Dickeya dadantii

Erwinia chrysanthemi
Scientific classification
Kingdom:	Bacteria
Phylum:	Proteobacteria
Class:	Gamma Proteobacteria
Order:	Enterobacteriales
Family:	Enterobacteriaceae
Genus:	Erwinia
Species:	E. chrysanthemi
Binomial name
Erwinia chrysanthemi Burkholder et al. 1953
Synonyms
Pectobacterium chrysanthemi Erwinia carotovora var. chrysanthemi Pectobacterium carotovorum var. chrysanthemi Dickeya chrysanthemi Pectobacterium parthenii Pectobacterium parthenii var. dianthicola Pectobacterium parthenii var. chrysanthemi

Erwinia chrysanthemi is a gram-negative bacillus that belongs to the family Enterobacteriaceae. It is a close relative of E. coli and other animal pathogens that include Salmonella, Shigella, Klebsiella, Proteus and Yersinia. Members of this family are facultative anaerobes, able to ferment sugars to lactic acid, have nitrate reductase, but lack oxidases. Even though many clinical pathogens are part of the Enterobacteriaceae family, most members of this family are plant pathogens.

In the natural plant environment, Erwinias cause plant maladies such as necrosis, blight and “soft rot,” a progressive tissue maceration . Erwinia chrysanthemi contains many pectinases that are able to macerate and break down the plant cell wall material. This exposed part of the plant releases nutrients that can facilitate bacterial growth. Commonly infected plants include potato tubers, bulbs of vegetables, and ornamental crops.

Biology

Virulence is evident in this pathogen and is based on several biological strategies. The first adaptation utilized by E. chrysanthemi is a type II secretion system capable of producing a pilus that acts as a piston to extrude proteins. Another adaptation to plant hosts is the production of well adapted siderphores capable of scavenging iron from the environment known as chrysobactin and acromobactin. Originally Pectinase secretion was believed to be the major factor in the virulence of E. chrysanthemi. The current ideas combine the pectinase activity and siderophore synthesis in a model that demonstrates the homeostatic balance of iron. (Douet et al. 2008) There are many strains of Erwinia chrysanthemi. Specific strains that were tested in the articles used to write this entry include: Celery: CCRC13147-48 Corn: CCRC13151 Green onion: CCRC12616 Phalaenopsis: EchPB1, EchPL3, EchLy8, EchP2-1, EchPh1- EchPh20 Potato: CCRC13149, CCRC13150 Other related Erwinia species causing disease in horticultural crops include: E. cypripedii, E. nigrifluens, E. quercina, E. rhapontici.

Diversity and Identification

E. chrysanthemi is the member within the genus that is able to produce the pigment indigoidine. Rapid identification of this species utilizes this water insoluble blue pigment appearing in the bacterial colonies as a chemotaxonomic trait (Yung-An Lee et al, 2006). The presence of a soft rot may be an indication of a bacterial disease, however many other organisms and plant disorders may appear as various soft rot or black lesions. Proper identification is important for treatment and control measures. Thus a differential medium is used to culture Erwinia species and isolate or identify E. chrysanthemi. Researchers at Fu Jen Catholic University in Taiwan developed a medium that differentiates E. chrysanthemi from other species. This NGM media contains nutrient agar (NA) and glycerol medium supplemented with MnCl₂ :4H₂O. To make this medium mix 23g of nutrient agar, 10ml glycerol (1% v/v), and 0.4g MnCl₂:4H₂O (2mM) to 1.0 liter of water. Note the pH of this media is 6.5 and it has a light brown base color (Yung-An Lee et al, 2006). The proper temperature for culturing E. chrysanthemi is 28 degrees Celsius. A positive result occurs when a bacterial streak produces a brownish blue color on the agar plate. Further isolation and extraction of the indigoidine pigment is possible using the methods described by Chatterejee and Brown (1981).

Role in plant disease

Erwinia chrysanthemi also known as Dickeya causes soft rot disease in many horticulturally important ornamental plant crops and food crops. Soft rot may also be known as brown rot or blackleg to describe the appearance of the post infected tissues within the stems and leaves of mature plants. Erwinia chrysanthemi is a pathogen that infects the leaves and storage organs of herbaceous plants. In subterranean bulbs and tubers the disease appears as sunken and cracked externally and brown in cross section (M. Slawiak et al. 2009). Erwinia disease has been studied in commercially valuable Phalaenopsis orchids. Soft rot diseases caused by Erwinia spp'. Is one of the most devastating diseases in orchid production (Liau et al., 2003). Orchid growers have used environmental controls to provide the optimum growth conditions for the plants while minimizing the cultivation of the pathogens. Proper control of humidity and air movement combined with clean, high quality water, in a temperature and light regulated facility are the most commonly employed methods for disease prevention. Other biological controls of Erwinia disease include symbiotic fungi known as mycorrhiza and possibly transgenic proteins. Transfer of sweet pepper genes coding for ferredoxin like protein and defensin was shown to reduce Erwinia disease in Phalaenopsis orchids under cultivation (Liau et al.,2003: Chan et al.,2005). Under controlled conditions plants with mycorrhizal fungi such as Rizoctonia solani and Ceratobasidium sp demonstrated resistance to Erwinia disease (Po-Hung et al. 2011).

References

Chan YL, Lin KH, Sanjaya Liao LJ, Chen WH, Chan MT (2005). Gene Stacking in Phalaenopsis orchid enhances dual tolerance to pathogen attack. Transgenic Research. 14: 279-288

Chatterjee, A.K., Brown, M.A., (1981). Chromosomal location of a gene (idg) that specifies production of the blue pigment indigoidine in Erwinia chrysanthemi. Current Microbiology 6: 269-273

Douet, V., Expert, D., Barras, F., Py, B. (2008) Erwinia chrysanthemi Iron metabolism: the unexpected implication of the inner membrane platform within the type II secretion system. Journal of Bacteriology doi: 10.1128/JB.00845-08

Liau CH, Lu JC, Prasad V, Hsiao HH, You SJ, Lee JT, Yang NS, Huang HE, Feng TY, Chen WH, Chan MT (2003) The sweet pepper ferredoxin-like protein(pflp) conferred resistance against soft rot disease in Oncidium orchid. Transgenic Research. 12: 329-336.

Po-Hung Wu, Ding-Ding Huang and Doris C.N. Chang (2011) Mycorrhizal symbiosis enhances Phalaenopsis orchid’s growth and resistance to Erwinia chrysanthemi. African Journal of Biotechnology Vol.10(50), pp. 10095-10100.

Slawiak, M., Lojkowska, E., Van der Wolf, J.M. (2009) First report of bacterial soft rot on potato caused by Dickeya sp. (syn. Erwinia chrysanthemi) in Poland. Plant Pathology 58, 794

Yung-An Lee, Cheng-Pin Yu (2006) A differential medium for the isolation and rapid identification of a plant soft rot pathogen, Erwinia chrysanthemi. Journal of Microbiological Methods 64: 200-206.