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1.
Genome Announc ; 6(11)2018 Mar 15.
Article de Anglais | MEDLINE | ID: mdl-29545297

RÉSUMÉ

Here, we report the draft genome sequence of an isolate of Vibrio parahaemolyticus, VP14, recovered from the gut of Penaeus vannamei shrimp farmed in southern India. The genome of VP14 comprised 5,224,046 bp with a GC content of 45.3% and contained 5,326 genes, including 4,972 coding sequences.

2.
Virusdisease ; 27(2): 123-9, 2016 Jun.
Article de Anglais | MEDLINE | ID: mdl-27366762

RÉSUMÉ

Viral encephalopathy and retinopathy otherwise known as viral nervous necrosis (VNN) is a neuropathological condition affecting more than 50 fish species worldwide, mostly marine. Different PCR protocols with specific primers were reported from many countries for confirmation of VNN in fishes. In the present study, two pairs of primers were designed and evaluated for the diagnosis of clinical and subclinical cases of infections from field. These primers designated as BARL-F1/BARL-R1 amplified a 902 bp product in the variable region (T4) of the coat protein gene by first step PCR. Nested PCR primers BARL-F2/BARL-R2 amplified a fragment of 313 bp. The results were comparable with other commonly used primer sets such as F2/R3 and RG668f/RG919r primers. These new primers could detect betanodavirus in standard reference samples containing low, moderate and high viral load. Known positive and negative control samples of fish also revealed a predictive value of 100 % by RT-PCR diagnosis.

3.
Arch Virol ; 161(7): 2019-24, 2016 Jul.
Article de Anglais | MEDLINE | ID: mdl-27146046

RÉSUMÉ

This study was carried out to evaluate the efficiency of the Flinders Technology Associates (FTA(®)) card (Whatman(®)) as a sampling device and storage platform for RNA from betanodavirus-infected biological samples (viz., larvae, broodstock, cell culture supernatants and rearing seawater spiked with infected materials). The study showed that FTA cards can be used to detect betanodaviruses by reverse transcription-polymerase chain reaction (RT-PCR). The diagnostic efficiency of RT-PCR from all sample types on FTA cards decreased after 21 days of storage at 4 °C, although the virus could be detected up to 28 days by nested RT-PCR. The FTA card protocol thus provides a supplementary method for quick and easy collection of samples, preservation of RNA on a dry storage basis, and detection of betanodavirus-infected fish.


Sujet(s)
Maladies des poissons/virologie , Nodaviridae/isolement et purification , Infections à virus à ARN/médecine vétérinaire , RT-PCR/méthodes , Animaux , Maladies des poissons/diagnostic , Poissons , Nodaviridae/classification , Nodaviridae/génétique , Papier , Phylogenèse , Infections à virus à ARN/diagnostic , Infections à virus à ARN/virologie , ARN viral/génétique , RT-PCR/instrumentation
4.
Dis Aquat Organ ; 111(1): 23-9, 2014 Aug 21.
Article de Anglais | MEDLINE | ID: mdl-25144114

RÉSUMÉ

White spot syndrome virus (WSSV) replicates rapidly, can be extremely pathogenic and is a common cause of mass mortality in cultured shrimp. Variable number tandem repeat (VNTR) sequences present in the open reading frame (ORF)94, ORF125 and ORF75 regions of the WSSV genome have been used widely as genetic markers in epidemiological studies. However, reports that VNTRs might evolve rapidly following even a single transmission through penaeid shrimp or other crustacean hosts have created confusion as to how VNTR data is interpreted. To examine VNTR stability again, 2 WSSV strains (PmTN4RU and LvAP11RU) with differing ORF94 tandem repeat numbers and slight differences in apparent virulence were passaged sequentially 6 times through black tiger shrimp Penaeus monodon, Indian white shrimp Feneropenaeus indicus or Pacific white leg shrimp Litopenaeus vannamei. PCR analyses to genotype the ORF94, ORF125 and ORF75 VNTRs did not identify any differences from either of the 2 parental WSSV strains after multiple passages through any of the shrimp species. These data were confirmed by sequence analysis and indicate that the stability of the genome regions containing these VNTRs is quite high at least for the WSSV strains, hosts and number of passages examined and that the VNTR sequences thus represent useful genetic markers for studying WSSV epidemiology.


