Diversity of prokaryotes (Chapter 11)

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Diversity of prokaryotes (Chapter 11) In
morphology In habitat In metabolism Basics of
metabolism energy source (of electrons,
ultimately used for ATP synthesis) electrons
are eventually transferred to a terminal
electron acceptor (oxygen for us) many
prokaryotes can use different terminal electron
acceptors
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Organisms need energy AND carbon for metabolism
Carbon sources? Autotrophs make sugar from
CO2 So a photoautotroph uses light for energy and
CO2 as a carbon source Heterotrophs- something
other than CO2 such as sugar (organic) So a
chemoheterotroph uses organic molecules for
energy and for carbon
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Where does the energy (i.e., electrons) come
from? Some organisms use sunlight
(phototrophs) (serve as food sources for
everything else) Other organisms use organic
sources (like sugar!) chemotrophs Some use
inorganic molecules (lithotrophs) Prokaryotes
can be classified further based on carbon source
and energy source
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Aerobes- terminal electron acceptor is
oxygen most efficient at generating
ATP Anaerobes- inorganic molecule is
terminal electron acceptor (e.g., S, SO4-,
NO3- or NO2-) less efficient than aerobic
respiration Fermenters- use organic molecule as
terminal electron acceptor (such as
pyruvate) least efficient See pp. 269-271 for
examples
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Significance of prokaryotic diversity Live in
many environments where eukaryotes cant Help
convert substances like nitrogen and sulfur to
forms other organisms can use
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Anaerobic lithotrophs may have been among
the earliest on Earth no oxygen few living
organisms (no source of organic material)
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Where do anaerobic environments exist
today? Soils aerobes consume existing oxygen
(so anaerobes can grow) Aquatic
environments Various internal environments
(even our mouths!) Obligate anaerobes are
killed by oxygen (Clostridium) facultative
anaerobes use oxygen but can grow without it (E.
coli) aerotolerant bacteria dont use oxygen
but are not killed by it (Streptococcus)
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Survey of representative microbes Terminology Ex
amples Significance in environment We start to
distinguish between eubacteria and archaea
(extreme environments)
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Anaerobic chemoorganotrophs Eubacteria-
high-sulfur-content mud often found in
communities with other bacteria help cycle
sulfur- what is its use in cells? how do we know
when sulfur is being metabolized? Fermenters
are important medically and in the food
industry Archaea hyperthermophiles
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Anaerobic chemolithotrophs (see p. 274) Oxidize
inorganic molecules like hydrogen gas (and
produce what?) Use carbon dioxide or sulfur as
electron acceptor Methanogens- produce methane
and water grow in sewage, intestinal tracts,
etc. Hard to culture, but may be a significant
alternative energy source Others reduce sulfur
in anaerobic soils
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Anaerobic chemoorganotrophic fermenters Do NOT
use Krebs cycle or electron transport in ATP
synthesis End products vary among
species Clostridium- ferment many compounds and
produce many different end products obligate
anaerobes Lactic acid bacteria- OBLIGATE
fermenters produce lactic acid even if oxygen
is present Streptococcus, Lactobacillus, etc.
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Significance of fermentation

• Some products are useful commercially (slide 15)
• Useful for identifying bacteria (e.g., coliforms
  are lactose fermenters)
• Distinguish obligate from facultative

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Lactobacillus, Lactococcus important
in commercial fermentation processes Yeast-
bread, beer, wine Lactose fermenters- cheese,
yogurt Propionibacterium- also used in
cheese production makes CO2 (like yeast)
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anoxygenic phototrophs Usually found in
aquatic habitats shallow enough to obtain light
for energy do NOT use water as electron source
therefore do not produce oxygen Bacteriochlorop
hyll absorbs wavelengths of light that
penetrate water Purple sulfur bacteria usually
require H2S Purple nonsulfur bacteria do not
more diverse metabolically (and in
habitat) Pigments contained within cell membrane
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Mechanisms of photosynthesis, p. 157
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Green bacteria pigments contained within
chlorosomes sulfur and non-sulfur forms Can
also grow in the dark Other such organisms have
been found, but are harder to observe Winogradsk
y columns are useful for culture
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Winogradsky column- prokaryote diversity
and interdependence
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Oxygenic phototrophs cyanobacteria Essential as
primary producers Morphologically diverse-
shapes, mobility, presence of sheaths,
etc. Contain chlorophyll and psychobiliproteins
to harvest energy from light Nitrogen-fixing
cyanobacteria fix N2 as well as CO2 from the
atmosphere Enzyme is contained within a
protective heterocyst (protects it from oxygen)
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Different types of cyanobacteria
Can float form mats
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Heterocyst protects enzyme from oxygen
Helps provide nutrients for other organisms
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Overgrowth of cyanobacteria can produce nuisance
blooms
Algae can do this, too
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Why does this happen, and why does it matter?

• Nutrients are usually limiting
• Organic waste (runoff) provides nutrients
• Photosynthetic organisms grow rapidly
• Decomposers eat them use up all the oxygen
• What happens to the larger life forms if the
  oxygen is used up?

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Aerobic chemolithotrophs Oxidize sulfur,
nitrogen, hydrogen Sulfur oxidizers generate
H2SO4 may be filamentous or unicellular contribu
te to acid runoff (Thiobacillus) some can
oxidize other metals Nitrifiers- help cycle
nitrogen in soil oxidize ammonium, nitrite
(nitrate is less toxic, can be taken up by
plants)
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A few representative pathways

• Recall Winogradsky column these organisms depend
  on each other
• Essential for nutrient cycling

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Aerobic chemoorganotrophs some are ubiquitous,
some are specialized May be obligate aerobes or
facultative anaerobes Obligate aerobes cannot
ferment molecules for energy Micrococcus,
Mycobacterium, Pseudomonas Thermus-
extremophile Deinococcus- radiation- resistant
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Facultative anaerobes Corynebacterium
(genus) Enterobacteriaceae (family)
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How do bacteria survive in so many
different environments? Resistance
stages endospores (Clostridium, Bacillus) soil
bacteria cysts (Azotobacter) nitrogen
fixers fruiting bodies (Myxobacteria) decompose
rs filaments (Streptomyces) produce antibiotics
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Bacteria and their animal hosts On skin-
Staphylococcus On mucous membranes respiratory-
Streptococcus, Lactobacillus many reside in GI
tract (How do they get there?) Many organisms of
diverse morphology and microenvironment
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Obligate intracellular parasites Lack full
biosynthetic capacity Rickettsia (vector-borne
ticks, lice) Coxiella (shed by one animal,
inhaled by another). May also be
vector-borne Chlamydia (person-to-person
contact) unusual physical and growth features
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Archaea- extreme bacteria Euryarchaeota-
methanogens extreme halophiles (salt-loving
bacteria) membranes contain bacteriorhodopsin (e
nables them to obtain energy from sunlight) Cren
archaeota- both groups contain extreme thermophil
es some generate methane some reduce
sulfur some are thermophilic acidophiles
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Summary bacteria can be found just about
anywhere on Earth! we sue this information to
help identify microorganisms Questions
about evolution (when did they appear what can
they tell us about conditions on
ancient Earth?) their role in maintaining
ecological balance metabolic products of
interest colonization of living organisms
pathogenesis treatment