYT-PAS-GGDEF-EAL multidomain protein from A. baldaniorum Sp245. When overproduced, CdgB behaves predominantly as a c-di-GMP phosphodiesterase (PDE) in A. baldaniorum Sp245. It inhibits biofilm formation and extracellular polymeric substances production and promotes swimming motility. However, a CdgB variant with a degenerate PDE domain behaves as diguanylate cyclase (DGC). This strongly suggest that CdgB is capable of dual activity. Variants with alterations in the DGC domain and the MHYT domain negatively affects extracellular polymeric substances production and induction of swimming motility. Surprisingly, we observed that overproduction of CdgB results in increased c-di-GMP accumulation in the heterologous host Escherichia coli, suggesting under certain conditions, the WT CdgB variant can behave predominantly as a DGC. Furthermore, we also demonstrated that CdgB is anchored to the cell membrane and localizes potentially to the cell poles. This localization is dependent on the presence of the MHYT domain. In summary, our results suggest that CdgB can provide versatility to signaling modules that control motile and sessile lifestyles in response to key environmental signals in A. baldaniorum.
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Das P, Effmert U, Baermann G, Quella M, Piechulla B. Impact of bacterial volatiles on phytopathogenic fungi: an in vitro study on microbial competition and interaction. JOURNAL OF EXPERIMENTAL BOTANY 2022; 73:596-614. [PMID: 34718549 DOI: 10.1093/jxb/erab476] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/14/2021] [Accepted: 10/27/2021] [Indexed: 06/13/2023]
Abstract
Microorganisms in the rhizosphere are abundant and exist in very high taxonomic diversity. The major players are bacteria and fungi, and bacteria have evolved many strategies to prevail over fungi, among them harmful enzyme activities and noxious secondary metabolites. Interactions between plant growth promoting rhizobacteria and phytopathogenic fungi are potentially valuable since the plant would benefit from fungal growth repression. In this respect, the role of volatile bacterial metabolites in fungistasis has been demonstrated, but the mechanisms of action are less understood. We used three phytopathogenic fungal species (Sclerotinia sclerotiorum, Rhizoctonia solani, and Juxtiphoma eupyrena) as well as one non-phytopathogenic species (Neurospora crassa) and the plant growth promoting rhizobacterium Serratia plymuthica 4Rx13 in co-cultivation assays to investigate the influence of bacterial volatile metabolites on fungi on a cellular level. As a response to the treatment, we found elevated lipid peroxidation, which indirectly reflected the loss of fungal cell membrane integrity. An increase in superoxide dismutase, catalase, and laccase activities indicated oxidative stress. Acclimation to these adverse growth conditions completely restored fungal growth. One of the bioactive bacterial volatile compounds seemed to be ammonia, which was a component of the bacterial volatile mixture. Applied as a single compound in biogenic concentrations ammonia also caused an increase in lipid peroxidation and enzyme activities, but the extent and pattern did not fully match the effect of the entire bacterial volatile mixture.