Sujet(s)
Instabilité du génome , Penaeidae/virologie , Virus de type 1 du syndrome des taches blanches/génétique , Animaux , Régulation de l'expression des gènes viraux , Interactions hôte-pathogène , Spécificité d'espèce , Facteurs temps , Virus de type 1 du syndrome des taches blanches/physiologie
5.
Acta Trop ; 135: 55-61, 2014 Jul.
Article de Anglais | MEDLINE | ID: mdl-24681224

RÉSUMÉ

An efficient and eco-friendly protocol for the synthesis of bioactive silver nanoparticles was developed using Naringi crenulata leaf extracts via microwave irradiation method. Silver nanoparticles were synthesized by treating N. crenulata leaf extracts with 1mM of aqueous silver nitrate solution. An effective bioactive compound such as alkaloids, phenols, saponins and quinines present in the N. crenulata reduces the Ag(+) into Ag(0). The synthesized silver nanoparticles were monitored by UV-vis spectrophotometer and further characterized by X-ray diffraction (XRD), Fourier Transform Infra Red (FTIR), Energy-dispersive X-ray spectroscopy (EDX) and field emission scanning electron microscopy (FESEM). UV-vis spectroscopy showed maximum absorbance at 390nm due to surface plasmon resonance of AgNPs. From FESEM results, an average crystal size of the synthesized nanoparticle was 72-98nm. FT-IR results showed sharp absorption peaks and they were assigned to phosphine, alkyl halides and sulfonate groups. Silver nanoparticles synthesized were generally found to be spherical and cubic shape. Topical application of ointment prepared from silver nanoparticles of N. crenulata were formulated and evaluated in vivo using the excision wound healing model on Wistar albino rats. The measurement of the wound areas was performed on 3rd, 6th, 9th, 12th and 15th days and the percentage of wound closures was calculated accordingly. By the 15th day, the ointment base containing 5% (w/w) of silver nanoparticles showed 100% wound healing activity compared with that of the reference as well as control bases. The results strongly suggested that the batch C ointment containing silver nanaoparticles synthesized from the leaf extracts of N. crenulata was found to be very effective in wound repair and encourages harnessing the potentials of the plant biomolecules loaded silver nanoparticle in the treatment of tropical diseases including wound healing.


Sujet(s)
Micro-ondes , Nanoparticules/usage thérapeutique , Extraits de plantes/usage thérapeutique , Argent/usage thérapeutique , Cicatrisation de plaie , Plaies et blessures/traitement médicamenteux , Administration par voie topique , Animaux , Modèles animaux de maladie humaine , Mâle , Microscopie électronique , Nanoparticules/ultrastructure , Extraits de plantes/isolement et purification , Rat Wistar , Rutaceae/composition chimique , Argent/analyse , Argent/isolement et purification , Spectrométrie d'émission X , Spectrophotométrie UV , Spectroscopie infrarouge à transformée de Fourier , Résultat thérapeutique , Diffraction des rayons X
6.
Virusdisease ; 25(1): 63-8, 2014 Jan.
Article de Anglais | MEDLINE | ID: mdl-24426311

RÉSUMÉ

Pacific white shrimp, Litopenaeus vannamei has been introduced recently for culture practice in India. Though SPF stocks are imported for larval production and thereafter culture practice, these are prone to infection with the existing viruses in the environment. Here we report mortality of L.vannamei in several farms in India with minimum biosecurity. The shrimp were harvested early within 50-72 days of culture due to the onset of disease and consequent mortality. As per the analysis carried out, the shrimp were infected with two virus, white spot syndrome virus (WSSV) and infectious hypodermal and hematopoietic necrosis virus (IHHNV). About 80 % of the samples collected had either or both of the viruses. A majority of these samples (60 %) had dual infection with WSSV and IHHNV. Infection of shrimp with WSSV and IHHNV could be detected both by PCR and histopathology. Some of the samples had either exclusively WSSV infection or IHHNV infection and were also harvested before the completion of the required culture period. All the samples analyzed were negative for taura syndrome virus, yellow head virus and infectious myonecrosis virus. While it is difficult to point out the exact etiological agent as the cause of mortality, strict biosecurity measures are advisable for the continuity of L. vannamei culture in India.

