scholarly journals Mutation of rpiA in Enterobacter cloacae Decreases Seed and Root Colonization and Biocontrol of Damping-Off Caused by Pythium ultimum on Cucumber

2002 ◽  
Vol 15 (8) ◽  
pp. 817-825 ◽  
Author(s):  
Scott M. Lohrke ◽  
Pierre D. Dery ◽  
Wei Li ◽  
Ralph Reedy ◽  
Donald Y. Kobayashi ◽  
...  
Keyword(s):  
Pentose Phosphate Pathway ◽  
Sequence Similarity ◽  
Enterobacter Cloacae ◽  
Pythium Ultimum ◽  
Pentose Phosphate ◽  
Disease Suppression ◽  
Amino Acid Sequence Similarity ◽  
Damping Off ◽  
Isomerase Activity ◽  
Key Enzyme

Strains of Enterobacter cloacae show promise as biocontrol agents for Pythium ultimum-induced damping-off on cucumber and other crops. E. cloacae A145 is a mini-Tn5 Km transposon mutant of strain 501R3 that was significantly reduced in suppression of damping-off on cucumber caused by P. ultimum. Strain A145 was deficient in colonization of cucumber, sunflower, and wheat seeds and significantly reduced in colonization of corn and cowpea seeds relative to strain 501R3. Populations of strain A145 were also significantly lower than those of strain 501R3 at all sampling times in cucumber, wheat, and sunflower rhizosphere. Populations of strain A145 were not detectable in any rhizosphere after 42 days, while populations of strain 501R3 remained at substantial levels throughout all experiments. Molecular characterization of strain A145 indicated mini-Tn5 Km was inserted in a region of the E. cloacae genome with a high degree of DNA and amino acid sequence similarity to rpiA, which encodes ribose-5-phosphate isomerase. In Escherichia coli, RpiA catalyzes the interconversion of ribose-5-phosphate and ribulose-5-phosphate and is a key enzyme in the pentose phosphate pathway. Ribose-5-phosphate isomerase activity in cell lysates from strain A145 was approximately 3.5% of that from strain 501R3. In addition, strain A145 was a ribose auxotroph, as expected for an rpiA mutant. Introduction of a 1.0-kb DNA fragment containing only the rpiA homologue into strain A145 restored ribose phosphate isomerase activity, prototrophy, seedling colonization, and disease suppression to levels similar to those associated with strain 501R3. Experiments reported here indicate a key role for rpiA and possibly the pentose phosphate pathway in suppression of damping-off and colonization of subterranean portions of plants by E. cloacae.

scholarly journals Mutation of a degS Homologue in Enterobacter cloacae Decreases Colonization and Biological Control of Damping-Off on Cucumber

2011 ◽  
Vol 101 (2) ◽  
pp. 271-280 ◽  
Author(s):  
Daniel P. Roberts ◽  
Scott M. Lohrke ◽  
Laurie McKenna ◽  
Dilip K. Lakshman ◽  
Hyesuk Kong ◽  
...  
Keyword(s):  
Stress Response ◽  
Enterobacter Cloacae ◽  
Pythium Ultimum ◽  
Damping Off ◽  
E Coli ◽  
Transposon Insertion ◽  
Acidic Conditions ◽  
And Control ◽  
First Time ◽  
Reducing Stress

We have been using mutagenesis to determine how biocontrol bacteria such as Enterobacter cloacae 501R3 deal with complex nutritional environments found in association with plants. E. cloacae C10, a mutant of 501R3 with a transposon insertion in degS, was diminished in growth on synthetic cucumber root exudate (SRE), colonization of cucumber seed and roots, and control of damping-off of cucumber caused by Pythium ultimum. DegS, a periplasmic serine protease in the closely related bacterium Escherichia coli K12, is required for the RpoE-mediated stress response. C10 containing wild-type degS from 501R3 or from E. coli K12 on pBeloBAC11 was significantly increased in growth on SRE, colonization of cucumber roots, and control of P. ultimum relative to C10 containing pBeloBAC11 alone. C10 and 501R3 were similar in sensitivity to acidic conditions, plant-derived phenolic compounds, oxidative stress caused by hydrogen peroxide, dessication, and high osmoticum; stress conditions potentially associated with plants. This study demonstrates a role for degS in the spermosphere and rhizosphere during colonization and disease control by Enterobacter cloacae. This study implicates, for the first time, the involvement of DegS and, by extension, the RpoE-mediated stress response, in reducing stress on E. cloacae resulting from the complex nutritional environments in the spermosphere and rhizosphere.

