Rhizobial Chemotaxis and Motility Systems at Work in the Soil

Bacteria navigate their way often as individual cells through their chemical and biological environment in aqueous medium or across solid surfaces. They swim when starved or in response to physical and chemical stimuli. Flagella-driven chemotaxis in bacteria has emerged as a paradigm for both signal transduction and cellular decision-making. By altering motility, bacteria swim toward nutrient-rich environments, movement modulated by their chemotaxis systems with the addition of pili for surface movement. The numbers and types of chemoreceptors reflect the bacterial niche and lifestyle, with those adapted to complex environments having diverse metabolic capabilities, encoding far more chemoreceptors in their genomes. The Alpha-proteobacteria typify the latter case, with soil bacteria such as rhizobia, endosymbionts of legume plants, where motility and chemotaxis are essential for competitive symbiosis initiation, among other processes. This review describes the current knowledge of motility and chemotaxis in six model soil bacteria: Sinorhizobium meliloti, Agrobacterium fabacearum, Rhizobium leguminosarum, Azorhizobium caulinodans, Azospirillum brasilense, and Bradyrhizobium diazoefficiens. Although motility and chemotaxis systems have a conserved core, rhizobia possess several modifications that optimize their movements in soil and root surface environments. The soil provides a unique challenge for microbial mobility, since water pathways through particles are not always continuous, especially in drier conditions. The effectiveness of symbiont inoculants in a field context relies on their mobility and dispersal through the soil, often assisted by water percolation or macroorganism movement or networks. Thus, this review summarizes the factors that make it essential to consider and test rhizobial motility and chemotaxis for any potential inoculant.

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Diversity and numbers of root-nodule bacteria (rhizobia) in Polish soils

Acta Societatis Botanicorum Poloniae ◽

10.5586/asbp.2005.012 ◽

2011 ◽

Vol 74 (1) ◽

pp. 83-86 ◽

Cited By ~ 8

Author(s):

Stefan Martyniuk ◽

Jadwiga Oroń ◽

Maria Martyniuk

Keyword(s):

Sinorhizobium Meliloti ◽

Rhizobium Leguminosarum ◽

Root Nodule ◽

Chemical Properties ◽

Physical And Chemical Properties ◽

Nodule Bacteria ◽

Root Nodule Bacteria ◽

Plant Infection ◽

Physical And Chemical ◽

And Chemical Properties

Using a sand pouch-plant infection method, populations of several species of root-nodule bacteria (rhizobia) were enumerated in eighty soils collected throughout Poland. Rhizobium leguminosarum bv. viciae (symbionts of pea, faba bean, vetch) and R. leguminosarum bv. trifolii (symbionts of clover) were detected in 77 and 76 soils, respectively. Most of these soils contained moderate and high numbers of these species of the rhizobia. Symbionts of beans, R. leguminosarum bv. phaseoli, were assessed in 76 soils; of this number 15 soils had no detectable populations of bean rhizobia and in 40 soils high or moderate numbers of these bacteria were found. Bradyrhizobium sp. (Lupinus), root-nodule bacteria of lupine and serradella, were absent in 19 soils, out of 80 tested, and 34 soils were colonised by high or moderate populations of bradyrhizobia. Sinorhizobium meliloti, rhizobia nodulating alfalfa, were sparse in the examined soils; with 56 soil containing no detectable numbers of S. meliloti and only 6 soils harbouring high or moderate populations of this species. The estimated numbers of the rhizobia in the studied soils were also related to some physical and chemical properties of these soils.

