Erwinia amylovora auxotrophic mutant exometabolomics and virulence on apples

Sara M. Klee, Judith Pawloski Sinn, Melissa Finley, Erik L. Allman, Philip B. Smith, Osaretin Aimufua, Viji Sitther, Brian L. Lehman, Teresa Krawczyk, Kari Anne Peter, Timothy W. McNellis

Research output: Contribution to journalArticle

Abstract

The Gram-negative bacterium Erwinia amylovora causes fire blight disease of apples and pears. While the virulence systems of E. amylovora have been studied extensively, relatively little is known about its parasitic behavior. The aim of this study was to identify primary metabolites that must be synthesized by this pathogen for full virulence. A series of auxotrophic E. amylovora mutants, representing 21 metabolic pathways, were isolated and characterized for metabolic defects and virulence in apple immature fruits and shoots. On detached apple fruitlets, mutants defective in arginine, guanine, hexosamine, isoleucine/valine, leucine, lysine, proline, purine, pyrimidine, sorbitol, threonine, tryptophan, and glucose metabolism had reduced virulence compared to the wild type, while mutants defective in asparagine, cysteine, glutamic acid, histidine, and serine biosynthesis were as virulent as the wild type. Auxotrophic mutant growth in apple fruitlet medium had a modest positive correlation with virulence in apple fruitlet tissues. Apple tree shoot inoculations with a representative subset of auxotrophs confirmed the apple fruitlet results. Compared to the wild type, auxotrophs defective in virulence caused an attenuated hypersensitive immune response in tobacco, with the exception of an arginine auxotroph. Metabolomic footprint analyses revealed that auxotrophic mutants which grew poorly in fruitlet medium nevertheless depleted environmental resources. Pretreatment of apple flowers with an arginine auxotroph inhibited the growth of the wild-type E. amylovora, while heat-killed auxotroph cells did not exhibit this effect, suggesting nutritional competition with the virulent strain on flowers. The results of our study suggest that certain nonpathogenic E. amylovora auxotrophs could have utility as fire blight biocontrol agents.

Original languageEnglish (US)
Article numbere00935-19
JournalApplied and environmental microbiology
Volume85
Issue number15
DOIs
StatePublished - Jan 1 2019

Fingerprint

Erwinia amylovora
auxotrophs
Malus
virulence
Virulence
apples
arginine
Arginine
flower
shoot
mutants
biocontrol agent
hexosamines
immune response
tobacco
flowers
Hexosamines
Pyrus
footprint
inoculation

All Science Journal Classification (ASJC) codes

  • Biotechnology
  • Food Science
  • Applied Microbiology and Biotechnology
  • Ecology

Cite this

Klee, Sara M. ; Sinn, Judith Pawloski ; Finley, Melissa ; Allman, Erik L. ; Smith, Philip B. ; Aimufua, Osaretin ; Sitther, Viji ; Lehman, Brian L. ; Krawczyk, Teresa ; Peter, Kari Anne ; McNellis, Timothy W. / Erwinia amylovora auxotrophic mutant exometabolomics and virulence on apples. In: Applied and environmental microbiology. 2019 ; Vol. 85, No. 15.
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abstract = "The Gram-negative bacterium Erwinia amylovora causes fire blight disease of apples and pears. While the virulence systems of E. amylovora have been studied extensively, relatively little is known about its parasitic behavior. The aim of this study was to identify primary metabolites that must be synthesized by this pathogen for full virulence. A series of auxotrophic E. amylovora mutants, representing 21 metabolic pathways, were isolated and characterized for metabolic defects and virulence in apple immature fruits and shoots. On detached apple fruitlets, mutants defective in arginine, guanine, hexosamine, isoleucine/valine, leucine, lysine, proline, purine, pyrimidine, sorbitol, threonine, tryptophan, and glucose metabolism had reduced virulence compared to the wild type, while mutants defective in asparagine, cysteine, glutamic acid, histidine, and serine biosynthesis were as virulent as the wild type. Auxotrophic mutant growth in apple fruitlet medium had a modest positive correlation with virulence in apple fruitlet tissues. Apple tree shoot inoculations with a representative subset of auxotrophs confirmed the apple fruitlet results. Compared to the wild type, auxotrophs defective in virulence caused an attenuated hypersensitive immune response in tobacco, with the exception of an arginine auxotroph. Metabolomic footprint analyses revealed that auxotrophic mutants which grew poorly in fruitlet medium nevertheless depleted environmental resources. Pretreatment of apple flowers with an arginine auxotroph inhibited the growth of the wild-type E. amylovora, while heat-killed auxotroph cells did not exhibit this effect, suggesting nutritional competition with the virulent strain on flowers. The results of our study suggest that certain nonpathogenic E. amylovora auxotrophs could have utility as fire blight biocontrol agents.",
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Erwinia amylovora auxotrophic mutant exometabolomics and virulence on apples. / Klee, Sara M.; Sinn, Judith Pawloski; Finley, Melissa; Allman, Erik L.; Smith, Philip B.; Aimufua, Osaretin; Sitther, Viji; Lehman, Brian L.; Krawczyk, Teresa; Peter, Kari Anne; McNellis, Timothy W.

In: Applied and environmental microbiology, Vol. 85, No. 15, e00935-19, 01.01.2019.

Research output: Contribution to journalArticle

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T1 - Erwinia amylovora auxotrophic mutant exometabolomics and virulence on apples

AU - Klee, Sara M.

AU - Sinn, Judith Pawloski

AU - Finley, Melissa

AU - Allman, Erik L.

AU - Smith, Philip B.

AU - Aimufua, Osaretin

AU - Sitther, Viji

AU - Lehman, Brian L.

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AU - Peter, Kari Anne

AU - McNellis, Timothy W.

PY - 2019/1/1

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AB - The Gram-negative bacterium Erwinia amylovora causes fire blight disease of apples and pears. While the virulence systems of E. amylovora have been studied extensively, relatively little is known about its parasitic behavior. The aim of this study was to identify primary metabolites that must be synthesized by this pathogen for full virulence. A series of auxotrophic E. amylovora mutants, representing 21 metabolic pathways, were isolated and characterized for metabolic defects and virulence in apple immature fruits and shoots. On detached apple fruitlets, mutants defective in arginine, guanine, hexosamine, isoleucine/valine, leucine, lysine, proline, purine, pyrimidine, sorbitol, threonine, tryptophan, and glucose metabolism had reduced virulence compared to the wild type, while mutants defective in asparagine, cysteine, glutamic acid, histidine, and serine biosynthesis were as virulent as the wild type. Auxotrophic mutant growth in apple fruitlet medium had a modest positive correlation with virulence in apple fruitlet tissues. Apple tree shoot inoculations with a representative subset of auxotrophs confirmed the apple fruitlet results. Compared to the wild type, auxotrophs defective in virulence caused an attenuated hypersensitive immune response in tobacco, with the exception of an arginine auxotroph. Metabolomic footprint analyses revealed that auxotrophic mutants which grew poorly in fruitlet medium nevertheless depleted environmental resources. Pretreatment of apple flowers with an arginine auxotroph inhibited the growth of the wild-type E. amylovora, while heat-killed auxotroph cells did not exhibit this effect, suggesting nutritional competition with the virulent strain on flowers. The results of our study suggest that certain nonpathogenic E. amylovora auxotrophs could have utility as fire blight biocontrol agents.

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