Prokaryotes and the Origins of Metabolic Diversity

1
Prokaryotes and the Origins of Metabolic Diversity

• Chapter 27

2
Prokaryotes vs. Eukaryotes

• Prokaryotes DO NOT have a nucleus or
  membrane-bound organelles while Eukaryotes have
  both
• Biomass of Prokaryotes outweighs all eukaryotes
  by at least ten-fold

3
Figure 27.4x2 Prokaryotes and eukaryotic cell
4
Prokaryotes are not all bad

• Many do cause disease, but others are symbiotic
  (E. coli in intestines), help with cycling
  nutrients (decomposers and carbon cycle)
• Are about 5,000 species known, could be as many
  as 4 million

5
5 kingdoms vs. 3 domains for classification

• 5 kingdoms Monera, Protista, Fungi, Plantae,
  Animalia
• this scheme emphasizes the structural
  differences between prok and euk
• but, a single kingdom does not reflect
  evolutionary history seem to be two major
  branches of prok evolution
• 3 Domains Bacteria, Archaea, Eukarya
• shows early divergence in types of bacteria

6
Figure 27.2 The three domains of life
7
See page 537
8
Structure of Prokaryotes Groups, shape, and
size range

• Most are unicellular, but some may aggregate in
  groups of two or more
• Others are true colonies permanent aggregates
  of identical cells chains (strepto)
• clusters (staphalo)
• Differ in shape 3 most common
• spherical (coccus or cocci)
• rod-like (bacillus or bacilli)
• helical (spirillum or spirilla, spirochetes)
• Diameter ranges between 1-5 um largest is .75 mm
  in diameter (Thiomargarita namibiensis)

9
Figure 27.0 Bacteria on the point of a pin
10
Figure 27.3 The most common shapes of prokaryotes
11
Figure 27.4 The largest known prokaryote
12
Structure

• Has a cell wall which
• maintains shape of cell
• affords physical protection
• prevents cell from bursting in hypotonic
  conditions
• (BUT, bacteria will also plasmolyze and
  die in hypertonic conditions, so ex.,
  salted meat keeps)

13
Domain Bacteria vs. Archaea

• cell walls of bacteria contain peptidoglycan
  
• consists of polymers of modified sugars
  cross-linked by short polypeptides that vary
  from bacterial species to species this gives a
  single molecular network enclosing and
  protecting the entire cell.
• Walls of archaea lack peptidoglycan

14
Identification of Bacteria

• Culture area affected throat w/ giant swab
• Grow suspected pathogen on petri dish
• Isolate the org (if are several present) by using
  STREAKING technique
• first pass on petri is all pathogens
• flame tip of innoculation loop
• make second pass at 90 degree angle through
  first set
• flame tip of innoculation loop
• make third pass at 90 degree angle through
  second set
• Last colonies streaked should be most pure

15
Figure 27.9x Bacterial and fungal colonies
16
Figure 27.9 Prokaryote colonies in culture
17
Identification of Bacteria

• Use Kochs Postulates to identify pathogen
• a. Isolate org suspected of causing illness
• (using streaking technique) in several
  diseased individuals
• b. Grow org in lab culture
• c. Innoculate a healthy animal with the
  cultured org, see if animal contracts
  illness induce disease in new host
• d. If illness occurs, re-isolate the org that
  caused the disease
• e. repeat and retest the org

18
Gram staining

• Adds dye to bacteria way stains is indication
  of bacterial type (structure)
• Gram positive stains PURPLE has simple, thick
  cell wall made of polysaccharides
• Gram negative stains PINK has a protective
  outer cell membrane, and has less peptidoglycan
  in cell walls are structurally more complex
  (contain lipopolysaccharides that are often toxic
  to host)
• negatives are more resistant to antibiotics

19
Figure 27.5 Gram-positive and gram-negative
bacteria
20
Figure 27.5x Gram-positive and gram-negative
bacteria
21
If bacteria can be treated

• Grow bacteria into lawn on petri dish
• Drop different types of antibiotics at different
  locations on lawn
• Many antibiotics inhibit the synthesis of
  cross-links in peptidoglycan and prevent the
  formation of a functional wall, so can look for
• formation of plaques areas where bacteria
  have died
• Large, clear plaques are best if see a halo
  effect, some of the bacteria are resistant, not a
  good antibiotic to use against that bacteria

22
Other protective coverings

• Slime capsule secretions that allow bacteria to
  adhere to a substrate and to hold on in colonies
• Pili surface appendages that hold on to
  substrates may even assist in conjugation (DNA
  transfer between bacteria)

23
Figure 27.6 Pili
24
Figure 27.x1 Prokaryotic conjugation
25
Mobility in prokaryotes

• In a uniform environment, movements may be random
• Use of flagella is most common type of propulsion
• May be scattered over the entire cell surface
  or concentrated on one or both ends of the cell
• Prokaryotic flagella are smaller than that of
  eukaryotes, and are not covered by cell
  membrane
• Spirochetes have cork-screw movement due to
  helical filaments under the outer layer of the
  cell wall
• Some secrete slimy threads and glide along

