Download FUNGI AND RELATED ORGANISMS

Bacteria
Bacteria are small: 0.6-3.5 microns in length, 0.5-1.0
microns in diameter
http://www.cellsalive.com/howbig.htm
There are about several thousand species of bacteria
currently identified.
Most are strictly saprophytic and are important in the
decomposition of organic matter.
Several cause diseases in humans or animals, but only
about 100 species are plant pathogens.
Bacteria
Morphology and Characteristics:
1. Simple, unicellular
2. Shapes:
- coccus - spherical
- bacillus - rod shaped *** Most plant pathogens.
- spirillum - coiled
- filamentous - resemble fungal hyphae.
Ex. Streptomyces (see Fig. 12-4, page 411)
Bacterial
Morphology
Bacteria associated with plants have several morphological shapes as can be
seen with conventional microscopes at 400x to 1000x magnification.
Morphology
coccus
bacillus
filamentous
spirillum
Morphology and Characteristics:
3. Motility - all bacteria that are motile have delicate
threadlike flagellae which are considerably
longer than the length of the bacterial cell.
Flagellae typically are associated with bacilli.
Attachment of flagellae:
a. monotrichous - one flagellum
b. lophotrichous - 2 or more flagellae at one end
c. amphitrichous -1 or more flagellae at both ends
d. peritrichous - flagellae all over bacterium
Attachment of flagellae:
Multiplication:
http://www.cellsalive.com/qtmovs/ecoli_mov.htm
Bacteria divide by binary fission
(splitting into two equal parts). After the
new DNA has replicated, the
chromosomes attach to the cell wall and
are pulled apart.
Bacteria can multiply very fast (e.g. 20
minutes). At this rate, one bacterial cell
can produce 300 billion new cells in 24
hours. Most plant pathogenic bacteria
thrive in warm, moist weather.
Morphology and Characteristics:
4. They are prokaryotes - lack an organized nucleus.
5. Their cell walls lack cellulose.
6. They are surrounded by a protective layer of polysaccharide.
Believed to condition the immediate environment around the
bacterial cell. Important for:
• Resistance to desiccation
• Resistance to attack (eg. by phagocyts in animals)
• Attachment to surfaces
• Pathogenicity
• Antigenic: Can elicit host defense mechanisms
Bacterial Cell Wall
Primary function is to give rigidity to the cell.
Responsible for the shape of the cell.
Responsible for the osmotic stability.
Cell Wall with
Cell Membrane
Identification of Bacteria:
Generally rather difficult. In addition to morphology (shape and
flagellae), is based on results from a large array of tests, such as:
1.Gram stain reaction - tests ability of cell wall to stain with crystal
violet. Gm + stains with crystal violet, Gm - does not and must be
counterstained with safranin (red color).
Most plant pathogenic bacteria are Gm -. Main exceptions are:
Clavibacter, Streptomyces, Bacillus, Clostridium, and a few others.
2. Ability to liquefy gelatin
3. Ability to utilize different carbon sources
4. Production of acid or gas in culture
5. etc, etc, etc
Identification of Bacteria:
Gram + bacteria which have a
thick peptidoglycan layer retain
more crystal violet and appear
purple.
Gram - bacteria that have an
outer membrane and Mollicutes
that lack a cell wall enabling the
CM to stain, appear pink.
Important Genera of Plant
Pathogenic Bacteria:
1.
2.
3.
4.
5.
Agrobacterium
Clavibacter
Erwinia
Streptomyces
Pseudomonas
1/2 of all plant pathogens
6. Xanthomonas
1/3 of all plant pathogens
** Images and lecture material were not entirely created by J. Bond. Some of
this material was created by others.**
Bacteria are more influenced by environmental
conditions than any other plant pathogen.
This is why we generally have fewer epidemics
caused by bacteria than by fungi.
Bacteria have no enzymatic or mechanical means of
entering plants.
They enter through wounds or natural openings
such as hydathodes, lenticels, stomates,
nectaries, etc.
Physiological/Environmental
Constraints
1) Bacteria lack resistance to environment and long-distance dispersal
mechanisms
•Most are susceptible to desiccation. Very few bacteria form endospores.
•Most bacteria are also susceptible to damage by visible and UV radiation.
•Most are unable to disperse long distances without vectors.
•Some are unable to survive outside the plant or their insect vectors.
Constraints cont.
2) Bacteria lack active mechanisms to penetrate plants.
•May enter through natural openings including stomates, hydathodes,
nectaries, and lenticels and natural junctions including at lateral roots,
root hairs, leaves, stems, and flowers.
• May enter the plant via wounds caused by wind, hail, abrasion by
surrounding branches, animal or insect feeding, cultural practices, plant
development (e.g. leaf scars), lesions or wounds caused by other
pathogens.
.
Constraints cont.
3. Once they get into the plant, they have entered a relatively
humid but very nutrient poor environment surrounded by
multiple polymers (e.g. cellulose, hemicellulose, pectin) that
inhibit further spread.
Once inside the plant bacteria must increase the availability of
nutrients.
1. By altering the membrane permeability of the plant cells.
2. Agrobacterium reprograms the plant cells to produce nutrients
for themselves.
2. By producing cell wall degrading enzymes and/or toxins. Lysis
of the plant cell releases