1ESC 590.Bacteria

7/30/2019 1ESC 590.Bacteria

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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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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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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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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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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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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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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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5. Xanthomonas

Uses O2 as the only electron acceptor

Nitrates are not reduced Xanthomonas species are pathogenic to

plants.


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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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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

1ESC 590.Bacteria

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