7.
J Bacteriol ; 195(17): 3797-807, 2013 Sep.
Article de Anglais | MEDLINE | ID: mdl-23772075

RÉSUMÉ

The thu operon (thuEFGKAB) in Sinorhizobium meliloti codes for transport and utilization functions of the disaccharide trehalose. Sequenced genomes of members of the Rhizobiaceae reveal that some rhizobia and Agrobacterium possess the entire thu operon in similar organizations and that Mesorhizobium loti MAFF303099 lacks the transport (thuEFGK) genes. In this study, we show that this operon is dedicated to the transport and assimilation of maltitol and isomers of sucrose (leucrose, palatinose, and trehalulose) in addition to trehalulose, not only in S. meliloti but also in Agrobacterium tumefaciens. By using genetic complementation, we show that the thuAB genes of S. meliloti, M. loti, and A. tumefaciens are functionally equivalent. Further, we provide both genetic and biochemical evidence to show that these bacteria assimilate these disaccharides by converting them to their respective 3-keto derivatives and that the thuAB genes code for this ketodisaccharide-forming enzyme(s). Formation of 3-ketotrehalose in real time in live S. meliloti is shown through Raman spectroscopy. The presence of an additional ketodisaccharide-forming pathway(s) in A. tumefaciens is also indicated. To our knowledge, this is the first report to identify the genes that code for the conversion of disaccharides to their 3-ketodisaccharide derivatives in any organism.


Sujet(s)
Agrobacterium tumefaciens/métabolisme , Maltose/analogues et dérivés , Opéron , Sinorhizobium meliloti/métabolisme , Saccharose/métabolisme , Polyols/métabolisme , Tréhalose/métabolisme , Agrobacterium tumefaciens/composition chimique , Agrobacterium tumefaciens/génétique , Transport biologique , Biotransformation , Test de complémentation , Maltose/métabolisme , Voies et réseaux métaboliques/génétique , Sinorhizobium meliloti/composition chimique , Sinorhizobium meliloti/génétique , Analyse spectrale Raman
8.
New Phytol ; 179(2): 495-504, 2008 Jul.
Article de Anglais | MEDLINE | ID: mdl-19086182

RÉSUMÉ

The role of host and bacterial genotypes in determining the competitiveness of trehalose utilization mutants of Sinorhizobium meliloti and Sinorhizobium medicae was investigated here. Trehalose utilization mutants of S. meliloti and S. medicae were obtained by mutagenesis of their trehalose utilization gene thuB. The mutant strains and the wild type were coinoculated on three cultivars of alfalfa (Medicago sativa) and two cultivars of Medicago truncatula and assessed for competitiveness in root colonization, and nodule occupancy. The thuB mutants formed more nodules than their parent strains on two of the three alfalfa lines tested and on one of the two M. truncatula lines tested. They were not more competitive on the other alfalfa and M. truncatula lines. Their competitiveness for nodule occupancy did not correlate positively with their ability to colonize these roots but correlated with the extent of thuB induction in the infection threads. Induction of thuB was shown to be dependent on the concentration of trehalose in the environment. These results suggest a direct role for host trehalose metabolism in early plant-symbiont interactions and show that the ability to manage host-induced stresses during infection, rather than the ability to colonize the root, is critical for competitive nodulation.


