An Overview of Microbial Life
Chapter 2
Elements of Cell and Viral
Structures:
„
„
„
„
3 Domains: Archae, Eubacteria, Eukaryota
Two structural types of cells are recognized:
the prokaryote and the eukaryote.
Prokaryotic cells have a simpler internal
structure than eukaryotic cells, lacking
membrane-enclosed organelles.
Viruses:
– Viruses are not cells but depend on cells for their
replication.
Cells from each domain
Eukarya
Bacteria
Archae
The basic components..
components
„
All microbial cells share
certain basic structures in
common, such as
cytoplasm a cytoplasmic
cytoplasm,
membrane, ribosomes,
and (usually) a cell wall.
– Note
Note: Animal cells typically
t picall
do not have a cell wall
„
The major components
dissolved in the cytoplasm
include
– Macromolecules
– Inorganic
I
i ions
i
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E kar otic Cells
Eukaryotic
„
„
„
Larger and structurally
more complex
Euk microorganisms
Euk.
include algae, fungi and
protozoa
M b
Membrane
enclosed
l
d
organelles
– Nucleus
– Mitochondria
– Chloroplasts
(photosynthetic cells
only)
Prokar otic Cells
Prokaryotic
„
„
„
„
Lack
L
k membrane
b
enclosed
l
d organelles
ll
Include Bacteria and Archae
Smaller than eukaryotic cells (Typically ~1-5
~1 5
um long and ~1um in width)
However, can varyy g
greatly
y in size
Viruses
„
„
„
Not cells
Static structures which
rely on cells for
replication
li ti and
d
biosynthetic machinery
Many cause disease
and can have profound
effects on the cells they
infect
– Cancer, HIV
„
However, can alter
genetic material and
improve the cell
Arrangement
g
of DNA in
Microbial Cells
„
„
„
Genes govern the properties of cells, and a
cell's complement of genes is called its
genome.
DNA is arranged in cells to form
chromosomes.
h
In prokaryotes, there is usually a single
circular
i l chromosome;
h
whereas
h
iin
eukaryotes, several linear chromosomes
exist.
exist
Nucleus vs.
vs Nucleoid
„
„
Nucleus: a membrane
membraneenclosed structure that
contains the
chromosomes in
eukaryotic cells.
Nucleoid: aggregated
mass of DNA that
constitutes the
chromosome
h
off cells
ll off
Bacteria and Archaea
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i t
Prokar otic DNA
Prokaryotic
„
Most DNA is circular
„ Most have only
y a single
g chromosome
„ Single copy of genes
– Haploid
„
Many also contain plasmids
Plasmids
„
„
„
Plasmids are circular
extrachromosomal
genetic elements (DNA)
(DNA),
nonessential for growth,
found in prokaryotes.
Typically contain genes
that confer special
properties (ie unique
metabolic properties)
Useful in biotechnology
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E kar otic DNA
Eukaryotic
„
Organized into linear molecules
„ Packaged into chromosomes
– Number varies
„
Typically contain two copies of each
gene
– Diploid
Di l id
Genes genomes,
Genes,
genomes and proteins
„
E.coli genome= a single circular
chromosome of 4.68 million base pairs
„ # of genes: 4,300
„ A single
g cell contains:
– 1,900 different proteins
– 2.4 million p
protein molecules
– Abundance of proteins varies
Genome size,
size complexity,
complexity and
the C-value paradox
p
„
Genome size does
not necessarily
correlate with
organismal
i
l
complexity
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In actuality….
act alit
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The Tree of Life
„
Evolution: change in allelic
frequencies
q
over g
generations
„ The evolutionary relationships between
life forms are the subject of the science
of phylogeny.
„ Phylogenetic relationships are deduced
by comparing ribosomal sequences
The three domains of life
„
Comparative ribosomal RNA sequencing has
defined the three domains of life: Bacteria,
Archaea,, and Eukarya.
y
What has this sequencing
q
g
revealed??
„
„
Molecular sequencing has shown that the
major organelles of Eukarya have
evolutionary roots in the Bacteria
Mitochondria and chloroplasts were once
f
free-living
li i cells
ll th
thatt established
t bli h d stable
t bl
residency in cells of Eukarya eons ago.
– The process by which this stable arrangement
developed is known as endosymbiosis.
What has this sequencing
q
g
revealed?? Cont.
