1esc 590.bacteria
TRANSCRIPT
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Soil Biota
Reading Assignment
Soil Microbiology:An exploratory
ApproachChapter 4, 5,6 & 7
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Bacteria: Features
1.One-celled organisms, whose genetic material
are not enclosed in a special nuclear material.
About 4-5 mm (0.004-0.005mm)
2. Lack nuclear membrane and thus are termed
prokaryotic.
3. Nucleoplasms not separated from cytoplasm.
4. Cell walls composed principally ofpeptidoglycans.
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5. Reproduction of binary fission.
6. Genetic exchange accomplished by conjugation and
transduction.
7. Appendages called flagella. Many swim by means ofwhiplike
Conjugation involves large transfer of genetic materialsbetween donor and recipient cells in mating.
Transduction involves direct genetic exchange of DNA byvirus attacking bacteria (bacteriophage).
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Groupings
1 Energy Source
a.Light as energy source -phototrophic
b. Chemicalas energy source-chemotrohic
2. Carbon Sources.
a. CO2 as C source- Lithotrophic (autothrophic) b. Organic substrate as C source- Organotrophic
(hterrotropjic)
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Groupings
Photolitotrophs - Higher plants, algae,
cyanobacteria, green sulfur bacteria.
(Photoautotroph).
Chemoorganotrophs - Require preformed organic
nutrients as their energy and carbon sources
(Heterotrophs).
Chemolithotrophs -Energy sources include NH4+,NO2-, Fe2+, S2-, S2O32-(Chemoautotrophs).
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Groupings
Photolitotrophs - Higher plants, algae,
cyanobacteria, green sulfur bacteria.
(Photoautotroph).
Chemoorganotrophs - Require preformed organic
nutrients as their energy and carbon sources
(Heterotrophs).
Chemolithotrophs -Energy sources include NH4+,NO2-, Fe2+, S2-, S2O32-(Chemoautotrophs).
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Groupings
3. Ecological Groupings
i. Autochthonous (indegenous)- grow slowly in
soils containing no easily oxidizable substrates.Humus degraders.
Indeginous populations may have resistant stages
and endure long periods without being active
metabolically, but at some time these nativesproliferate and participate in the biochemical
functions of the community.
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Groupings
ii. Zymogenous grow very fast on fresh residues
in soil. Opportunists.
a. K-Selected Species - Adapted to livng underconditions of bountiful supply of energy.
b. R-Selected Species -Live in uncrowded but
physically restrictive environments.
iii. Invaders or Allochthonous- These do notparticipate in community.
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Groupings
activities. They enter with precipitation, disesed
tissues, animal manure , or sewage sludge, and
they may persist for some time in a resting form.
They never contribute significantly to the various
ecological transformations and interaction.
Not widely used now
New terms are now Oligotrophy and Copiothropyrespectively
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Groupings
4. Morphological
a. Cocci- Usually round, but may also be oval,elongated or flattened on one side.
b. Bacillus
c. Spirillum- Have distinctive helical shape like acorkscrew, their cell bodies are fairlyrigid.
d. Pleomorpism -Have may shapes, not just one ina life- time
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Groupings
5. Aeration Status
a. Aerobes -O2 required
b. Anaerobes -O2 not required
c. Facultative -Grows in the
presence or absence of O2.
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Groupings
6. Cell Wall Chracteristics
Gram-Positive:
Plasma membrane is surrounded but thick cellwall
Cells have peptidoglycan and teichoic acids
Gram negative:
Have thinner cell wall which is surrounded byouter cell membrane.
Has peptidoglycan but lack teichoic acids.
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Conventional Taxonomy and GC ratios
Guanine + Cytosine content of DNA
G +C/A+T + G + C x 100%
GC ratio vary over wide range from 20 to
80 %
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Generating Phylogenetic Trees from
RNA sequences
1. Pure Culture
2. Amplify genes encoding 16S ribosomalRNA from genomic DNA using PCR
3. Sequence PCR product
4. Analyze data by computer analysis
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Steps In Biodiversity Analysis of
Microbial Community
1. Extract DNA
2. Ribosomal DNA obtained by PCR
3. Run Gel
4. Sequence and compare clones
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Importance of Soil Bacteria
1. Higher amount in soil than counted in
plate.
