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Frontiers in Cellular and Infection... 2014Biological nitrogen fixation (BNF) is a process in which the atmospheric nitrogen (N2) is transformed into ammonia (NH3) by a select group of nitrogen-fixing organisms,... (Review)
Review
Biological nitrogen fixation (BNF) is a process in which the atmospheric nitrogen (N2) is transformed into ammonia (NH3) by a select group of nitrogen-fixing organisms, or diazotrophic bacteria. In order to furnish the biologically useful nitrogen to plants, these bacteria must be in constant molecular communication with their host plants. Some of these molecular plant-microbe interactions are very specific, resulting in a symbiotic relationship between the diazotroph and the host. Others are found between associative diazotrophs and plants, resulting in plant infection and colonization of internal tissues. Independent of the type of ecological interaction, glycans, and glycoconjugates produced by these bacteria play an important role in the molecular communication prior and during colonization. Even though exopolysaccharides (EPS) and lipochitooligosaccharides (LCO) produced by diazotrophic bacteria and released onto the environment have their importance in the microbe-plant interaction, it is the lipopolysaccharides (LPS), anchored on the external membrane of these bacteria, that mediates the direct contact of the diazotroph with the host cells. These molecules are extremely variable among the several species of nitrogen fixing-bacteria, and there are evidences of the mechanisms of infection being closely related to their structure.
Topics: Bacterial Physiological Phenomena; Endophytes; Lipopolysaccharides; Nitrogen; Nitrogen Fixation; Rhizobiaceae
PubMed: 25232535
DOI: 10.3389/fcimb.2014.00119 -
Molecules (Basel, Switzerland) Nov 2021Legumes form a symbiosis with rhizobia, a soil bacterium that allows them to access atmospheric nitrogen and deliver it to the plant for growth. Biological nitrogen... (Review)
Review
Legumes form a symbiosis with rhizobia, a soil bacterium that allows them to access atmospheric nitrogen and deliver it to the plant for growth. Biological nitrogen fixation occurs in specialized organs, termed nodules, that develop on the legume root system and house nitrogen-fixing rhizobial bacteroids in organelle-like structures termed symbiosomes. The process is highly energetic and there is a large demand for carbon by the bacteroids. This carbon is supplied to the nodule as sucrose, which is broken down in nodule cells to organic acids, principally malate, that can then be assimilated by bacteroids. Sucrose may move through apoplastic and/or symplastic routes to the uninfected cells of the nodule or be directly metabolised at the site of import within the vascular parenchyma cells. Malate must be transported to the infected cells and then across the symbiosome membrane, where it is taken up by bacteroids through a well-characterized system. The dicarboxylate transporters on the infected cell and symbiosome membranes have been functionally characterized but remain unidentified. Proteomic and transcriptomic studies have revealed numerous candidates, but more work is required to characterize their function and localise the proteins in planta. GABA, which is present at high concentrations in nodules, may play a regulatory role, but this remains to be explored.
Topics: Biological Transport; Fabaceae; Malates; Nitrogen Fixation; Rhizobiaceae; Root Nodules, Plant; Symbiosis
PubMed: 34833968
DOI: 10.3390/molecules26226876 -
Current Opinion in Biotechnology Aug 2021Huanglongbing (HLB) disease is threatening the sustainability of citriculture in affected regions because of its rapid spread and the severity of the symptoms it... (Review)
Review
Huanglongbing (HLB) disease is threatening the sustainability of citriculture in affected regions because of its rapid spread and the severity of the symptoms it induces. Herein, we summarise the main research findings that can be exploited to develop HLB-resistant cultivars. A major bottleneck has been the lack of a system for the ex vivo cultivation of HLB-associated bacteria (CLs) in true plant hosts, which precludes the evaluation of target genes/metabolites in reliable plant/pathogen/vector environments. With regard to HLB vectors, several biotechnologies which have been proven in laboratory settings to be effective for insect control are presented. Finally, new genotypes that are resistant to CLs or their insect vectors are described, and the most relevant strategies for fighting HLB are highlighted.
Topics: Animals; Citrus; Hemiptera; Insect Vectors; Plant Diseases; Rhizobiaceae
PubMed: 34198205
DOI: 10.1016/j.copbio.2021.06.003 -
Canadian Journal of Microbiology Oct 2016Huanglongbing (HLB) is the most destructive disease of citrus worldwide. Monitoring of health and detection of diseases in trees is critical for sustainable agriculture.... (Review)
Review
Huanglongbing (HLB) is the most destructive disease of citrus worldwide. Monitoring of health and detection of diseases in trees is critical for sustainable agriculture. HLB symptoms are virtually the same wherever the disease occurs. The disease is caused by Candidatus Liberibacter spp., vectored by the psyllids Diaphorina citri Kuwayama and Trioza erytreae. Electron microscopy was the first technique used for HLB detection. Nowadays, scientists are working on the development of new techniques for a rapid HLB detection, as there is no sensor commercially accessible for real-time assessment of health conditions in trees. Currently, the most widely used mechanism for monitoring HLB is exploration, which is an expensive, labor-intensive, and time-consuming process. Molecular techniques such as polymerase chain reaction are used for the identification of HLB disease, which requires detailed sampling and processing procedures. Furthermore, investigations are ongoing in spectroscopic and imaging techniques, profiling of plant volatile organic compounds, and isothermal amplification. This study recognizes the need for developing a rapid, cost-effective, and reliable health-monitoring sensor that would facilitate advancements in HLB disease detection. This paper compares the benefits and limitations of these potential methods for HLB detection.