Sujet(s)
Medicago sativa/génétique , Medicago truncatula/génétique , Nodulation racinaire/physiologie , Sinorhizobium/métabolisme , Tréhalose/métabolisme , Relation dose-effet des médicaments , Protéines fongiques/génétique , Protéines fongiques/métabolisme , Régulation de l'expression des gènes fongiques/physiologie , Génotype , Medicago sativa/classification , Medicago sativa/microbiologie , Medicago truncatula/classification , Medicago truncatula/microbiologie , Concentration osmolaire , Stress oxydatif , Sinorhizobium/effets des médicaments et des substances chimiques , Sinorhizobium/génétique , Tréhalose/pharmacologie , beta-Galactosidase/métabolisme
9.
Mol Plant Microbe Interact ; 18(7): 694-702, 2005 Jul.
Article de Anglais | MEDLINE | ID: mdl-16042015

RÉSUMÉ

Genes thuA and thuB in Sinorhizobium meliloti Rm1021 code for a major pathway for trehalose catabolism and are induced by trehalose but not by related structurally similar disaccharides like sucrose or maltose. S. meliloti strains mutated in either of these two genes were severely impaired in their ability to grow on trehalose as the sole source of carbon. ThuA and ThuB show no homology to any known enzymes in trehalose utilization. ThuA has similarity to proteins of unknown function in Mesorhizobium loti, Agrobacterium tumefaciens, and Brucella melitensis, and ThuB possesses homology to dehydrogenases containing the consensus motif AGKHVXCEKP. thuAB genes are expressed in bacteria growing on the root surface and in the infection threads but not in the symbiotic zone of the nodules. Even though thuA and thuB mutants were impaired in competitive colonization of Medicago sativa roots, these strains were more competitive than the wild-type Rml021 in infecting alfalfa roots and forming nitrogen-fixing nodules. Possible reasons for their increased competitiveness are discussed.


Sujet(s)
Medicago sativa/métabolisme , Medicago sativa/microbiologie , Sinorhizobium meliloti/métabolisme , Tréhalose/métabolisme , Protéines bactériennes/génétique , Protéines bactériennes/métabolisme , Séquence nucléotidique , Transport biologique actif , ADN bactérien/génétique , Gènes bactériens , Test de complémentation , Données de séquences moléculaires , Mutation , Racines de plante/microbiologie , Sinorhizobium meliloti/génétique , Symbiose
10.
Environ Microbiol ; 7(7): 1049-58, 2005 Jul.
Article de Anglais | MEDLINE | ID: mdl-15946302

RÉSUMÉ

The symbiotic and saprophytic persistence of three unmarked Rhizobium leguminosarum biovar trifolii (Rlt) strains introduced into a field site in Iceland were followed. This site was free of clover cultivation and initially devoid of clover-nodulating rhizobia as tested by nodulation studies. Nodule occupancy by strains was identified based on their distinct ERIC-polymerase chain reaction (PCR) DNA fingerprint patterns. The survival and persistence of the individual strains in soil were monitored by the quantitative real-time PCR (qRT-PCR) assay, targeting the host-specific nodE gene. The most dominant strain in the nodule population, Rlt 20-15, showed relatively less saprophytic survival ability and maintained high numbers only in the presence of the appropriate host plant. Conversely, the minor nodule occupant, Rlt 32-28, persisted in soil at a relatively higher abundance both in the presence of its host legumes and in the presence of a non-host grass. The qRT-PCR assay was successfully applied to quantify rhizobial strains directly in soil without culturing or nodulation. However, the assay demonstrated less sensitivity compared with the plant infection most-probable-number (MPN) method for estimating the population size of rhizobia in soil. The quantitative detection limit of our qRT-PCR assays was 1 x 10(3) cells per gram of soil, as opposed to the MPN test which has a detection limit of 10 cells per gram of soil.