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Potential Use of Azotobacter chroococcum in Crop Production: An Overview

Current Agriculture Research Journal ◽

10.12944/carj.1.1.04 ◽

2013 ◽

Vol 1 (1) ◽

pp. 35-38 ◽

Cited By ~ 39

Author(s):

Sartaj Wani ◽

Subhash Chand ◽

Tahir Ali

Keyword(s):

Plant Nutrition ◽

Soil Bacteria ◽

Crop Production ◽

Higher Plants ◽

Root Surface ◽

Azotobacter Chroococcum ◽

Growth Substances ◽

Plant Genotype ◽

High Effectiveness ◽

Potential Use

Research on Azotobacter chroococcum spp. in crop production has manifested its significance in plant nutrition and its contribution to soil fertility. The possibility of using Azotobacter chroococcum in research experiments as microbial inoculant through production of growth substances and their effects on the plant has markedly enhanced crop production in agriculture. Being soil bacteria, Azotobacteria genus synthesizes auxins, cytokinins, and GA–like substances, and these growth materials are the primary substances controlling the enhanced growth. These hormonal substances, which originate from the rhizosphere or root surface, affect the growth of the closely associated higher plants. In order to guarantee the high effectiveness of inoculants and microbiological fertilizers it is necessary to find the compatible partners, i.e. a particular plant genotype and a particular Azotobacter strain that will form a good association.

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A rhizobial homolog of IHF stimulates transcription of dctA in Rhizobium leguminosarum but not in Sinorhizobium meliloti

Gene ◽

10.1016/s0378-1119(99)00366-2 ◽

1999 ◽

Vol 238 (2) ◽

pp. 489-500 ◽

Cited By ~ 3

Author(s):

John Sojda ◽

Baohua Gu ◽

Joon Lee ◽

Timothy R Hoover ◽

B.Tracy Nixon

Keyword(s):

Sinorhizobium Meliloti ◽

Rhizobium Leguminosarum

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Sinorhizobium meliloti YbeY is a zinc-dependent single-strand specific endoribonuclease that plays an important role in 16S ribosomal RNA processing

Nucleic Acids Research ◽

10.1093/nar/gkz1095 ◽

2019 ◽

Vol 48 (1) ◽

pp. 332-348 ◽

Cited By ~ 3

Author(s):

Vignesh M P Babu ◽

Siva Sankari ◽

James A Budnick ◽

Clayton C Caswell ◽

Graham C Walker

Keyword(s):

16S Rrna ◽

Metal Ion ◽

Sinorhizobium Meliloti ◽

Single Strand ◽

Rrna Processing ◽

E Coli ◽

Gamma Proteobacteria ◽

Ribosomal Rna Processing ◽

Alpha Proteobacteria ◽

Endoribonuclease Activity

Abstract Single-strand specific endoribonuclease YbeY has been shown to play an important role in the processing of the 3′ end of the 16S rRNA in Escherichia coli. Lack of YbeY results in the accumulation of the 17S rRNA precursor. In contrast to a previous report, we show that Sinorhizobium meliloti YbeY exhibits endoribonuclease activity on single-stranded RNA substrate but not on the double-stranded substrate. This study also identifies the previously unknown metal ion involved in YbeY function to be Zn2+ and shows that the activity of YbeY is enhanced when the occupancy of zinc is increased. We have identified a pre-16S rRNA precursor that accumulates in the S. meliloti ΔybeY strain. We also show that ΔybeY mutant of Brucella abortus, a mammalian pathogen, also accumulates a similar pre-16S rRNA. The pre-16S species is longer in alpha-proteobacteria than in gamma-proteobacteria. We demonstrate that the YbeY from E. coli and S. meliloti can reciprocally complement the rRNA processing defect in a ΔybeY mutant of the other organism. These results establish YbeY as a zinc-dependent single-strand specific endoribonuclease that functions in 16S rRNA processing in both alpha- and gamma-proteobacteria.

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Periodic Variability on Time-scales of Decades to Centuries in Magnetic Ap Stars: Challenges and Strategies

Proceedings of the International Astronomical Union ◽

10.1017/s1743921318002338 ◽

2017 ◽

Vol 14 (S339) ◽

pp. 106-109

Author(s):

G. Mathys

Keyword(s):

Time Scales ◽

Current Knowledge ◽

Main Sequence Stars ◽

Unique Challenge ◽

Origin And Evolution ◽

Rotation Periods ◽

Orbital Periods ◽

The One ◽

Ap Stars ◽

Incomplete Picture

AbstractRecent studies have revealed the existence of a significant population of Ap stars with extremely long rotation periods, and the frequent occurrence of Ap stars in wide binaries. Those results represent new constraints on the understanding of the origin and evolution of Ap stars, and (by extension) of all upper-main-sequence stars. Current knowledge of Ap stars with the longest rotation and orbital periods remains incomplete, on the one hand because in many cases the periods of interest are longer than the time-spans over which relevant observations have been obtained, and on the other hand because some important subsets of Ap stars have been omitted from the studies that have been carried out until now. Additional observations over time-scales of decades to centuries are needed to complement the current incomplete picture. Securing them with the required accuracy and time coverage, and ensuring that their full exploitation will ultimately be possible, represents a unique challenge in time-domain astronomy.

