Download FUNGI AND RELATED ORGANISMS

March 24 2008
• Finish Bacteria
• Molicutes
Virulence Factors
Bacterial Colonization
1. adhere to host cells and resist physical removal
2. contact host cells
3. invade host cells
4. resist innate immune defenses such as phagocytosis
5. evade adaptive immune defenses
6. compete for iron and other nutrients
Fastidious Bacteria
The term fastidious refers to the difficulty of obtaining pure
cultures of bacterium, due to special medium requirements,
slow growth, etc. "Fastidious" = fussy, meticulous.
Characteristics:
1. Bacilli
2. No flagellae (non-motile)
3. Most are Gm -, except for Clavibacter (Gm +) - causal
agent for ratoon stunt disease (RSD) of sugarcane,
bermudagrass stunt.
4. Sensitivity to high temperatures - hot air and water
treatments can kill them. Ex: RSD in sugarcane. Good
control is hot water treatment of seed cane.
FASTIDIOUS BACTERIA
Two Basic Groups:
1. Phloem limited - Can't be grown in pure
culture. Ex: citrus greening
FASTIDIOUS BACTERIA
Two Basic Groups:
1.
Phloem limited - Can't be grown in pure culture. Ex:
citrus greening
2. Xylem limited - can be grown in pure culture.
Ex: 1) Pierce's disease of grape - Xylella fastidiosa
2) Ratoon Stunting Disease (RSD) of sugarcane
(Leifsonia xyli (formerly Clavibacter xyli subsp.
xyli))
Symptoms of RSD
General decline of
ratooning (stubble crop)
Reddening of tissue
Sugarcane and RSD
In August 2006, 10% of crop is harvested for planting
Nitrogen application in Spring ‘07
Harvest in the Fall 2007
Sugarcane and RSD
Phytoplasmas and Spiroplasms
Kingdom Prokaryotae
cell membrane cell wall
Bacteria
+
Mollicutes (Phytoplasmas, Spiroplasmas)
+(3-layered)
+
-
Phytoplasmas
Initially found to cause a group of diseases called
"yellows" diseases.
These diseases initially were thought to be caused by
viruses because no fungi or bacteria were detected.
Essentially they are small, wall-less bacteria.
Characteristics of Phytoplasmas
1. No cell wall, so they tend to be pleomorphic. They
resemble mycoplasmas, which are known animal
pathogens. The name "mycoplasma" means "fungus form".
2. Specialized three-layered cell membrane instead of a
wall.
3. Extremely small - can be as small as 125 nm in diameter.
4. Can not be grown in pure culture
(i.e., no completion of Koch's postulates).
5. Fragile, very sensitive to osmotic changes.
Characteristics of Phytoplasmas
6. Gram 7. Inhibited by antibiotics (i.e., tetracycline) that do not
act by disrupting cell wall production (i.e., penicillin).
8. Transmitted by insects - leafhoppers (most important),
plant hoppers. Piercing-sucking mouthparts!
Phytoplasmas actually multiply within the salivary glands
of insect vectors.
Phytoplasmas are known to cause = 200 plant diseases.
Ex: aster yellows, bunchy top of papaya, pear decline,
lethal yellowing of palm.
• Website - Phytoplasma Casts A Magic
Spell
• www.apsnet.org/online/feature/poinsettia/top.html
The interactions between a phytoplasma and poinsettia result in
dwarfing and moderate branching growth habit, which happens to
be a trait that poinsettia growers desire.
Technically, free-branching is a disease symptom in poinsettias. But,
like the virus associated with classical color-breaking of tulip petals,
the poinsettia phytoplasma is beneficial to growers, generating
multi-flowered Christmas showpieces and $325 million annually.
Restricted-branching morphotype Free-branching induced by phytoplasma
Restricted-branching morphotype on left
Spiroplasmas
Similar in many regards to
phytoplasmas, except that they can be
cultured.
Characteristics of Spiroplasmas :
1. Small, helical organisms. They
resemble a corkscrew.
2. The are motile. Can somehow use
their corkscrew shape to propel
themselves.
Spiroplasmas
Similar in many regards to phytoplasmas, except that
they can be cultured.
Characteristics of spiroplasmas:
1. Small, helical organisms. They resemble a corkscrew.
2. The are motile. Can somehow use their corkscrew shape to
propel themselves.
3. No cell wall.
4. Specialized three-layered membrane.
5. Exhibit sensitivity to antibiotics that is similar to that
for phytoplasmas.
Common spiroplasma-induced diseases: Ex: brittle root
of horseradish, corn stunt
Corn Stunt
Symptoms are typical of phloem dysfunction:
Red leaves, green fruit, leaf dieback, bushy plants,
stunting.
Disease Cycle
The spiroplasma overwinters within the adult
leafhopper; when the leafhoppers emerge from
overwintering in early spring, they can be
infective.
Disease symptoms appear about 3 weeks
after the corn is infected.
Corn Stunt
Brittle Root