Sujet(s)
Acyltransferases/génétique , Protéines bactériennes/génétique , Medicago/microbiologie , Protéines membranaires/génétique , Rhizobium leguminosarum/croissance et développement , Microbiologie du sol , Symbiose , Numération de colonies microbiennes , ADN bactérien/analyse , ADN bactérien/isolement et purification , Fixation de l'azote , Racines de plante/microbiologie , RT-PCR , Rhizobium leguminosarum/classification , Rhizobium leguminosarum/génétique
11.
Plant Physiol ; 136(1): 2887-94, 2004 Sep.
Article de Anglais | MEDLINE | ID: mdl-15347793

RÉSUMÉ

Plants naturally cycle amino acids across root cell plasma membranes, and any net efflux is termed exudation. The dominant ecological view is that microorganisms and roots passively compete for amino acids in the soil solution, yet the innate capacity of roots to recover amino acids present in ecologically relevant concentrations is unknown. We find that, in the absence of culturable microorganisms, the influx rates of 16 amino acids (each supplied at 2.5 microm) exceed efflux rates by 5% to 545% in roots of alfalfa (Medicago sativa), Medicago truncatula, maize (Zea mays), and wheat (Triticum aestivum). Several microbial products, which are produced by common soil microorganisms such as Pseudomonas bacteria and Fusarium fungi, significantly enhanced the net efflux (i.e. exudation) of amino acids from roots of these four plant species. In alfalfa, treating roots with 200 microm phenazine, 2,4-diacetylphloroglucinol, or zearalenone increased total net efflux of 16 amino acids 200% to 2,600% in 3 h. Data from (15)N tests suggest that 2,4-diacetylphloroglucinol blocks amino acid uptake, whereas zearalenone enhances efflux. Thus, amino acid exudation under normal conditions is a phenomenon that probably reflects both active manipulation and passive uptake by microorganisms, as well as diffusion and adsorption to soil, all of which help overcome the innate capacity of plant roots to reabsorb amino acids. The importance of identifying potential enhancers of root exudation lies in understanding that such compounds may represent regulatory linkages between the larger soil food web and the internal carbon metabolism of the plant.


Sujet(s)
Acides aminés/métabolisme , Plantes/métabolisme , Plantes/microbiologie , Transport biologique actif/effets des médicaments et des substances chimiques , Fusarium/métabolisme , Cinétique , Medicago sativa/métabolisme , Medicago sativa/microbiologie , Medicago truncatula/métabolisme , Medicago truncatula/microbiologie , Phénazines/pharmacologie , Phloroglucinol/analogues et dérivés , Phloroglucinol/pharmacologie , Racines de plante/effets des médicaments et des substances chimiques , Racines de plante/métabolisme , Racines de plante/microbiologie , Pseudomonas/métabolisme , Microbiologie du sol , Symbiose , Triticum/métabolisme , Triticum/microbiologie , Zea mays/métabolisme , Zea mays/microbiologie , Zéaralénone/pharmacologie
12.
J Bacteriol ; 184(11): 2978-86, 2002 Jun.
Article de Anglais | MEDLINE | ID: mdl-12003938

RÉSUMÉ

We have identified a cluster of six genes involved in trehalose transport and utilization (thu) in Sinorhizobium meliloti. Four of these genes, thuE, -F, -G, and -K, were found to encode components of a binding protein-dependent trehalose/maltose/sucrose ABC transporter. Their deduced gene products comprise a trehalose/maltose-binding protein (ThuE), two integral membrane proteins (ThuF and ThuG), and an ATP-binding protein (ThuK). In addition, a putative regulatory protein (ThuR) was found divergently transcribed from the thuEFGK operon. When the thuE locus was inactivated by gene replacement, the resulting S. meliloti strain was impaired in its ability to grow on trehalose, and a significant retardation in growth was seen on maltose as well. The wild type and the thuE mutant were indistinguishable for growth on glucose and sucrose. This suggested a possible overlap in function of the thuEFGK operon with the aglEFGAK operon, which was identified as a binding protein-dependent ATP-binding transport system for sucrose, maltose, and trehalose. The K(m)s for trehalose transport were 8 +/- 1 nM and 55 +/- 5 nM in the uninduced and induced cultures, respectively. Transport and growth experiments using mutants impaired in either or both of these transport systems show that these systems form the major transport systems for trehalose, maltose, and sucrose. By using a thuE'-lacZ fusion, we show that thuE is induced only by trehalose and not by cellobiose, glucose, maltopentaose, maltose, mannitol, or sucrose, suggesting that the thuEFGK system is primarily targeted toward trehalose. The aglEFGAK operon, on the other hand, is induced primarily by sucrose and to a lesser extent by trehalose. Tests for root colonization, nodulation, and nitrogen fixation suggest that uptake of disaccharides can be critical for colonization of alfalfa roots but is not important for nodulation and nitrogen fixation per se.