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The Chemical Composition of the Wolf-Rayet Stars

Symposium - International Astronomical Union ◽

10.1017/s0074180900028734 ◽

1982 ◽

Vol 99 ◽

pp. 87-104 ◽

Cited By ~ 4

Author(s):

Allan J. Willis

Keyword(s):

Chemical Composition ◽

Evolutionary Theory ◽

Current Knowledge ◽

Chemical Properties ◽

Analytical Models ◽

Evolutionary Status ◽

Chemical Abundances ◽

Considerable Uncertainty ◽

C And N ◽

Physical And Chemical

This review summarises current knowledge of the chemical composition of PopI WR stars, concentrating on work carried out in this area since the last IAU, No. 49, symposium devoted to this stellar class (Bappu & Sahade 1973). Earlier reviews of this topic are found in Gebbie & Thomas (1968). The dichotomy of the WR stars into the WN and WC sequences (Beals 1934) has generally been qualitatively interpreted as arising because of gross differences in the C and N abundances: WN stars which exhibit emission lines of predominantly He and N ions with little evidence for C, being inferred as C-poor objects, whilst WC stars, showing predominantly He and C lines and virtually no evidence for N being inferred as N-poor. In both sequences the visible spectra show little or no evidence for hydrogen. However, although the WR stars have been acknowledged as a class for over a century now, progress has been very slow in putting quantitative determinations of their physical and chemical properties on a firm basis, with the bulk of work in this area being conducted during the past decade. The chemical nature of the WR stars has always been a matter of considerable uncertainty, controversy and, quite often, passionate disagreement, arising from uncertainties in the interpretation of the, often ambiguous, observational material available, as well as from disagreements as to the reliability of the use of comparatively simple analytical models employed to date. Recent results strongly suggest that the WR stars are chemically evolved objects, with low H/He ratios and quite different C/N ratios in the WN and WC sequences, with some measure of agreement in these results with the chemistries predicted to arise at various stages of evolutionary theory for hot massive stars which, by one means or another, have shed much of their atmospheric material during their evolution. My purpose in this review is to summarise the investigations and results that lead to the above conclusions. §2 deals with an assessment of the atmospheric H/He ratio in both WN and WC stars: a parameter of fundamental importance in addressing their evolutionary status, as well as providing a base species with which to compare other derived chemical abundances. §3 briefly deals with the models generally employed and gives recent results for He, C and N abundances derived from both visible and UV line analyses. §4 summarises recent results from stellar evolutionary theory and in §5 compares these with those derived from observation, assessing the significance of these new results and their implications for the evolutionary status of the WR stars. Some areas for further advancement are identified.

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Binding Site Determinants for the LysR-Type Transcriptional Regulator PcaQ in the Legume Endosymbiont Sinorhizobium meliloti

Journal of Bacteriology ◽

10.1128/jb.01456-07 ◽

2007 ◽

Vol 190 (4) ◽

pp. 1237-1246 ◽

Cited By ~ 15

Author(s):

Allyson M. MacLean ◽

Michelle I. Anstey ◽

Turlough M. Finan

Keyword(s):