Topics: Animals; Biomarkers; Citrus; Molecular Typing; Plant Diseases; Polymerase Chain Reaction; Rhizobiaceae
PubMed: 27590666
DOI: 10.1139/cjm-2016-0022 -
Plant, Cell & Environment Jun 2009Root-secreted chemicals mediate multi-partite interactions in the rhizosphere, where plant roots continually respond to and alter their immediate environment. Increasing... (Review)
Review
Root-secreted chemicals mediate multi-partite interactions in the rhizosphere, where plant roots continually respond to and alter their immediate environment. Increasing evidence suggests that root exudates initiate and modulate dialogue between roots and soil microbes. For example, root exudates serve as signals that initiate symbiosis with rhizobia and mycorrhizal fungi. In addition, root exudates maintain and support a highly specific diversity of microbes in the rhizosphere of a given particular plant species, thus suggesting a close evolutionary link. In this review, we focus mainly on compiling the information available on the regulation and mechanisms of root exudation processes, and provide some ideas related to the evolutionary role of root exudates in shaping soil microbial communities.
Topics: Biological Evolution; Mycorrhizae; Plant Physiological Phenomena; Plant Roots; Rhizobiaceae; Soil; Soil Microbiology; Species Specificity; Symbiosis
PubMed: 19143988
DOI: 10.1111/j.1365-3040.2008.01926.x -
Microbiological Reviews Jun 1994Cyclic beta-glucans are low-molecular-weight cell surface carbohydrates that are found almost exclusively in bacteria of the Rhizobiaceae family. These glucans are major... (Review)
Review
Cyclic beta-glucans are low-molecular-weight cell surface carbohydrates that are found almost exclusively in bacteria of the Rhizobiaceae family. These glucans are major cellular constituents, and under certain culture conditions their levels may reach up to 20% of the total cellular dry weight. In Agrobacterium and Rhizobium species, these molecules contain between 17 and 40 glucose residues linked solely by beta-(1,2) glycosidic bonds. In Bradyrhizobium species, the cyclic beta-glucans are smaller (10 to 13 glucose residues) and contain glucose linked by both beta-(1,6) and beta-(1,3) glycosidic bonds. In some rhizobial strains, the cyclic beta-glucans are unsubstituted, whereas in other rhizobia these molecules may become highly substituted with moieties such as sn-1-phosphoglycerol. To date, two genetic loci specifically associated with cyclic beta-glucan biosynthesis have been identified in Rhizobium (ndvA and ndvB) and Agrobacterium (chvA and chvB) species. Mutants with mutations at these loci have been shown to be impaired in their ability to grow in hypoosmotic media, have numerous alterations in their cell surface properties, and are also impaired in their ability to infect plants. The present review will examine the structure and occurrence of the cyclic beta-glucans in a variety of species of the Rhizobiaceae. The possible functions of these unique molecules in the free-living bacteria as well as during plant infection will be discussed.
Topics: ATP-Binding Cassette Transporters; Adaptation, Physiological; Bacterial Proteins; Biological Transport; Carbohydrate Conformation; Chromosomes, Bacterial; DNA-Binding Proteins; Glucans; Hypotonic Solutions; Industrial Microbiology; Membrane Proteins; Plants; Rhizobiaceae; Symbiosis; Virulence; Virulence Factors; beta-Glucans
PubMed: 8078434
DOI: 10.1128/mr.58.2.145-161.1994 -
International Journal of Systematic and... Mar 2022The alphaproteobacterial family is highly diverse, with 168 species with validly published names classified into 17 genera with validly published names. Most named...
The alphaproteobacterial family is highly diverse, with 168 species with validly published names classified into 17 genera with validly published names. Most named genera in this family are delineated based on genomic relatedness and phylogenetic relationships, but some historically named genera show inconsistent distribution and phylogenetic breadth. The most problematic is , which is notorious for being highly paraphyletic, as most newly described species in the family are assigned to this genus without consideration of their proximity to existing genera, or the need to create novel genera. Moreover, many genera lack synapomorphic traits that would give them biological and ecological significance. We propose a common framework for genus delimitation within the family , wherein genera are defined as monophyletic groups in a core-genome gene phylogeny, that are separated from related species using a pairwise core-proteome average amino acid identity (cpAAI) threshold of approximately 86 %. We further propose that additional genomic or phenotypic evidence can justify division of species into separate genera even if they share greater than 86 % cpAAI. Applying this framework, we propose to reclassify and into gen. nov. Data is also provided to support the formation of comb. nov., comb. nov., comb. nov., comb. nov., comb. nov. and comb. nov. Lastly, we present arguments that the unification of the genera and in Opinion 84 of the Judicial Commission is no longer justified by current genomic and phenotypic data. Despite pairwise cpAAI values for all species and all species being >86 %, additional genomic and phenotypic data suggest that they significantly differ in their biology and ecology. We therefore propose emended descriptions of and , which we argue should be considered as separate genera.