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Affiliation(s)
- Piyali Das
- Institute of Biological Sciences, Biochemistry, Albert-Einstein-Strasse 3, University of Rostock, 18059 Rostock, Germany
| | - Uta Effmert
- Institute of Biological Sciences, Biochemistry, Albert-Einstein-Strasse 3, University of Rostock, 18059 Rostock, Germany
| | - Gunnar Baermann
- Institute of Biological Sciences, Biochemistry, Albert-Einstein-Strasse 3, University of Rostock, 18059 Rostock, Germany
| | - Manuel Quella
- Institute of Biological Sciences, Biochemistry, Albert-Einstein-Strasse 3, University of Rostock, 18059 Rostock, Germany
| | - Birgit Piechulla
- Institute of Biological Sciences, Biochemistry, Albert-Einstein-Strasse 3, University of Rostock, 18059 Rostock, Germany
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Sierra Cacho D, Zamorano Sánchez DS, Xiqui-Vázquez ML, Viruega Góngora VI, Ramírez-Mata A, Baca BE. CdgC, a Cyclic-di-GMP Diguanylate Cyclase of Azospirillum baldaniorum Is Involved in Internalization to Wheat Roots. FRONTIERS IN PLANT SCIENCE 2021; 12:748393. [PMID: 34745182 PMCID: PMC8564387 DOI: 10.3389/fpls.2021.748393] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 07/27/2021] [Accepted: 09/20/2021] [Indexed: 06/13/2023]
Abstract
Azospirillum baldaniorum is a plant growth-promoting rhizobacterium (PGPR) capable of fixing nitrogen, the synthesis of several phytohormones including indole-acetic acid, and induction of plant defenses against phytopathogens. To establish a successful and prolonged bacteria-plant interaction, A. baldaniorum can form biofilms, bacterial communities embedded in a self-made matrix formed by extracellular polymeric substances which provide favorable conditions for survival. A key modulator of biofilm formation is the second messenger bis-(3'-5')-cyclic-dimeric-GMP (c-di-GMP), which is synthesized by diguanylate cyclases (DGC) and degraded by specific phosphodiesterases. In this study, we analyzed the contribution of a previously uncharacterized diguanylate cyclase designated CdgC, to biofilm formation and bacterial-plant interaction dynamics. We showed that CdgC is capable of altering c-di-GMP levels in a heterologous host, strongly supporting its function as a DGC. The deletion of cdgC resulted in alterations in the three-dimensional structure of biofilms in a nitrogen-source dependent manner. CdgC was required for optimal colonization of wheat roots. Since we also observed that CdgC played an important role in exopolysaccharide production, we propose that this signaling protein activates a physiological response that results in the strong attachment of bacteria to the roots, ultimately contributing to an optimal bacterium-plant interaction. Our results demonstrate that the ubiquitous second messenger c-di-GMP is a key factor in promoting plant colonization by the PGPR A. baldaniorum by allowing proficient internalization in wheat roots. Understanding the molecular basis of PGPR-plant interactions will enable the design of better biotechnological strategies of agro-industrial interest.
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Affiliation(s)
- Daniel Sierra Cacho
- Centro de Investigaciones en Ciencias Microbiológicas, Benemérita Universidad Autónoma de Puebla, Ciudad Universitaria, Puebla, Mexico
| | - David S. Zamorano Sánchez
- Programa de Biología de Sistemas y Biología Sintética, Centro de Ciencias Genómicas, Universidad Nacional Autónoma de México, Cuernavaca, Mexico
| | - Maria Luisa Xiqui-Vázquez
- Centro de Investigaciones en Ciencias Microbiológicas, Benemérita Universidad Autónoma de Puebla, Ciudad Universitaria, Puebla, Mexico
| | - Víctor Iván Viruega Góngora
- Centro de Investigaciones en Ciencias Microbiológicas, Benemérita Universidad Autónoma de Puebla, Ciudad Universitaria, Puebla, Mexico
| | - Alberto Ramírez-Mata
- Centro de Investigaciones en Ciencias Microbiológicas, Benemérita Universidad Autónoma de Puebla, Ciudad Universitaria, Puebla, Mexico
| | - Beatriz E. Baca
- Centro de Investigaciones en Ciencias Microbiológicas, Benemérita Universidad Autónoma de Puebla, Ciudad Universitaria, Puebla, Mexico
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Specific Root Exudate Compounds Sensed by Dedicated Chemoreceptors Shape Azospirillum brasilense Chemotaxis in the Rhizosphere. Appl Environ Microbiol 2020; 86:AEM.01026-20. [PMID: 32471917 DOI: 10.1128/aem.01026-20] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2020] [Accepted: 05/20/2020] [Indexed: 12/15/2022] Open
Abstract