The 2, 4-dichlorophenol hydroxylase ofAlcaligenes eutrophusJMP134 is a homotetramer

1997 ◽  
Vol 43 (2) ◽  
pp. 202-205 ◽  
Author(s):  
Lulu Farhana ◽  
Peter B. New
Keyword(s):  
Sequence Similarity ◽  
Affinity Purification ◽  
Alcaligenes Eutrophus ◽  
Exchange Chromatography ◽  
Single Type ◽  
Amino Acid Sequence Similarity ◽  
Dichlorophenoxyacetic Acid ◽  
Enzyme Preparations ◽  
Native Molecular Mass ◽  
Key Enzyme

2, 4-Dichlorophenol hydroxylase (DCP-hydroxylase) is a key enzyme in the pathway for degradation of 2, 4-dichlorophenoxyacetic acid (2, 4-D) in many bacteria. In Alcaligenes eutrophus JMP134, DCP-hydroxylase was reported to consist of two dissimilar types of subunit of 66 and 45 kDa, a structure which is different from that in other bacteria. Using a different procedure involving affinity purification and ion-exchange chromatography, we have purified active enzyme from JMP134 and show that it has a native molecular mass of approximately 245 kDa and consists of a single type of subunit of 66 kDa, similar to all other flavoprotein monooxygenase enzymes. A 45-kDa polypeptide, found in partially purified enzyme preparations, was not required for enzyme activity but had some serologic and N-terminal amino acid sequence similarity to the 66-kDa enzyme subunit.Key words: 2, 4-dichlorophenol hydroxylase, Alcaligenes eutrophus, 2, 4-D biodegradation.

Increased participation of pentose phosphate pathway in response to afterripening and gibberellic acid treatment in caryopses of Avena fatua

1971 ◽  
Vol 49 (10) ◽  
pp. 1833-1840 ◽  
Author(s):  
J. A. Simmonds ◽  
G. M. Simpson
Keyword(s):  
Oxygen Consumption ◽  
Gibberellic Acid ◽  
Pentose Phosphate Pathway ◽  
Qualitative Change ◽  
Pentose Phosphate ◽  
Avena Fatua ◽  
Starch Degradation ◽  
Phosphogluconate Dehydrogenase ◽  
Key Enzyme ◽  
Excised Embryos

The rates of oxygen consumption of dormant and non-dormant excised embryos of Avena fatua L. before germination are similar. Gibberellic acid (GA) treatment stimulates germination of dormant embryos without affecting oxygen consumption. Thus dormancy is not the result of restricted oxygen uptake. The fat content of dormant and non-dormant caryopses remains constant during germination. Dormant and non-dormant embryos have respiratory quotients near unity supporting the hypothesis that starch degradation occurs before germination. 6-Phosphogluconate dehydrogenase, a key enzyme of the pentose phosphate pathway, is present in dormant and non-dormant dry embryos but the pre-germination C6/C1 ratio of non-dormant embryos is markedly lower than that of dormant embryos, indicating a greater participation of the pentose phosphate pathway in the respiratory metabolism of non-dormant embryos. Release from dormancy is associated with a shift in metabolism from the glycolytic pathway to the pentose phosphate pathway. GA treatment, which stimulates germination of dormant embryos, causes a similar qualitative change in the oxidative metabolism of dormant embryos. Thus the action of GA is to cause the increased degradation of glucose via the pentose phosphate pathway, which is an essential step in the preparation for germination.

scholarly journals The Pentose Phosphate Pathway in Yeasts–More Than a Poor Cousin of Glycolysis

Biomolecules ◽  
2021 ◽  
Vol 11 (5) ◽  
pp. 725
Author(s):  
Laura-Katharina Bertels ◽  
Lucía Fernández Murillo ◽  
Jürgen J. Heinisch
Keyword(s):  
Pentose Phosphate Pathway ◽  
Kluyveromyces Lactis ◽  
Aromatic Amino Acids ◽  
Pentose Phosphate ◽  
Minor Role ◽  
Disease Genes ◽  
Yeast Saccharomyces Cerevisiae ◽  
Key Enzyme ◽  
A Minor ◽  
Glucose 6 Phosphate Dehydrogenase

