How do Archaea tolerate the heat?

1
How do Archaea tolerate the heat?

• Proteins stabilized by more ionic bridges between
  amino acid r-groups and more-hydrophobic core
  amino acids
• Heat shock protein (chaperonins) refold denatured
  proteinsPyrococcus 121C for 1 hour!
• DNA depurination reduced by presence of
  2,3-diphosphoglycerate.
• DNA supercoiling by reverse gyrase reduces
  denaturation
• Sac7d in Sulfobolus is a minor groove protein
  increases the melting temperature by 40C
• Histone-like proteins help stabilize DNA as well
• Heat-resistant di-bi-phytanyl diether lipid
  membranes (monolayer) prevent delamination of
  membrane

2
Cell Membrane Structure
Composed of diglycerides R group may be
phosphate, sulfate, or sugar Long chain branched
hydrocarbon (not fatty acid) Hydrocarbons may be
C20 or C40 If C20, the membrane is a bilayer
If C40, the membrane is a monolayer
In some species, the membrane is a mixture of
both C20 and C40 diglycerides forming a mixed
mono-/bi-layer
3
Cell Structure Movement
hook
directional rotation?
basal rings and rod
anchorage rotation
stiff helical flagellum
flagellin protein
is rotated by motor apparatus in the membrane
by H ATPase at rates of 200-1700 rps
(gt12,000 rpm!)
Taxis movement toward stimulus
Motile Archaea often have multiple flagella in a
tuft at one place on the cell surface
phototaxis movement toward light
chemotaxis movement to chemicals
thermotaxis movement to heat
4
Cell Structure Nucleoid
Nucleoid - genome
one circular DNA molecule plasmids histone-like
protein association (eukaryotic) genome smaller
than typical bacteria sequences closer to
eukaryotic homologs introns in rRNA and tRNA
genes operon regulation in some genes like
bacteria attached to cell membrane
transcription by RNA polymerase (POLII_at_TATA)
replication by DNA polymerase
separation of chromosomes
cytokinesis by furrowing
70S Ribosome

• Process called binary fission
• NOT mitosis!
• Genome and copy are identical
• Genome is haploid
• There is no synapsis
• There is no recombination

rRNA protein ribozymes
translation of mRNA into protein
5
Cell Structure Genetic Structure
Nucleoid - main chromosome is circular but
associated with histone-like proteins
Replicons - small circular DNAs with additional
essential genes

• Genes are generally in clusters in operon-like
  situations
• Chromosomes have insertion sites for
  transposition events
• rRNA and other genes have intron sequences
• How the movements of the multiple units is
  coordinated is not yet fully known

6
3 chromosomes Main chromosome 2,015 kb 191 kb
replicon 366 kb replicon Replicons have genes
for DNA polymerase Transcription factors Mineral
uptake (K, PO4) Cell division The genome has many
insertion sites for foreign genes Bacteriorhodop
sin Protein retinal Amax 280 UV, 570 green
nm energy for proton transport and
phosphorylation without photosynthesis!
Halobacterium salinarium
http//biology.kenyon.edu/Microbial_Biorealm/ arch
aea/halobacterium/halobacteria_1.jpg
Aerobic Respiration Up to 5 M (25 NaCl)! Great
Salt Lake, Utah Red Sea, Asia Minor
7
Periplasmic space
Cell Membrane
Retinal
lsu.epfl.ch/sh/bR_full.pdf
Cytoplasm
Bacteriorhodopsin absorbs green from the visible
spectrum, so what color is the pigment?
Hint it reflects the other colors of the spectrum
www.hawaii.edu/microbiology/ Alam/publications/PNA
S96-ZHANG.pd
8
Which of these metabolic pathways is
Halobacterium demonstrating?

• Photoautotrophism
• Photoheterotrophism
• Chemoautotrophism
• Chemoheterotrophism

v

• Hint
• Light for energy
• Chemicals for carbon

9
Methanococcus jannischii
Isolated from white smoker hydrothermal
vent 2600m deep on the East Pacific
Rise Methanogen Obligate anaerobe H2 as energy
source CO2 as carbon source CH4 as byproduct of
metabolism Temperature 50-86C Other species
found in cow rumen (first stomach) Cow belches 50
L of methane per day
http//www.bact.wisc.edu/Bact303/Methanococcus.jpe
g
What does this electron micrograph tell
you? about cell shape? about motility?
10
Which of these metabolic pathways is
Methanococcus demonstrating?

• Photoautotrophism
• Photoheterotrophism
• Chemoautotrophism
• Chemoheterotrophism

v

• Hint
• H2 for energy
• CO2 for carbon

11
Thermus aquaticus
Gram negative Thermophile isolated from
Yellowstone Hot Spring Optimum temperature
85C Stability of macromolecules
excellent Enzymes for research or commercial
use Taq polymerase is the enzyme of PCR
(Polymerase Chain Reaction) Lives near
cyanobacteria which feed Thermus
http//www.molgen.mpg.de/ag_ribo/ ag_franceschi/f
ranceschi-projects-30S.html
http//sci.agr.ca/crda/images/BACTERI1.JPG
12
Which of these metabolic pathways is Thermus
demonstrating?

• Photoautotrophism
• Photoheterotrophism
• Chemoautotrophism
• Chemoheterotrophism

v

• Hint
• Organic chemicals for energy
• Organic chemicals for carbon

13
Sulfolobus acidocaldarius
75C Optimum Strict aerobe pH 1 to 6 Oxidize
Sulfur or can use Fe2 or MnO42- as electron
acceptorsuses glycolysis and TCA cycle Pilus
and conjugation plasmids not similar to bacterial
ones
http//dac.molbio.ku.dk/Sulfolobus.jpg
14
Which of these metabolic pathways is Sulfolobus
demonstrating?

• Photoautotrophism
• Photoheterotrophism
• Chemoautotrophism
• Chemoheterotrophism

v

• Hint
• Organic chemicals for energy
• Organic chemicals for carbon