Binding Site ◽

Sinorhizobium Meliloti ◽

Rhizobium Leguminosarum ◽

Transcriptional Start Site ◽

Mesorhizobium Loti ◽

Equilibrium Dissociation ◽

Dyad Symmetry

ABSTRACT LysR-type transcriptional regulators represent one of the largest groups of prokaryotic regulators described to date. In the gram-negative legume endosymbiont Sinorhizobium meliloti, enzymes involved in the protocatechuate branch of the β-ketoadipate pathway are encoded within the pcaDCHGB operon, which is subject to regulation by the LysR-type protein PcaQ. In this work, purified PcaQ was shown to bind strongly (equilibrium dissociation constant, 0.54 nM) to a region at positions −78 to −45 upstream of the pcaD transcriptional start site. Within this region, we defined a PcaQ binding site with dyad symmetry that is required for regulation of pcaD expression in vivo and for binding of PcaQ in vitro. We also demonstrated that PcaQ participates in negative autoregulation by monitoring expression of pcaQ via a transcriptional fusion to lacZ. Although pcaQ homologues are present in many α-proteobacteria, this work describes the first reported purification of this regulator, as well as characterization of its binding site, which is conserved in Agrobacterium tumefaciens, Rhizobium leguminosarum, Rhizobium etli, and Mesorhizobium loti.

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Succinate Transport Is Not Essential for Symbiotic Nitrogen Fixation by Sinorhizobium meliloti or Rhizobium leguminosarum

Applied and Environmental Microbiology ◽

10.1128/aem.01561-17 ◽

2017 ◽

Vol 84 (1) ◽

Cited By ~ 10

Author(s):

Michael J. Mitsch ◽

George C. diCenzo ◽

Alison Cowie ◽

Turlough M. Finan

Keyword(s):

Nitrogen Fixation ◽

Carbon Source ◽

Sinorhizobium Meliloti ◽

Rhizobium Leguminosarum ◽

Symbiotic Nitrogen Fixation ◽

Sequencing Analysis ◽

Wild Type ◽

Content Type ◽

Transcriptional Changes ◽

Symbiotic Properties

ABSTRACTSymbiotic nitrogen fixation (SNF) is an energetically expensive process performed by bacteria during endosymbiotic relationships with plants. The bacteria require the plant to provide a carbon source for the generation of reductant to power SNF. While C4-dicarboxylates (succinate, fumarate, and malate) appear to be the primary, if not sole, carbon source provided to the bacteria, the contribution of each C4-dicarboxylate is not known. We address this issue using genetic and systems-level analyses. Expression of a malate-specific transporter (MaeP) inSinorhizobium melilotiRm1021dctmutants unable to transport C4-dicarboxylates resulted in malate import rates of up to 30% that of the wild type. This was sufficient to support SNF withMedicago sativa, with acetylene reduction rates of up to 50% those of plants inoculated with wild-typeS. meliloti.Rhizobium leguminosarumbv. viciae 3841dctmutants unable to transport C4-dicarboxylates but expressing themaePtransporter had strong symbiotic properties, withPisum sativumplants inoculated with these strains appearing similar to plants inoculated with wild-typeR. leguminosarum. This was despite malate transport rates by the mutant bacteroids being 10% those of the wild type. An RNA-sequencing analysis of the combinedP. sativum-R. leguminosarumnodule transcriptome was performed to identify systems-level adaptations in response to the inability of the bacteria to import succinate or fumarate. Few transcriptional changes, with no obvious pattern, were detected. Overall, these data illustrated that succinate and fumarate are not essential for SNF and that, at least in specific symbioses,l-malate is likely the primary C4-dicarboxylate provided to the bacterium.IMPORTANCESymbiotic nitrogen fixation (SNF) is an economically and ecologically important biological process that allows plants to grow in nitrogen-poor soils without the need to apply nitrogen-based fertilizers. Much research has been dedicated to this topic to understand this process and to eventually manipulate it for agricultural gains. The work presented in this article provides new insights into the metabolic integration of the plant and bacterial partners. It is shown that malate is the only carbon source that needs to be available to the bacterium to support SNF and that, at least in some symbioses, malate, and not other C4-dicarboxylates, is likely the primary carbon provided to the bacterium. This work extends our knowledge of the minimal metabolic capabilities the bacterium requires to successfully perform SNF and may be useful in further studies aiming to optimize this process through synthetic biology approaches. The work describes an engineering approach to investigate a metabolic process that occurs between a eukaryotic host and its prokaryotic endosymbiont.

