Prokaryotes, Ch 27, U303PP

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Prokaryotes, Ch 27, U303PP
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• Overview Theyre (Almost) Everywhere!
• Most prokaryotes are microscopic
• But what they lack in size they more than make up
  for in numbers
• The number of prokaryotes in a single handful of
  fertile soil
• Is greater than the number of people who have
  ever lived

• Prokaryotes thrive almost everywhere
• Including places too acidic, too salty, too cold,
  or too hot for most other organisms

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• Concept 27.1 Structural, functional, and genetic
  adaptations contribute to prokaryotic success
• Most prokaryotes are unicellular
• Although some species form colonies

Staphylococcus
Legionella
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Classification is difficult in prokaryotes
because they are similar, but we can use certain
morphological and metabolic differences to
classify

• Prokaryotic cells have a variety of shapes
• The three most common of which are spheres
  (cocci), rods (bacilli), and spirals

Figure 27.2ac
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Cell-Surface Structures

• One of the most important features of nearly all
  prokaryotic cells
• Is their cell wall, which maintains cell shape,
  provides physical protection, and prevents the
  cell from bursting in a hypotonic environment

Bacteria do not tolerate dry environments very
well principle behind salting meat to preserve it
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• Using a technique called the Gram stain
• Scientists can classify many bacterial species
  into two groups based on cell wall composition,
  Gram-positive and Gram-negative (peptiodglycan
  content)

Hugely important diagnostic test it can provide
an early guide to appropriate antibiotic therapy
for a patient
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SOME BACTERIA HAVE

• The cell wall of many prokaryotes
• Is covered by a capsule, a sticky layer of
  polysaccharide or protein

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SOME BACTERIA HAVE

• Some prokaryotes have fimbriae and pili
• Which allow them to stick to their substrate or
  other individuals in a colony

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Motility
SOME BACTERIA HAVE

• Most motile bacteria propel themselves by
  flagella
• Which are structurally and functionally different
  from eukaryotic flagella

• In a heterogeneous environment, many bacteria
  exhibit taxis
• The ability to move toward or away from certain
  stimuli

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Internal and Genomic Organization

• Prokaryotic cells
• Usually lack complex compartmentalization

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• Some prokaryotes
• Do have specialized membranes that perform
  metabolic functions

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• The typical prokaryotic genome
• Is a ring of DNA that is not surrounded by a
  membrane and that is located in a nucleoid region

Some species of bacteria Also have smaller rings
of DNA called plasmids
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Reproduction and Adaptation

• Prokaryotes reproduce quickly by binary fission
• They can divide every very quickly, 13 hours or
  less
• And also display relatively high mutation rates
• And they undergo transformation, transduction,
  and conjugation which increases their genetic
  variability

If a single bacterium and all of its progeny
carried out binary fission every 20 minutes,
after 48 hours, there would be
220,000,000,000,000,000,000,000,000,000,000,000,00
0,000,000 bacteria
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Best way to wash your hands?

• Typically, people carry between 10,000 and 10
  million bacteria on each hand.
• We all know the importance of good hand washing
  in reducing harmful microorganisms on the skin,
  but what about those times when there is no
  access to hand washing facilities or not enough
  time to wash thoroughly? Can a hand sanitizer
  (alcohol gel) serve as a suitable alternative to
  hand washing?

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How to hand sanitizers work?

• Convenient and easy to use.
• The majority of hand sanitizers contain ethanol
  or isopropanol, or a combination of these two
  products. Alcohol works immediately and
  effectively to kill bacteria and most viruses.
  Solutions containing 60-95 alcohol are most
  effective.
• Alcohol gels work by stripping away the outer
  layer of oil on the skin, thereby destroying any
  "transient" microorganisms present on the surface
  of the hands. After use, re-growth of bacteria on
  the skin tends to occur slowly, thereby
  effectively keeping "residual" micro-flora that
  reside in deeper layers of skin from coming to
  the surface
• Most brands also contain a moisturizer to
  minimize irritation to the skin.
• To be most effective, a dime-size dollop of
  alcohol gel should be rubbed into the hands for
  30 seconds. If hands are dry after only 10-15
  seconds, it is likely that not enough sanitizer
  was used.