Sujet(s)
Transport biologique/génétique , Maltose/métabolisme , Opéron , Sinorhizobium meliloti/génétique , Saccharose/métabolisme , Tréhalose/métabolisme , Transporteurs ABC/génétique , Milieux de culture , Gènes bactériens , Glucose , Medicago sativa/microbiologie , Données de séquences moléculaires , Mutagenèse par insertion , Sinorhizobium meliloti/croissance et développement , Sinorhizobium meliloti/métabolisme
13.
Mol Plant Microbe Interact ; 15(5): 456-62, 2002 May.
Article de Anglais | MEDLINE | ID: mdl-12036276

RÉSUMÉ

Genes contributing to riboflavin production in Sinorhizobium meliloti were identified, and bacterial strains that overproduce this vitamin were constructed to characterize how additional riboflavin affects interactions between alfalfa (Medicago sativa) and S. meliloti. Riboflavin-synthesis genes in S. meliloti were found in three separate linkage groups and designated as ribBA, ribDribC, and ribH for their similarities to Escherichia coli genes. The ribBA and ribC loci complemented corresponding E. coli rib mutants. S. meliloti cells containing extra copies of ribBA released 10 to 20% more riboflavin than a control strain but grew at similar rates in a defined medium lacking riboflavin. Cells carrying extra copies of ribBA colonized roots to densities that were 55% higher than that of a control strain. No effect of extra rib genes was detected on alfalfa grown in the absence or presence of combined N. These results support the importance of extracellular riboflavin for alfalfa root colonization by S. meliloti and are consistent with the hypothesis that this molecule benefits bacteria indirectly through an effect on the plant.


Sujet(s)
GTP cyclohydrolase I/génétique , Intramolecular transferases/génétique , Medicago sativa/physiologie , Riboflavine synthase/génétique , Riboflavine/biosynthèse , Sinorhizobium/physiologie , Symbiose/physiologie , Séquence d'acides aminés , Protéines bactériennes/génétique , Protéines bactériennes/physiologie , GTP cyclohydrolase I/physiologie , Intramolecular transferases/physiologie , Medicago sativa/microbiologie , Données de séquences moléculaires , Racines de plante/microbiologie , Racines de plante/physiologie , Riboflavine/physiologie , Riboflavine synthase/physiologie , Similitude de séquences d'acides aminés , Sinorhizobium/génétique , Symbiose/génétique
14.
Proc Natl Acad Sci U S A ; 86(4): 1244-8, 1989 Feb.
Article de Anglais | MEDLINE | ID: mdl-16594017

RÉSUMÉ

Rhizobium nod genes are essential for root hair deformation and cortical cell division, early stages in the development of nitrogen-fixing root nodules. Nod(-) mutants are unable to initiate nodules on legume roots. We observed that N-(1-naphthyl)phthalamic acid and 2,3,5-triiodobenzoic acid, compounds known to function as auxin transport inhibitors, induced nodule-like structures on alfalfa roots. The nodule-like structures (pseudonodules) were white, devoid of bacteria, and resembled nodules elicited by Rhizobium meliloti exopolysaccharide (exo) mutants at both the histological and molecular level. Two nodulin genes, ENOD2 and Nms-30, were expressed. RNA isolated from the nodule-like structures hybridized to pGmENOD2, a soybean early nodulin cDNA clone. RNA isolated from roots did not hybridize. We determined by in vitro translations of total RNA that the alfalfa nodulin transcript Nms-30 was also expressed in the nodule-like structures. The late expressed nodulin genes, such as the leghemoglobin genes, were not transcribed. Because N-(1-naphthyl)phthalamic acid and 2,3,5-triiodobenzoic acid induce the development of nodules on alfalfa roots, we suggest that the auxin transport inhibitors mimic the activity of compound(s) made upon the induction of the Rhizobium nod genes.

