Plant Pathology - Bacteria

When was the first evidence of a bacterium causing fire blight discovered?

1878

When was pathogenic bacteria confirmed as the causal agent of fire blight, thus founding plant bacteriology?

1890

Prokaryotic

• Single-celled  

  • Organs within cell are not membrane-bound (loose)

What is a sign of bacterial infection?

Bacterial ooze - large aggregates of bacteria

Do all bacteria have cell walls?

No -

What shape do most plant pathogenic bacteria cells take?

Rod-shaped, some are round (coccal)

Bacteria that lack cell walls are…

Pleomorphic - no fixed shape, amorphous

Mollicutes

No cell walls restricting the shape

Bacterial cells have what types of DNA?

Chromosomal DNA - holds most of the genetic information for bacteria.
Non-chromosomal DNA - PLASMIDS - rings of DNA

What is a plasmid?

Non-chromosomal DNA that is physically separate from chromosomal DNA and can replicate independently.

Does plasmid DNA increase the virulence of pathogenic bacteria?

Yes - increases pathogenicity through quick replication, mutation, and adaptation. Increases antibiotic resistance.

What are pili?

bacterial appendages that promote adherence to surfaces, and can increase virulence factor of a pathogen. Not to be confused with flagellum.

What is the primary reproductive strategy for bacteria?

Binary fission - singe cell divides into two identical daughter cells after DNA replication

Is binary fission sexual or asexual reproduction?

Asexual - the daughter cells are genetic copies of the parent.

Where does bacterial genetic diversity come from?

Horizontal Gene Transfer

Conjugation

Horizontal transfer through the creation of a pilus (a bridge connection), moving the plasmid to recipient cell

How does conjugation increase genetic diversity?

During horizontal transfer, the pilus can break prematurely and cause incomplete transfer of plasmid, thus creating two cells with different DNA.

Transduction

Transfer of bacterial DNA from one cell to another via a bacteriophage (a virus that infects bacteria)

Bacteriophage

A virus that infects bacteria. Used in transduction and when phages are abundant.

Transformation

Taking up free DNA in the environment from compatible bacteria (homologous to its genome) - RARE

What is a symptom of plant pathogenic bacteria?

Wilt

What are signs of plant pathogenic bacteria?

Ooze, and bacterial mass

Obligate parasites

Need a living host

Epiphytes

Live on plant surfaces until conditions are favorable for infection

Are the large majority of bacteria aerobic or anaerobic?

Aerobic - needing oxygen

How do bacteria move through the environment?

Dissemination - windblown particles, animal facilitation (birds, insects, humans)

Infested

A surface contamination - remaining on the outside

Infected

Internal contamination

How do bacteria find their host?

Passively - no independent movement

Pectin

A glue for plant cell walls that bacteria feed on using pectinase. The feeding of pectin literally dissolves the cell walls, nothing to hold them together

Bacterial Disease triangle

Host + Pathogen + Environment - BUT cannot infect host without a vector/entry.

What are some symptoms of a plant pathogenic bacteria?

Galls, witch’s broom, water-soaking, angular leaf spots (cannot cross leaf veins), soft rots, wilting

How do you culture and identify bacteria?

Gram stain:

• Gram positive and negative

  • Most pathogenic bacteria are Gram negative

Selective media, immunoassays, PCR, ELISA