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A substitute for handwashing with soap and water?

• Only in certain circumstances
• If your hands are dirty (soil, etc.), then hand
  sanitizers are far less effective
• Health care workers can use hand sanitizers
  effectively because their hands are not usually
  dirty but may have bacterial from different
  patients (concern about nosocomial infections)
• Food service employees handle proteins, fats,
  possibly fecal contamination which reduce
  effectiveness of hand sanitizing gel. It is
  still recommended by the CDC that these
  individuals use soap and water

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Antimicrobial soaps any better?

• Antimicrobial soaps contain an antiseptic agent
  to help lower the number of microbial flora.
• Triclosan is the most commonly used chemical
  ingredient in antimicrobial soaps. A key factor
  in its effectiveness is that it must be left on
  the skin long enough to work, as in a good 30-45
  second scrub.
• Companies have not published information on what
  combination of triclosan concentrations and
  washing times are most effective, so it is
  difficult to know which brands work best.
• Also, there is concern that use of antimicrobial
  soaps may lead to bacterial resistance. While in
  theory this remains possible, research thus far
  has not found evidence that this is happening.

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At home?

• At home, plain soap and water is adequate for
  most consumer uses. There are situations,
  however, when antiseptic hand products are
  advised. Elaine Larson at the Columbia University
  School of Nursing in New York recommends taking
  the extra precaution of using an alcohol gel or
  antibacterial soap for those in the following
  situations
• Close physical contact with persons at high risk
  for infection (such as newborns, the very old, or
  immunosuppressed)
• Direct physical contact with someone having an
  upper respiratory infection, skin infection or
  diarrhea
• Work settings where infectious diseases are
  commonly transmitted, such as child-care centers,
  preschools, prisons or chronic-care residences.

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The most effective way to protect yourself from
infectious disease
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• Many prokaryotes form endospores
• Which can remain viable in harsh conditions for
  centuries

Clostridium tetani, C. perifringes, C. botulinum
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• Concept 27.2 A great diversity of nutritional
  and metabolic adaptations have evolved in
  prokaryotes

When we consider prokaryotic taxonomy, we find
photosynthetic bacteria scattered among different
groups
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Metabolic Relationships to Oxygen

• Prokaryotic metabolism
• Also varies with respect to oxygen

• Obligate aerobes
• Require oxygen
• Facultative anaerobes
• Can survive with or without oxygen
• Obligate anaerobes
• Are poisoned by oxygen

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Nitrogen Metabolism

• Prokaryotes can metabolize nitrogen
• In a variety of ways
• In a process called nitrogen fixation
• Some prokaryotes convert atmospheric nitrogen to
  ammonia

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• Concept 27.3 Molecular systematics is
  illuminating prokaryotic phylogeny
• Until the late 20th century
• Systematists based prokaryotic taxonomy on
  phenotypic criteria
• Applying molecular systematics to the
  investigation of prokaryotic phylogeny
• Has produced dramatic results immense diversity
  of prokaryotes
• Horizontal gene transfer has complicated our
  molecular understanding (unrelated species have
  freely swapped DNA)

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Lessons from Molecular Systematics

• Molecular systematics
• Is leading to a phylogenetic classification of
  prokaryotes
• Is allowing systematists to identify major new
  clades

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• A tentative phylogeny of some of the major taxa
  of prokaryotes based on molecular systematics

Figure 27.12
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Bacteria

• Diverse nutritional types
• Are scattered among the major groups of bacteria
• For example, photosynthetic bacteria are
  scattered throughout, which suggests either
• Photosynthesis evolved multiple times.
  Parsimonious? No
• Or
• -- Photosynthesis evolved early, then was LOST by
  many groups
• Evidence right now suggests the latter
• The two largest groups are
• The proteobacteria and the Gram-positive bacteria

