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CHAPTER 27

THE BACTERIA

AND ARCHAEA

Prepared by

Brenda Leady, University of Toledo

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One of the most prominent features of the bacteria and archaea is their diversity

Only 1% of newly discovered species have been cultured in the lab

Most species are known only as distinctive molecular sequences

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ProkaryotesLack nuclei and other cellular features typical

of eukaryotes Domain Archaea Domain Bacteria (or Eubacteria)

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Domain Archaea

Possess a number of features in common with the eukaryotic nucleus and cytoplasm, suggesting common ancestryHistones

Membrane linkages different from those in eukaryotes or bacteriaMore resistant to heat and other extreme

conditions

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Extremophiles

Can occupy habitats with very high salt content, acidity or methane levels, or high temperatures

Methanopyrus grows in deep-sea thermal vents at 98°C

Sulfolobus grows in hot springs at pH3 Halophiles

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Domain Archaea

Kingdom CrenarchaeotaSulfolobus and others that grow in extreme hot or

cold Kingdom Euryachaeota

Methane producers and extreme halophiles Kingdom Korarchaeota

Hot springs Kingdom Nanoarchaeota

Hyperthermophiles

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Domain Bacteria

50 or so bacterial phyla Structural and metabolic features of half

unknown Many more bacteria favor moderate

conditions

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Proteobacteria Amazing diversity of form and metabolism 5 major subgroups

α-proteobacteria Ancestors of mitochondria, Rhizobium, Agrobacterium

β-proteobacteria Nitrosomonas, Neisseria

γ-proteobacteria Vibrio, Salmonella, Escherichia coli

δ -proteobacteria Myxobacteria, bdellovibrios

ε –proteobacteria Helicobacter

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Cyanobacteria

Photosynthetic bacteria abundant in fresh waters, oceans and wetlands and on surfaces of arid soils

Named for blue-green or cyan color The only prokaryotes that generate oxygen as

a product of photosynthesis Gave rise to plastids of eukaryotic algae and

plants

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Display the greatest structural diversity found among bacterial phylaSingle cells or coloniesFilaments

Essential ecological roles in producing organic carbon and fixing nitrogen

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Horizontal gene transfer

Also known as lateral gene transfer Movement of one or more genes from one

species to another Contrasts with vertical gene transfer from

parent to progeny Horizontal gene transfer increases genetic

diversity Influences the methods used to infer the

phylogeny of bacteria and archaea

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Can result in large genetic changes At least 17% of the genes present in the

common human gut inhabitant E. coli came from other bacteria

Allowing new metabolic processes to be acquired despite lacking the sexual processes typical of eukaryotes.

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Potential to interfere with human efforts to deduce evolutionary relationships

Molecular systematists employ ribosomal RNA (rRNA) genes and other sequences thought to less often move horizontally and thus more accurately reflect patterns of vertical inheritance

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Important concepts

Bacteria and Archaea evolved from a common ancestor

Eukaryotic nucleus and cytoplasm likely arose in an ancient archaeal organism

Mitochondria and plastids originated from proteobacteria and cyanobacteria by endosymbiosis

Bacteria and archaea are amazingly diverse, but many phyla and species lack scientific names because microbiologists know so little about them

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Structure and motility

Bacteria and archaea share small size, rapid growth, and simple cellular structure

Bacteria and archaea are 1–5 μm in diameter(most plant and animal cells are between 10 and

100 μm in diameter) Small cell size limits the amount of materials

that can be stored within cells but allows faster cell division

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Cellular structure

Prokaryotic cells are much simpler than eukaryotic cells

Thylakoids – ingrowths of plasma membrane that increase surface area for photosynthesis

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Magnetosomes – magnetite crystalsCompass likeHelps to locate low-

oxygen habitats

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Other examples of cell structure complexityNucleus-like bodies from plasma membrane

invaginationsCellular proteins similar to eukaryotic tubulin

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Cell shape and arrangement 5 major shapes

Spheres – cocciRods – bacilliComma-shaped – vibriosSpiral-shaped – spirochaetes are flexible while

spirilli are rigid Some occur as single cells, pairs, filaments Important diagnostic features