15.
Plant Mol Biol ; 12(2): 157-67, 1989 Feb.
Article de Anglais | MEDLINE | ID: mdl-24272795

RÉSUMÉ

The mRNA population in pea root hairs was characterized by means of in vitro translation of total root hair RNA followed by 2-dimensional gel electrophoresis of the translation products. Root hairs contain several mRNAs not detectable in total RNA preparations from roots. Most of these root hair-specific mRNAs occur in elongating root hairs at higher levels than in mature root hairs. The expression of some genes in pea root hairs is typically affected by inoculation with Rhizobium leguminosarum. One gene, encoding RH-42, is specifically induced while the expression of another gene, encoding RH-44, is markedly enhanced. Using R. leguminosarum mutants it was shown that the nodC gene is required for the induction and enhancement of expression of the RH-42 and RH-44 genes, respectively, while the Rhizobium chromosomal gene pss1, involved in exopolysaccharide synthesis, is not essential. After induction of the nod genes with apigenin the bacteria excrete into the culture medium a factor that causes root hair deformation. This deformation factor stimulates the expression of the RH-44 gene but does not induce the expression of the gene encoding RH-42.

16.
Plant Physiol ; 86(4): 1210-5, 1988 Apr.
Article de Anglais | MEDLINE | ID: mdl-16666056

RÉSUMÉ

When serial dilutions of a suspension of Bradyrhizobium japonicum strain 138 were inoculated onto both soybean and cowpea roots, the formation of nodules in the initially susceptible region of the roots of both hosts was found to be linearly dependent on the log of the inoculum dosage until an optimum dosage was reached. Approximately 30- to 100-fold higher dosages were required to elicit half-maximal nodulation on cowpea than on soybean in the initially susceptible zone of the root. However, at optimal dosages, about six times as many nodules formed in this region on cowpea roots than on soybean roots. There was no appreciable difference in the apparent rate of nodule initiation on these two hosts nor in the number of inoculum bacteria in contact with the root. These results are consistent with the possibility that cowpea roots have a substantially higher threshold of response to symbiotic signals from the bacteria than do soybean roots. Storage of B. japonicum cells in distilled water for several weeks did not affect their viability or efficiency of nodule initiation on soybean. However, the nodulation efficiency of these same cells on cowpea diminished markedly over a 2 week period. These differential effects of water storage indicate that at least some aspects of signal production by the bacteria during nodule initiation are different on the two hosts. Mutants of B. japonicum 138 defective in synthesis of soybean lectin binding polysaccharide were defective in their efficiency of nodule initiation on soybean but not on cowpea. These results also suggest that B. japonicum may produce different substances to initiate nodules on these two hosts.

17.
J Bacteriol ; 153(1): 443-51, 1983 Jan.
Article de Anglais | MEDLINE | ID: mdl-6681538

RÉSUMÉ

The infectivity of the soybean symbiont Rhizobium japonicum changed two- to fivefold with culture age for strains 110 ARS, 138 Str Spc, and 123 Spc, whereas culture age had relatively little effect on the infectivity of strains 83 Str and 61A76 Str. Infectivity was measured by determining the number of nodules which developed on soybean primary roots in the zone which contained developing and preemergent root hairs at the time of inoculation. Root cells in this region of the host root are susceptible to Rhizobium infection, but this susceptibility is lost during acropetal development and maturation of the root cells within a period of 4 to 6 h (T. V. Bhuvaneswari, B. G. Turgeon, and W. D. Bauer, Plant Physiol. 66:1027-1031, 1980). Profiles of nodulation frequency at different locations on the root were not affected by the age of the R. japonicum cultures, indicating that culture age affected the efficiency of Rhizobium infection rather than how soon infections were initiated after inoculation. Inoculum dose-response experiments also indicated that culture age affected the efficiency of infection. Two strains, 61A76 Str and 83 Str, were relatively inefficient at all culture ages, particularly at low inoculum doses. Changes in infectivity with culture age were reasonably well correlated with changes in the proportion of cells in a culture capable of binding soybean lectin. Suspensions of R. japonicum in water were found to retain their viability and infectivity.