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2.5 ?m

• Proteobacteria

1 ?m
0.5 ?m
Chromatium the small globules are sulfur wastes
(LM)
5 ?m
10 ?m
Fruiting bodies of Chondromyces crocatus, a
myxobacterium (SEM)
Bdellovibrio bacteriophorus Attacking a larger
bacterium (colorized TEM)
2 ?m
Figure 27.13
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• Chlamydias, spirochetes, Gram-positive bacteria,
  and cyanobacteria

2.5 ?m
Chlamydia (arrows) inside an animal cell
(colorized TEM)
5 ?m
Leptospira, a spirochete (colorized TEM)
1 ?m
5 ?m
Hundreds of mycoplasmas covering a human
fibroblast cell (colorized SEM)
Streptomyces, the source of many antibiotics
(colorized SEM)
50 ?m
Two species of Oscillatoria, filamentous
cyanobacteria (LM)
Figure 27.13
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Archaea

• Archaea share certain traits with bacteria
• And other traits with eukaryotes

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• Some archaea
• Live in extreme environments
• Extreme thermophiles
• Thrive in very hot environments

• Methanogens
• Live in swamps and marshes
• Produce methane as a waste product

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• Extreme halophiles
• Live in high saline environments

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• Concept 27.4 Prokaryotes play crucial roles in
  the biosphere
• Prokaryotes are so important to the biosphere
  that if they were to disappear
• The prospects for any other life surviving would
  be dim

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Chemical Recycling

• Prokaryotes play a major role
• In the continual recycling of chemical elements
  between the living and nonliving components of
  the environment in ecosystems

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• Chemoheterotrophic prokaryotes function as
  decomposers
• Breaking down corpses, dead vegetation, and waste
  products
• Nitrogen-fixing prokaryotes
• Add usable nitrogen to the environment

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Symbiotic Relationships

• Many prokaryotes
• Live with other organisms in symbiotic
  relationships such as mutualism and commensalism

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• Other types of prokaryotes
• Live inside hosts as parasites

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• Concept 27.5 Prokaryotes have both harmful and
  beneficial impacts on humans
• Some prokaryotes are human pathogens
• But many others have positive interactions with
  humans

Harmless and beneficial bacteria far outnumber
harmful varieties. Because they are capable of
producing so many enzymes necessary for the
building up and breaking down of organic
compounds, bacteria are employed extensively by
humansfor soil enrichment with leguminous crops
(nitrogen cycle) for preservation by pickling,
for fermentation (as in the manufacture of
alcoholic beverages, vinegar, and certain
cheeses), for decomposition of organic wastes (in
septic tanks, in some sewage disposal plants, and
in agriculture for soil enrichment) and toxic
wastes, and for curing tobacco, retting flax, and
many other specialized processes. Bacteria
frequently make good objects for genetic study
large populations grown in a short period of time
facilitate detection of mutations.
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Pathogenic Prokaryotes

• Prokaryotes cause about half of all human
  diseases
• Lyme disease is an example

Staph infection
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Among the prokaryotic diseases

• Tooth decay
• Cholera
• Leprosy
• Tetanus
• Some forms of pneumonia
• Whooping couch
• Diphtheria
• Tuberculosis
• Some STDs
• Forms of food poisoning
• Wound infections

15 million NEW cases each year
80 million cases each year
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• Pathogenic prokaryotes typically cause disease
• By releasing exotoxins or endotoxins
• Many pathogenic bacteria
• Are potential weapons of bioterrorism

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Prokaryotes in Research and Technology

• Experiments using prokaryotes
• Have led to important advances in DNA technology

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• Prokaryotes are the principal agents in
  bioremediation
• The use of organisms to remove pollutants from
  the environment

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• Prokaryotes are also major tools in
• Mining
• The synthesis of vitamins
• Production of antibiotics, hormones, and other
  products