Plant roots shape the rhizosphere community by secreting compounds that recruit diverse bacteria. Colonization of various plant roots by the motile alphaproteobacterium Azospirillum brasilens e causes increased plant growth, root volume, and crop yield. Bacterial chemotaxis in this and other motile soil bacteria is critical for competitive colonization of the root surfaces. The role of chemotaxis in root surface colonization has previously been established by endpoint analyses of bacterial colonization levels detected a few hours to days after inoculation. More recently, microfluidic devices have been used to study plant-microbe interactions, but these devices are size limited. Here, we use a novel slide-in chamber that allows real-time monitoring of plant-microbe interactions using agriculturally relevant seedlings to characterize how bacterial chemotaxis mediates plant root surface colonization during the association of A. brasilens e with Triticum aestivum (wheat) and Medicago sativa (alfalfa) seedlings. We track A. brasilense accumulation in the rhizosphere and on the root surfaces of wheat and alfalfa. A. brasilense motile cells display distinct chemotaxis behaviors in different regions of the roots, including attractant and repellent responses that ultimately drive surface colonization patterns. We also combine these observations with real-time analyses of behaviors of wild-type and mutant strains to link chemotaxis responses to distinct chemicals identified in root exudates to specific chemoreceptors that together explain the chemotactic response of motile cells in different regions of the roots. Furthermore, the bacterial second messenger c-di-GMP modulates these chemotaxis responses. Together, these findings illustrate dynamic bacterial chemotaxis responses to rhizosphere gradients that guide root surface colonization.IMPORTANCE Plant root exudates play critical roles in shaping rhizosphere microbial communities, and the ability of motile bacteria to respond to these gradients mediates competitive colonization of root surfaces. Root exudates are complex chemical mixtures that are spatially and temporally dynamic. Identifying the exact chemical(s) that mediates the recruitment of soil bacteria to specific regions of the roots is thus challenging. Here, we connect patterns of bacterial chemotaxis responses and sensing by chemoreceptors to chemicals found in root exudate gradients and identify key chemical signals that shape root surface colonization in different plants and regions of the roots.
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8
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Grenga L, Little RH, Chandra G, Woodcock SD, Saalbach G, Morris RJ, Malone JG. Control of mRNA translation by dynamic ribosome modification. PLoS Genet 2020; 16:e1008837. [PMID: 32584816 PMCID: PMC7343187 DOI: 10.1371/journal.pgen.1008837] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2020] [Revised: 07/08/2020] [Accepted: 05/07/2020] [Indexed: 01/28/2023] Open
Abstract
Control of mRNA translation is a crucial regulatory mechanism used by bacteria to respond to their environment. In the soil bacterium Pseudomonas fluorescens, RimK modifies the C-terminus of ribosomal protein RpsF to influence important aspects of rhizosphere colonisation through proteome remodelling. In this study, we show that RimK activity is itself under complex, multifactorial control by the co-transcribed phosphodiesterase trigger enzyme (RimA) and a polyglutamate-specific protease (RimB). Furthermore, biochemical experimentation and mathematical modelling reveal a role for the nucleotide second messenger cyclic-di-GMP in coordinating these activities. Active ribosome regulation by RimK occurs by two main routes: indirectly, through changes in the abundance of the global translational regulator Hfq and directly, with translation of surface attachment factors, amino acid transporters and key secreted molecules linked specifically to RpsF modification. Our findings show that post-translational ribosomal modification functions as a rapid-response mechanism that tunes global gene translation in response to environmental signals.
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Affiliation(s)
- Lucia Grenga
- Molecular Microbiology, John Innes Centre, Norwich, Norfolk, United Kingdom
- School of Biological Sciences, University of East Anglia, Norwich, Norfolk, United Kingdom
| | | | - Govind Chandra
- Molecular Microbiology, John Innes Centre, Norwich, Norfolk, United Kingdom
| | | | - Gerhard Saalbach
- Molecular Microbiology, John Innes Centre, Norwich, Norfolk, United Kingdom
| | - Richard James Morris
- Computational and Systems Biology, John Innes Centre, Norwich, Norfolk, United Kingdom
| | - Jacob George Malone
- Molecular Microbiology, John Innes Centre, Norwich, Norfolk, United Kingdom
- School of Biological Sciences, University of East Anglia, Norwich, Norfolk, United Kingdom
- * E-mail:
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Thompson CM, Malone JG. Nucleotide second messengers in bacterial decision making. Curr Opin Microbiol 2020; 55:34-39. [PMID: 32172083 PMCID: PMC7322531 DOI: 10.1016/j.mib.2020.02.006] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2019] [Revised: 02/04/2020] [Accepted: 02/10/2020] [Indexed: 12/28/2022]
Abstract
Structural analysis of NSM regulators reveals new mechanisms of NSM signalling. NSM proteins binding multiple ligands support crosstalk between signalling networks. NSM networks control structure and heterogeneity in complex microbial communities. The diversity of bacterial NSM regulators is far higher than previously thought. The (p)ppApp toxin suggests non-signalling roles exist for bacterial NSMs.
