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. Bacilli2. 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 BACTERIATwo 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

fastidiosa2) Ratoon Stunting Disease (RSD) of sugarcane (Leifsonia xyli (formerly Clavibacter xyli subsp. xyli))

Symptoms of RSD

Reddening of tissue

General decline of ratooning (stubble crop)

Sugarcane and RSDIn 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.

Free-branching induced by phytoplasma Restricted-branching morphotype

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 CycleThe 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