Topics: Bacterial Typing Techniques; Base Composition; DNA, Bacterial; Fatty Acids; Phylogeny; RNA, Ribosomal, 16S; Rhizobiaceae; Rhizobium; Sequence Analysis, DNA
PubMed: 35238735
DOI: 10.1099/ijsem.0.005243 -
Phytopathology Apr 2017The Huanglongbing (HLB) disease pyramid is composed of Liberibacters, psyllid vectors, citrus hosts, and the environment. The epidemiological outcomes for... (Review)
Review
The Huanglongbing (HLB) disease pyramid is composed of Liberibacters, psyllid vectors, citrus hosts, and the environment. The epidemiological outcomes for Liberibacter-associated plant diseases are collectively determined by the inherent relationships among plant-Liberibacters-psyllids, and how various environmental factors affect plant-Liberibacter-psyllid interactions. Citrus-Liberibacter-psyllid interactions occur in a complex microbiome system. In this review, we focus on the progress in understanding the HLB disease pyramid, and how the microbiome affects the HLB disease pyramid including the interaction between HLB and the citrus microbiome; the interaction between Liberibacters and psyllids; the interaction between Liberibacters and gut microbiota in psyllids; and the effect of HLB on selected above- and belowground citrus pathogens. Their implications for HLB management are also discussed.
Topics: Animals; Citrus; Hemiptera; Host-Pathogen Interactions; Microbiota; Plant Diseases; Rhizobiaceae
PubMed: 28095208
DOI: 10.1094/PHYTO-12-16-0426-RVW -
Journal of Bacteriology May 2021Rhizobia are a phylogenetically diverse group of soil bacteria that engage in mutualistic interactions with legume plants. Although specifics of the symbioses differ...
Rhizobia are a phylogenetically diverse group of soil bacteria that engage in mutualistic interactions with legume plants. Although specifics of the symbioses differ between strains and plants, all symbioses ultimately result in the formation of specialized root nodule organs that host the nitrogen-fixing microsymbionts called bacteroids. Inside nodules, bacteroids encounter unique conditions that necessitate the global reprogramming of physiological processes and the rerouting of their metabolism. Decades of research have addressed these questions using genetics, omics approaches, and, more recently, computational modeling. Here, we discuss the common adaptations of rhizobia to the nodule environment that define the core principles of bacteroid functioning. All bacteroids are growth arrested and perform energy-intensive nitrogen fixation fueled by plant-provided C-dicarboxylates at nanomolar oxygen levels. At the same time, bacteroids are subject to host control and sanctioning that ultimately determine their fitness and have fundamental importance for the evolution of a stable mutualistic relationship.
Topics: Adaptation, Physiological; Biological Evolution; Nitrogen Fixation; Plant Root Nodulation; Plant Roots; Rhizobiaceae
PubMed: 33526611
DOI: 10.1128/JB.00539-20 -
Current Biology : CB Sep 2011Research on life history strategies of microbial symbionts is key to understanding the evolution of cooperation with hosts, but also their survival between hosts.... (Review)
Review
Research on life history strategies of microbial symbionts is key to understanding the evolution of cooperation with hosts, but also their survival between hosts. Rhizobia are soil bacteria known for fixing nitrogen inside legume root nodules. Arbuscular mycorrhizal (AM) fungi are ubiquitous root symbionts that provide plants with nutrients and other benefits. Both kinds of symbionts employ strategies to reproduce during symbiosis using host resources; to repopulate the soil; to survive in the soil between hosts; and to find and infect new hosts. Here we focus on the fitness of the microbial symbionts and how interactions at each of these stages has shaped microbial life-history strategies. During symbiosis, microbial fitness could be increased by diverting more resources to individual reproduction, but that may trigger fitness-reducing host sanctions. To survive in the soil, symbionts employ sophisticated strategies, such as persister formation for rhizobia and reversal of spore germination by mycorrhizae. Interactions among symbionts, from rhizobial quorum sensing to fusion of genetically distinct fungal hyphae, increase adaptive plasticity. The evolutionary implications of these interactions and of microbial strategies to repopulate and survive in the soil are largely unexplored.
Topics: Biological Evolution; Hyphae; Mycorrhizae; Plants; Rhizobiaceae; Soil Microbiology; Spores, Fungal; Symbiosis
PubMed: 21959168
DOI: 10.1016/j.cub.2011.06.018