The pentose phosphate pathway (PPP) is a route that can work in parallel to glycolysis in glucose degradation in most living cells. It has a unidirectional oxidative part with glucose-6-phosphate dehydrogenase as a key enzyme generating NADPH, and a non-oxidative part involving the reversible transketolase and transaldolase reactions, which interchange PPP metabolites with glycolysis. While the oxidative branch is vital to cope with oxidative stress, the non-oxidative branch provides precursors for the synthesis of nucleic, fatty and aromatic amino acids. For glucose catabolism in the baker’s yeast Saccharomyces cerevisiae, where its components were first discovered and extensively studied, the PPP plays only a minor role. In contrast, PPP and glycolysis contribute almost equally to glucose degradation in other yeasts. We here summarize the data available for the PPP enzymes focusing on S. cerevisiae and Kluyveromyces lactis, and describe the phenotypes of gene deletions and the benefits of their overproduction and modification. Reference to other yeasts and to the importance of the PPP in their biotechnological and medical applications is briefly being included. We propose future studies on the PPP in K. lactis to be of special interest for basic science and as a host for the expression of human disease genes.

scholarly journals Fatty Acid Competition as a Mechanism by Which Enterobacter cloacae Suppresses Pythium ultimum Sporangium Germination and Damping-Off

2000 ◽  
Vol 66 (12) ◽  
pp. 5340-5347 ◽  
Author(s):  
Karin van Dijk ◽  
Eric B. Nelson
Keyword(s):  
Fatty Acids ◽  
Biological Control ◽  
Fatty Acid ◽  
Linoleic Acid ◽  
Plant Pathogens ◽  
Enterobacter Cloacae ◽  
Pythium Ultimum ◽  
Plant Diseases ◽  
Disease Suppression ◽  
Acid Uptake

ABSTRACT Interactions between plant-associated microorganisms play important roles in suppressing plant diseases and enhancing plant growth and development. While competition between plant-associated bacteria and plant pathogens has long been thought to be an important means of suppressing plant diseases microbiologically, unequivocal evidence supporting such a mechanism has been lacking. We present evidence here that competition for plant-derived unsaturated long-chain fatty acids between the biological control bacterium Enterobacter cloacae and the seed-rotting oomycete, Pythium ultimum, results in disease suppression. Since fatty acids from seeds and roots are required to elicit germination responses ofP. ultimum, we generated mutants of E. cloacaeto evaluate the role of E. cloacae fatty acid metabolism on the suppression of Pythium sporangium germination and subsequent plant infection. Two mutants of E. cloacaeEcCT-501R3, Ec31 (fadB) and EcL1 (fadL), were reduced in β-oxidation and fatty acid uptake, respectively. Both strains failed to metabolize linoleic acid, to inactivate the germination-stimulating activity of cottonseed exudate and linoleic acid, and to suppress Pythium seed rot in cotton seedling bioassays. Subclones containing fadBA or fadLcomplemented each of these phenotypes in Ec31 and EcL1, respectively. These data provide strong evidence for a competitive exclusion mechanism for the biological control of P. ultimum-incited seed infections by E. cloacae where E. cloacaeprevents the germination of P. ultimum sporangia by the efficient metabolism of fatty acid components of seed exudate and thus prevents seed infections.

scholarly journals Compost-Induced Suppression of Pythium Damping-Off Is Mediated by Fatty-Acid-Metabolizing Seed-Colonizing Microbial Communities

2003 ◽  
Vol 69 (1) ◽  
pp. 452-460 ◽  
Author(s):  
Mary E. McKellar ◽  
Eric B. Nelson
Keyword(s):  
Fatty Acid ◽  
Linoleic Acid ◽  
Microbial Communities ◽  
Pythium Ultimum ◽  
Disease Suppression ◽  
Microbial Consortia ◽  
Damping Off ◽  
Bacterial Consortia ◽  
Seed Colonization