2. Most important group in soil.
3. Contain members that grow rapidly.
4. Cannot readily degrade lignin.
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5. Important in reduction of inorganic
compounds.
6. Most important in the degradation ofsynthetic biodegradable compounds
7. Most soil bacteria are heterotrophs. Few
are autotrophs.
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Importance of Soil Bacteria
Common Soil Bacteria.
1. Arthrobacter -lot of unusual shapes; K strategist.
2. Bacillus -spore formers; R-strategists
3. Pseudomonas -tend to degrade a lot of things; R-strategists
4. Agrobacterium
5. Alcaligens
6. Corynebacterium -K-strategist, non-sporeforming
7. Micrococcus -Highly underestimated
8. Staphylococcus
9. Xanthomonas
10. Mycobacter ium Acid fast, less common and small significance
11. Sarcina
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Common Bacteria in Soils
1. Pseudomonas
G- , straight or curves rods with polar
flagellata. Aerobic except denitrifying groups
Organotrophic (most), few lithotrophic
Some are pathogenic
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Attack a wide range of organic substrates
including sugars, amino acids, alcohols, and
synthetic pesticides. Many species produce pigments in media
especially iron media.
Yield 3-15 % of colonies on agar Involved in may soil transformations
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Common Bacteria in Soils
2. Arthrobacter
Members of this genus are the numerically
predominant bacteria in the soil asdetermined by plate counts
Account for 5-60% of plate counts
Numerically predominate in soil ( asdetermined by plate count) 40% of the totalplate count .
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Characterized by pleomorphism and Gram
variability
Slender, gram negative (G-) rod in early stage of
growth.
Very short gram positive (G+) rods and coccoid at
later stage of growth
Slow growers and poor competitors in the earlystages of residue decomposition; K-strategist.
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Common Bacteria in Soils
3. Bacillus:
7-67% , About 5-20 of the total bacterial
count as determined by plate counting.Numbers quite high, about 106 to 107 or
more/gram soil
Gram negative (G-) to Gram positive (G+)variable rods
Most species are motile
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Common Bacteria in Soils
Heat resistant endospores are placed andsporulation is not repressed by exposure toair.
Most are vigorous organothrophs
Metabolism is strictly respiratory, strictlyfermentative or both.
Some species are facultative litotrophs thatuse H2 as energy source in
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Common Bacteria in Soils
the absence of carbon.
B. polyxyxa fixes N2
B. thuringiensis is pathogenic to someinsect larvae and is widely used as a
biological control agent.
B.anthacis highly virulent animal pathogen-causes anthrax
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Common Bacteria in Soils
B macerans used for netting flax
Temp tolerance ranges from 5-70oC
Tolerance to acid ranges from pH 2-8 Salt tolerance is as high as 25% NaCl
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Common Bacteria in Soils
4. Clostridium
Sporogenic species
Most species are strict anaerobes Few are microaerophilic
Plate counts show 103 to 107 cells/g soil
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Genus of economic importance; its speciesare used commercially for the production ofalcohols and commercial solvents.
Several species, C. butyricum and C.pasteurianum are known to fix N2.
Genus is widely distributed in soils, marine,
and freshwater sediments; manures, andanimal intestinal tract.
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Pathogenic forms in this genus include
C..tetaniand C. botul inum.
Part 15 Bergey's manual
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Common Bacteria in Soils
5. Xanthomonas
Uses O2 as the only electron acceptor
Nitrates are not reduced Xanthomonas species are pathogenic to
plants.
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Common Bacteria in Soils
6. Other Soil Bacteria
a. Azotobacter -aerobic organotrophic
capable of fixing N2 symbiotically.b. Agrobacterium- Induces galls or other
hypertrophies, such as hairy roots, on
plants but does not fix N2.
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Common Bacteria in Soils
c. Nitrobacter and Nitrosomonas arechemolititrophic general which causenitrification in soil.
NH4+ NO2-
NO2 NO3-
d. Thiobacillus: sulfur compounds to
SO42-
S + 11/2O2 + H2O H2SO4