26
Figure 27.7 Form and function of prokaryotic
flagella
27
Figure 27.x3 Prokaryotic flagella (Bacillus)
28
Figure 27.x2 Prokaryotic flagella (A. serpens)
29
Figure 27.x1 Prokaryotic flagella
30
Taxis

• Def Movement toward or away from a stimulus
• can be a positive or negative taxis
• Ex. Toward food, positive chemotaxis
• Away from toxin, negative chemotaxis
• Many prokaryotes are capable of this in
  heterogeneous environments
• May even have special devices that allow for
  response (Ex. magnetic particles that allow for
  orientation to Earths magnetic field know up
  from down, so go to nutrient-rich sediment at
  bottom of ponds)

31
Genomic organization in Prokaryotes

• Prok genomes are smaller, simpler than Eukaryotic
  genomes (P have 1/1000th as much DNA as E)
• DNA is concentrated as a snarled fiber in a
  nucleiod region (is no nucleus) with very little
  protein present referred to as a genophore
• Along with DNA, prok may have plasmids smaller
  rings of DNA that endow the cell with
• resistance to antibiotics
• metabolism of unusual nutrients

32
Growth and adaptation

• Prok reproduce asexually by binary fission
• NO MITOSIS OR MEIOSIS OCCURS!!!
• May transfer genes between individuals, though,
  using 3 methods
• a. transformation prok cell takes up genes
  from surrounding environ
• b. conjugation direct transfer of genes from
  one prok to another (through tube)
• c. transduction viruses transfer genes
  between prok
• All three methods are unilateral passage of
  variable amount of DNA

33

• Mutation is major source of genetic variation in
  prok
• Generation times are short minutes or hours
  so favorable mutations can be rapidly propagated
  in offspring
• Reproduction is geometric 1 divides into 2, 2
  divide into 4, 4 divide into 8, etc.

34
If conditions are not suitable for reproduction

• Some bacteria may form endospores resistant
  cells where original cell replicates its
  chromosome, and one copy becomes surrounded by a
  durable wall outer well disintegrates, leaving
  the highly resistant endospore capsule

35
Figure 27.10 An anthrax endospore
36
Figure 27.10x Endospores
37
Nutritional Diversity

• Nutrition of prok how org obtains energy and a
  carbon source to build org molecules
• Are 4 categories
• a. photoautotrophs
• b. chemoautotrophs
• c. photoheterotrophs
• d. chemoheterotrophs

38
Photoautotrophs

• Photosynthetic
• Harness light energy to make organic compounds
  from CO2
• Ex. cyanobacteria

39
Figure 27.11 One of the most independent
organisms on earth Cyanobacteria (Anabaena)
40
Figure 27.11x1 Cyanobacteria Gloeothece (top
left), Nostoc (top right), Calothrix (bottom
left), Fischerella (bottom right)
41
Chemoautotrophs

• Need only CO2 as carbon source
• Oxidize inorganic substances to get energy
• Chemical energy is extracted from H2S, NH3, Fe2,
  etc.

42
Photoheterotrophs

• Use light to generate ATP but must get carbon in
  organic form

43
Chemoheterotrophs

• Must consume organic molecules for energy and
  carbon
• Very common in prokaryotes
• Ex.
• saprobes decomposers that absorb nutrients
  from dead organic matter
• parasites absorb nutrients from body fluids
  of living hosts

44
Table 27.1 Major Nutritional Modes
45
Nitrogen metabolism

• Nitrogen fixation some prokaryotes convert
  atmospheric nitrogen (N2) to ammonium (NH4)
• Is the only biological mechanism that makes
  atmospheric nitrogen available to other orgs for
  incorporation into organic compounds (namely,
  proteins and nucleic acids)
• Prok that do this are very self-sufficient need
  only light energy, CO2, N2, water, and some
  minerals in order to grow

46
Metabolic relationships to oxygen

• 3 categories
• a. obligate aerobes must have O2
• b. facultative anaerobes will use O2 if it
  is present but grow by fermentation in an
  anaerobic environ
• c. obligate anaerobes poisoned by O2

47
See pages 538 and 539 for five major clades of
bacteria

• Proteobacteria
• Chlamydias
• Spirochetes
• Gram-positive bacteria
• Cyanobacteria
• be familiar with general characteristics

48
Ecological Impact of Prokaryotes

• Indispensable links in recycling of nutrients
  (decomposers)
• Symbiotic relationships interact with other
  orgs and form food webs
• Cause many diseases
• opportunisitic (normal residents, but cause
  disease when immune system is weak)
• Bioremediation use or orgs to remove pollutants
  from water, air, and soil
• Ex. Sewage treatment plants anaerobic prok
• Ex. Decompose petroleum compounds at oil spills
  -- pseudomonads
• Act as metabolic factories for human use
• -produce acetone, butanol
• -make vitamins, antibiotics
• -food flavorings (yogurt, cheese)
• -DNA technology produce hormones like insulin