Since the initial discovery of bacterial nucleotide second messengers (NSMs), we have made huge progress towards understanding these complex signalling networks. Many NSM networks contain dozens of metabolic enzymes and binding targets, whose activity is tightly controlled at every regulatory level. They function as global regulators and in specific signalling circuits, controlling multiple aspects of bacterial behaviour and development. Despite these advances there is much still to discover, with current research focussing on the molecular mechanisms of signalling circuits, the role of the environment in controlling NSM pathways and attempts to understand signalling at the whole cell/community level. Here we examine recent developments in the NSM signalling field and discuss their implications for understanding this important driver of microbial behaviour.
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Affiliation(s)
- Catriona Ma Thompson
- Molecular Microbiology Department, John Innes Centre, Norwich, UK; School of Biological Sciences, University of East Anglia, Norwich, UK
| | - Jacob G Malone
- Molecular Microbiology Department, John Innes Centre, Norwich, UK; School of Biological Sciences, University of East Anglia, Norwich, UK.
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Structural Conservation and Diversity of PilZ-Related Domains. J Bacteriol 2020; 202:JB.00664-19. [PMID: 31740493 DOI: 10.1128/jb.00664-19] [Citation(s) in RCA: 18] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2019] [Accepted: 11/12/2019] [Indexed: 01/13/2023] Open
Abstract
The widespread bacterial second messenger cyclic diguanylate (c-di-GMP) regulates a variety of processes, including protein secretion, motility, cell development, and biofilm formation. c-di-GMP-dependent responses are often mediated by its binding to the cytoplasmic receptors that contain the PilZ domain. Here, we present comparative structural and sequence analysis of various PilZ-related domains and describe three principal types of them: (i) the canonical PilZ domain, whose structure includes a six-stranded beta-barrel and a C-terminal alpha helix, (ii) an atypical PilZ domain that contains two extra alpha helices and forms stable tetramers, and (iii) divergent PilZ-related domains, which include the eponymous PilZ protein and PilZN (YcgR_N) and PilZNR (YcgR_2) domains. We refine the second c-di-GMP binding motif of PilZ as [D/N]hSXXG and show that the hydrophobic residue h of this motif interacts with a cluster of conserved hydrophobic residues, helping maintain the PilZ domain fold. We describe several novel PilZN-type domains that are fused to the canonical PilZ domains in specific taxa, such as spirochetes, actinobacteria, aquificae, cellulose-degrading clostridia, and deltaproteobacteria. We propose that the evolution of the three major groups of PilZ domains included (i) fusion of pilZ with other genes, which produced Alg44, cellulose synthase, and other multidomain proteins; (ii) insertion of an ∼200-bp fragment, which resulted in the formation of tetramer-forming PilZ proteins; and (iii) tandem duplication of pilZ genes, which led to the formation of PilZ dimers and YcgR-like proteins.IMPORTANCE c-di-GMP is a ubiquitous bacterial second messenger that regulates motility, biofilm formation, and virulence of many bacterial pathogens. The PilZ domain is a widespread c-di-GMP receptor that binds c-di-GMP through its RXXXR and [D/N]hSXXG motifs; some PilZ domains lack these motifs and are unable to bind c-di-GMP. We used structural and sequence analysis to assess the diversity of PilZ-related domains and define their common features. We show that the hydrophobic residue h in the second position of the second motif is highly conserved; it may serve as a readout for c-di-GMP binding. We describe three principal classes of PilZ-related domains, canonical, tetramer-forming, and divergent PilZ domains, and propose the evolutionary pathways that led to the emergence of these PilZ types.
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