Erwinia amylovora

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A Microbial Biorealm page on the genus Erwinia amylovora


Classification

Higher order taxa

Bacteria; Proteobacteria; Gammaproteobacteria; Enterobacteriales; Enterobacteriaceae; Erwinia


Genus species

Erwinia amylovora


Description and significance

Erwinia amylovora is a gram negative, motile, facultative anaerobic, rod shaped bacteria. It is negative for the Voges-Proskauer test and positive for gelatin hydrolysis and it releases gas when it undergoes glucose fermentation (1). Fire blight, a disease that affects and can cause extensive damage to apple and pear trees, is caused Erwinia amylovora. It received its name from the appearance of the infected plane, which often appears blackened as if it was scorched by fire (4). It can destroy apple and pear blossoms, shoots, limbs, and even whole trees (2). It can also affect other plants in sub-family Pomoideae of the family Rosaceae3. It is native to North America but spread to northern Europe in the 1950s and 1960s. It has continued to spread throughout the eastern Mediterranean since the 1980s and throughout Europe (3). The bacteria can enter the plant through its blossoms, stomata, or wounds on various parts of the plant and is often carried by rain or insects (3). Some of the common symptoms include the blossom blight, shoot blight, canker blight, trauma blight, and rootstock blight (2). In some cases the bacteria can be seen as a white or golden ooze seeing from the infected plant tissue (3). Once it infects the tree it spreads rapidly and there is often no way to save the infected tree (3).



Genome structure

Cell structure and metabolism

Ecology

Pathology

Erwinia amylovora is a casual pathogen that causes the contagious disease fireblight. Fireblight mainly affects pears, apples, and ornamental plants of the Roseaceae family. Infections typically begin in spring due to optimal moisture and temperature conditions. The first sign of infection is a blossom with a water-soaked appearance. If the infection is not controlled and the infection progresses the blossoms, shoots and branches will wilt, ooze, and die. Erwinia amylovora can survive over winter in cankers and become an active infection again in spring.

The affected areas of the plants appear shriveled and blackened as if they were scorched by fire; hence the term “fireblight.” A primary infection occurs when the bacterium enters the plant via open stomata. Consequently, necrotic lesions and bacteria-laden exudate engulf the plant. The death of the plant often occurs once the roots have been invaded. Streptomycin antibiotic sprays have been shown to prevent the spread of infection. Other techniques, such as pruning—the removal of infected areas—have also proved to be an adequate measure to save the plant.

Erwinia amylovora is found mostly in the Northern Hemisphere in places like North America, Canada, Europe, but also in New Zealand. Erwinia amylovora can cause severe outbreaks leading to loss of flower and subsequently, loss of fruit. This bacterium more harshly affects young trees.

The two main agents used as antimicrobial agents against Erwinia amylovora are copper and streptomycin. However, strains of Erwinia amylovora resistant to streptomycin have been reported in various geographic areas. Methods of prevention include but are not limited to controlling how lush the trees are especially during youth, sterilizing pruning equipment, and removal of formed cankers.


References

1. J. G. Holt et. al. Bergey’s Manual of Determinative Bacteriology.

2. Wilcox, Wayne. “Fire Blight” http://www.nysaes.cornell.edu/pp/extension/tfabp/firepm.shtml

3. EPPO. “Data Sheets on Quarantine Pests: Erwinia amylovora” http://www.eppo.org/QUARANTINE/bacteria/Erwinia_amylovora/ERWIAM_ds.pdf

4. “Fire Blight” http://en.wikipedia.org/wiki/Erwinia_amylovora

5. Percy, H. "HortFACT - Fire blight (Erwinia amylovora) in apples and pears - An Introduction to the Disease." 22 Apr. 2009 <http://www.hortnet.co.nz/publications/hortfacts/hf205017.htm>.

Created by students of M Glogowski, Jonathan Everson, Erin Koller, Adam Kennedy, Amanda Bowler, and Jennifer Cox