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Heterologous Complementation Reveals a Specialized Activity for BacA in the Medicago–Sinorhizobium meliloti Symbiosis

Molecular Plant-Microbe Interactions ◽

10.1094/mpmi-02-17-0030-r ◽

2017 ◽

Vol 30 (4) ◽

pp. 312-324 ◽

Cited By ~ 13

Author(s):

George C. diCenzo ◽

Maryam Zamani ◽

Hannah N. Ludwig ◽

Turlough M. Finan

Keyword(s):

Pisum Sativum ◽

Sinorhizobium Meliloti ◽

Rhizobium Leguminosarum ◽

Root Nodules ◽

Specific Interaction ◽

Model System ◽

Single Model ◽

Leguminous Plants ◽

Melilotus Alba ◽

Developmental Progression

The bacterium Sinorhizobium meliloti Rm2011 forms N2-fixing root nodules on alfalfa and other leguminous plants. The pSymB chromid contains a 110-kb region (the ETR region) showing high synteny to a chromosomally located region in Sinorhizobium fredii NGR234 and related rhizobia. We recently introduced the ETR region from S. fredii NGR234 into the S. meliloti chromosome. Here, we report that, unexpectedly, the S. fredii NGR234 ETR region did not complement deletion of the S. meliloti ETR region in symbiosis with Medicago sativa. This phenotype was due to the bacA gene of NGR234 not being functionally interchangeable with the S. meliloti bacA gene during M. sativa symbiosis. Further analysis revealed that, whereas bacA genes from S. fredii or Rhizobium leguminosarum bv. viciae 3841 failed to complement the Fix− phenotype of a S. meliloti bacA mutant with M. sativa, they allowed for further developmental progression prior to a loss of viability. In contrast, with Melilotus alba, bacA from S. fredii and R. leguminosarum supported N2 fixation by a S. meliloti bacA mutant. Additionally, the S. meliloti bacA gene can support N2 fixation of a R. leguminosarum bacA mutant during symbiosis with Pisum sativum. A phylogeny of BacA proteins illustrated that S. meliloti BacA has rapidly diverged from most rhizobia and has converged toward the sequence of pathogenic genera Brucella and Escherichia. These data suggest that the S. meliloti BacA has evolved toward a specific interaction with Medicago and highlights the limitations of using a single model system for the study of complex biological topics.

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Influence of Siduron and its Degradation Products on Soil Microflora

Weed Science ◽

10.1017/s0043174500047603 ◽

1968 ◽

Vol 16 (4) ◽

pp. 417-420 ◽

Cited By ~ 7

Author(s):

M. L. Fields ◽

D. D. Hemphill

Keyword(s):

Degradation Product ◽

Soil Bacteria ◽

Rhizobium Leguminosarum ◽

Degradation Products ◽

Streptomyces Griseus ◽

Soil Microflora ◽

Aspergillus Versicolor ◽

Rhizopus Nigricans ◽

Thiobacillus Thioparus ◽

Soil Ciliates

The herbicide l-(2-methylcyclohexyl)-3-phenylurea (siduron) suppressed the growth of soil bacteria,Azotobacter sp.andChlorella vulgariswhereas siduron had no effect on actinomycetes, filamentous fungi, soil ciliates and other algae. Siduron had no effect upon the growth ofThiobacillus thioparus, Euglena gracilis, andStreptomyces griseus.The degradation product, 2-methylcyclohexylamine (hereinafter referred to as 2-MCHA) suppressed the growth ofAztobacter chroococcumand soil ciliates. Aniline, another degradation product of siduron, depressed the growth ofAspergillus versicolorandA. fischeri;however,A. ochraceus, A. candidus, A. clavatus, A. nidulans, A. flavus, Botrytis cinerea, andRhizopus nigricanswere not affected. None of these fungi was influenced in growth by 2-MCHA.Streptomyces griseusgrew significantly less in the presence of aniline. The growth ofChlamydomonas pyrenoidosa, C. radiata, Anabaena catenula, andRhizobium leguminosarumwere not influenced by 10 ppm aniline or 10 ppm 2-MCHA.

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