ABSTRACT Leaf composts were studied for their suppressive effects on Pythium ultimum sporangium germination, cottonseed colonization, and the severity of Pythium damping-off of cotton. A focus of the work was to assess the role of fatty-acid-metabolizing microbial communities in disease suppression. Suppressiveness was expressed within the first few hours of seed germination as revealed by reduced P. ultimum sporangium germination, reduced seed colonization, and reduced damping-off in transplant experiments. These reductions were not observed when cottonseeds were sown in a conducive leaf compost. Microbial consortia recovered from the surface of cottonseeds during the first few hours of germination in suppressive compost (suppressive consortia) induced significant levels of damping-off suppression, whereas no suppression was induced by microbial consortia recovered from cottonseeds germinated in conducive compost (conducive consortia). Suppressive consortia rapidly metabolized linoleic acid, whereas conducive consortia did not. Furthermore, populations of fatty-acid-metabolizing bacteria and actinobacteria were higher in suppressive consortia than in conducive consortia. Individual bacterial isolates varied in their ability to metabolize linoleic acid and protect seedlings from damping-off. Results indicate that communities of compost-inhabiting microorganisms colonizing cottonseeds within the first few hours after sowing in a Pythium-suppressive compost play a major role in the suppression of P. ultimum sporangium germination, seed colonization, and damping-off. Results further indicate that fatty acid metabolism by these seed-colonizing bacterial consortia can explain the Pythium suppression observed.

scholarly journals Compost Tea as a Container Medium Drench for Suppressing Seedling Damping-Off Caused by Pythium ultimum

2004 ◽  
Vol 94 (11) ◽  
pp. 1156-1163 ◽  
Author(s):  
Steven J. Scheuerell ◽  
Walter F. Mahaffee
Keyword(s):  
Control Plant ◽  
Pythium Ultimum ◽  
Plant Diseases ◽  
Disease Suppression ◽  
Compost Tea ◽  
Damping Off ◽  
Bacterial Populations ◽  
Production Methods ◽  
Tea Production ◽  
Relationship Of

Compost tea is being used increasingly in agricultural production to control plant diseases. However, there has been limited investigation relating disease control efficacy to various compost tea production methods, particularly compost tea produced with active aeration and additives to increase microbial population densities in compost tea. Aerated compost tea (ACT) and nonaerated compost tea (NCT), produced with or without additives, was investigated for the suppression of damping-off of cucumber caused by Pythium ultimum. Compost tea was used to drench soilless container medium inoculated with P. ultimum; effect on damping-off ranged from not suppressive to consistently suppressive depending on the method used to produce the tea. The most consistent formulation for damping-off suppression was ACT produced with kelp and humic acid additives. Producing ACT with a molasses-based additive inconsistently suppressed damping-off; evidence suggests that residual nutrients can interfere with disease suppression. Heating or diluting compost tea negated suppression. Across all compost tea samples, there was no significant relationship of bacterial populations, measured as active cells, total cells, or CFU, to disease suppression. However, for all ACT produced without the molasses-based additive, there was a threshold of bacterial population density (6 log10 active cells per ml, 7.48 log10 total cells per ml, or 7 log10 CFU per ml) above which compost teas were suppressive.

scholarly journals Seed-Colonizing Microbes from Municipal Biosolids Compost Suppress Pythium ultimum Damping-Off on Different Plant Species

2008 ◽  
Vol 98 (9) ◽  
pp. 1012-1018 ◽  
Author(s):  
M.-H. Chen ◽  
E. B. Nelson
Keyword(s):  
Plant Species ◽  
Pythium Ultimum ◽  
Disease Suppression ◽  
Microbial Consortia ◽  
Damping Off ◽  
Microbial Species ◽  
Pathogen Suppression ◽  
Municipal Biosolids ◽  
Leaf Compost ◽  
Biosolids Compost

Composts are known for their suppressive properties toward many different seed- and root-infecting pathogens and diseases. Although disease and pathogen suppression induced by composts is believed to be mediated by microbial activities, the nature of the microbial species and processes responsible for suppressiveness remain unknown. We demonstrated previously that seed-colonizing microbial consortia from leaf compost could explain the observed levels of Pythium ultimum-induced damping-off suppression on cotton. The aim of the present work was to determine whether seed-colonizing microbial consortia could explain Pythium damping-off suppression in municipal biosolids compost on three different plant species. Significant levels of disease suppression were observed on cucumber, wheat, and pea at water potentials of –2 kPa. The suppression of damping-off on cucumber and wheat could be eliminated by autoclaving the compost prior to sowing. High levels of suppressiveness were expressed both on cucumber and on wheat seed surfaces within 8 h of sowing. However, the expression of damping-off suppression on the surface of pea seeds was inconsistent and highly variable. Our results demonstrate that compost-induced suppression of P. ultimum damping-off of cucumber and wheat can be explained by the microbial consortia colonizing seeds within 8 h of sowing. These results further suggest that disease suppression in composts is related to microbial species that interact with the pathogen in its infection court and not in the bulk compost.

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