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Mucilage

Composed of polysaccharides, protein, or both

Secreted from cells Functions

Evade host defensesHold colony together – biofilms

Dental plaque

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Cell-wall structure

Maintain cell shape and help protect against attack

Also help avoid lysis in hypotonic solutions Archaea and some bacteria use protein Most bacteria use peptidoglycan

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Gram stain

Gram positive Relatively thick peptidoglycan layer Purple dye held in thick layer Cells are stained purple Vulnerable to penicillin that interferes in cell wall synthesis

Gram negative Less peptidoglycan and a thin outer envelope of

lipopolysaccharides Lose purple stain but retain final pink stain Cell are stained pink Resists penicillin and requires other antibiotics

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Motility

Move to favorable conditions Respond to chemical signals Swim, twitch, glide or adjust floatation

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Flagella

Swimming Different from

eukaryotic flagella Like an outboard boat

motor Differ in number and

location of flagella

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Pili

Twitch or glide Threadlike cell

surface structures

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Gas vesicles

Cyanobacteria Adjust buoyancy Move up or down in water column

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Binary Fission

Divide by splitting in two Basis for widely used method of detecting

and counting bacteria in samplesPlace measured volume of sample into plastic

dishes of agarSingle cells will form visible colonies

Can also use fluorescent dye that binds bacterial DNA to directly count bacteria

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Surviving harsh conditions

AkinetesDevelop when stressedCan germinate into metabolically active cells

under favorable conditionsAquatic filamentous cyanobacteria

EndosporesTough protein coatAmazingly long dormant spanBacillus anthracis, Clostridium botulinum,

Clostridium tetani

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Obtaining genetic material

TransductionVia viral vector

TransformationVia uptake of DNA from environment

ConjugationVia mating with another cell

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Nutrition and metabolism

More diverse types of metabolism than any other group of organisms

Can be classified byNutritionResponse to oxygenPresence of specialized metabolic processes

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Nutrition classification

Autotrophs Produce all or most of their own organic compounds

Photoautotroph – uses light as energy source for synthesis of organic compounds from CO2 or H2S

Chemoautotrophs – use energy obtained from chemical modification of inorganic compounds to synthesize organic compounds

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Heterotrophs - organisms that require at least one organic compound, and often more

Photoheterotroph – able to use light energy to make ATP but they must take in organic compounds from the environment

Chemoorganotroph – must obtain organic molecules for both energy and carbon source

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Classification by oxygen response

Obligate aerobes – require oxygen Facultative aerobes – can use oxygen or

not Obligate anaerobes – cannot tolerate

oxygen Aerotolerant anaerobes – do not use

oxygen but are not poisoned by it

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Classification by special metabolism

Diazotrophs – conduct nitrogen fixationEnzyme nitrogenase converts inorganic

nitrogen gas into ammoniaPlants depend on ammonia to make nitrogen

containing compoundsRhizobiumHeterocysts – specialized cells

Gene Expression Studies Revealed How Cyanobacteria Fix Nitrogen in Hot Springs

Thermal pools display multicolored microbial mats Composed of diverse nutrition types In Yellowstone, Synechococcus are the only

photoautotrophs High temperatures allowed few nitrogen fixers Synechococcus was producing its own fixed

nitrogen Tracked process using gene expression

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Ecological roles

Carbon cycleProducers synthesize organic compounds

used by other organisms as foodDecomposers (saprobes) break down dead

organisms to release minerals for reuseMethanogens make methaneMethanotrophs consume methane

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Symbiotic roles

MutualismAssociation beneficial to both partnersMany aquatic protists depend on bacterial

partners for vitamins Parasitism

One partner benefits at the expense of the otherPathogens – cholera, leprosy, tetanus,

pneumonia, Lyme Disease, etc.

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Industrial and other roles

Dairy products (cheese and yogurt) Vinegar, amino acids, enzymes, vitamins,

insulin, vaccines, antibiotics, etc. Useful in treating wastewater, industrial effluent,

and other harmful substances Bioremediation

Agriculture – Bacillus thuringiensis produces Bt-toxins

The Daly Experiments Revealed How Deinococcus radiodurans Avoids Radiation Damage

Unusually resistant to chemical mutagens and nuclear radiation

Radiation-resistant bacteria tended to have higher levels of manganese

Exact mechanism of protection not yet established