Sujet(s)
Glycine max/microbiologie , Rhizobium/croissance et développement , Protéines de soja , Symbiose , Antibactériens/pharmacologie , Résistance microbienne aux médicaments , Lectines , Mutation , Lectines végétales , Rhizobium/métabolisme , Facteurs temps
18.
Plant Physiol ; 68(5): 1144-9, 1981 Nov.
Article de Anglais | MEDLINE | ID: mdl-16662065

RÉSUMÉ

Root cells of four common legumes were found to remain susceptible to nodulation by rhizobia for only a short period of time. Delayed inoculation experiments conducted with these legume hosts indicated that the initially susceptible region of the root became progressively less susceptible if inoculations were delayed by a few hours. Profiles of the frequency of nodule formation relative to marks indicating the regions of root and root hair development at the time of inoculation indicated that nodulation of Vigna sinensis (L.) Endl. cv California Black Eye and Medicago sativa L. cvs Moapa and Vernal roots was inhibited just below the region that was most susceptible at the time of inoculation. This result suggests the existence of a fast-acting regulatory mechanism in these hosts that prevents overnodulation. Nodulation in white clover may occur in two distinct phases. In addition to the transient susceptibility of preemergent and developing root hair cells, there appeared to be an induced susceptibility of mature clover root hair cells. A cell-free bacterial exudate preparation from Rhizobium trifolii cells was found to render mature root hair cells of white clover more rapidly susceptible to nodulation.

19.
Plant Physiol ; 66(6): 1027-31, 1980 Dec.
Article de Anglais | MEDLINE | ID: mdl-16661570

RÉSUMÉ

The infectible cells of soybean roots appear to be located at any given time just above the zone of root elongation and just below the position of the smallest emergent root hairs. The location of infectible cells on the primary root at the time of inoculation was inferred from the position of subsequent nodule development, correcting for displacement of epidermal cells due to root elongation. Marks were made on the seedling growth pouches at the time of inoculation to indicate the position of the root tip and the zones of root hair development. Virtually all of the seedlings developed nodules on the primary root above the marks made at the root tips at the time of inoculation. None of the plants formed nodules on the root where mature root hairs were present at the time of inoculation. These results and profiles of nodulation frequency indicate that the location of infectible cells is developmentally restricted. When inoculations were delayed for intervals of 1 to 4 hours after marking the positions of the root tips, progressively fewer nodules were formed above the root tip marks, and the uppermost of these nodules were formed at progressively shorter distances above the marks. These results indicate that the infectibility of given host cells is a transient property that appears and then is lost within a few hours. The results also indicate that host responses leading to infection and nodulation are triggered or initiated in less than 2 hours after inoculation. The extent of nodulation above the root tip mark increased in proportion to the logarithm of the number of bacteria in the inoculum.

20.
Plant Physiol ; 62(1): 71-4, 1978 Jul.
Article de Anglais | MEDLINE | ID: mdl-16660472

RÉSUMÉ

The influence of rhizosphere/rhizoplane culture conditions on the ability of various rhizobia to bind soybean seed lectin (SBL) was examined. Eleven strains of the soybean symbiont, Rhizobium japonicum, and six strains of various heterologous Rhizobium species were cultured in root exudate of soybean (Glycine max [L.] Merr.) and in association with roots of soybean seedlings which were growing either hydroponically or in montmorillonite clay soil amendment (Turface). All 11 of the R. japonicum strains developed biochemically specific receptors for the lectin when cultured under these conditions, whereas six of the 11 did not develop such receptors when cultured in synthetic salts medium. Two cowpea strains also developed receptors for SBL. The other four heterologous strains of rhizobia gave no evidence of biochemically specific SBL binding in either synthetic salts media or rhizosphere/rhizoplane cultures. These results demonstrate that the environment provided by plant roots is an important factor in the development of specific lectin receptors on the cell surface of R. japonicum.

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