„
Although species of Bacteria and
Archaea share a p
prokaryotic
y
cell
structure, they differ dramatically in their
y history.
y
evolutionary
„ Archae are more closely related to
eukaryotes than are species of bacteria
Molecular sequencing
q
g and
microbiology
„
Overall rRNA sequencing technology has
helped reveal the overall evolutionary
connections between all cells
– In particular prokaryotes
„
Impacted subdispiciplines
– Microbial classification and ecology
– Clinical diagnostics
„
Can identify organisms without having to
culture them
Microbial Diversity
„
Cell size and morphology
„ Metabolic strategies (physiology)
„ Motility
„ Mechanisms of cell division
„ Pathogenesis
„ Developmental biology
„ Adaptation to environmental extremes
„ And many more
Physiological Diversity of
Microorganisms
„
„
All cells
ll need
d carbon
b and
d energy
sources
Energy can be obtained in 3
ways:
– Organic chemicals
– Inorganic
g
chemicals
– Light
„
Types of physiological diversity:
–
–
–
–
–
Chemoorganotrophs
Chemolithotrophs
Phototrophs
Heterotrophs and Autotrophs
Habitats and Extreme environments
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Chemoorganotrophs
„
Chemoorganotrophs obtain their energy
from the oxidation of organic compounds.
– Energy
E
conserved
d as ATP
„
„
„
„
All natural and even synthetic organic
compounds can be used as an energy source
Aerobes
Anaerobes
Most microorganisms that have been cultured
are chemoorganotrophs
Chemolithotrophs
„
Chemolithotrophs obtain their energy
from the oxidation of inorganic
compounds.
„ Found only in prokaryotes
„ Can use a broad spectrum of inorganic
compounds
„ Advantageous because can utilize
waste products of chemoorganotrophs
Phototrophs
„
Phototrophs
p contain p
pigments
g
that allow
them to use light as an energy source.
– ATP generated from light energy
– Cells
C ll are colored
l d
„
Oxygenic photosynthesis:
– O2 involved
– Cyanobacteria and relatives
„
Anoxygenic
yg
p
photosynthesis:
y
– No O2
– Purple and green bacteria
A totrophs and Heterotrophs
Autotrophs
„
„
All cells require
req ire carbon as a major n
nutrient
trient
Microbial cells are either:
–A
Autotrophs
t t
h use carbon
b di
dioxide
id as th
their
i carbon
b
source, whereas heterotrophs use organic
carbon from one or more organic compounds.
– Autotrophs considered primary producers
• Synthesize organic matter from CO2 for themselves and
that of chemoorganotrophs
• All organic matter on earth has been synthesized from
primary producers
Habitats and Extreme
Environments
„
„
Microorganisms are everywhere on Earth
that can support life
Extremophiles: organisms inhabiting
extreme environments
– Boiling
g hot springs,
p g ,
– Within ice, extreme pH, salinity, pressure
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E amples of Extremophiles:
Examples
E tremophiles:
Prokaryotic Diversity
„
Several lineages are present in the
domains Bacteria and Archaea
„ An enormous diversity of cell
morphologies and physiologies are
represented
„ rRNA analysis has shown dramatic
differences in phenotypic characteristics
within a given phylogenetic group
Bacteria
Proteobacteria
„
„
„
„
The Proteobacteria is the largest
g
division
(called a phylum) of Bacteria
A major lineage of bacteria that contains a
l
large
number
b off gram(-)
( ) rods
d and
d coccii
Represent majority of known gram(-) medical,
industrial and agricultural bacteria of
industrial,
significance
Extreme
t e e metabolic
etabo c d
diversity:
e s ty
–
–
–
–
Chemorganotrophs: E.coli
Photoautotrophs: Purple sulfur bacterium
Chemolithotrophs: Pseudomonas, Aztobacter
Pathogens: Salmonella, Rickettsia, Neisseria
Proteobacteria examples
e amples
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Chemolithotrophic sulfur-oxidizing
bacteria Achromatium
Neisseria gonorrhoeae
Gram-positive
Gram
positive bacteria
„
„
„
United by a common cell wall structure
Examples:
Spore forming:
– Clostridium, Bacillus
„
Antibiotic producing:
– Streptomyces
„
Lactic acid bacteria:
– Streptococcus
– Lactobacillus
„
Mycoplasmas:
– Lack cell wall
– Small genomes
– Often pathogenic
Cyanobacteria
„
„
The Cyanobacteria
are phylogenetic
relatives of grampositive bacteria and
are oxygenic
phototrophs.
First oxygenic
phototrophs to have
evolved
e
o ed o
on Earth
a
Planctom ces
Planctomyces
„
„
Characterized by
distinct cells with
stalks that allow for
attachment to solid
surfaces
Aquatic
Spirochetes
„
„
„
Helical shaped
Morphologically and
phylogenetically
h l
ti ll
distinct
Widespread in
nature and some
cause disease
– Most notable sp
cause Syphilis and
Lyme Disease
Spirochaeta zuelzerae
Green sulfur and non-sulfur
bacteria
„
„
„
Contain similar
photosynthetic
pigments
Can grow as autotrophs
Chloroflexus
– IInhabits
h bi h
hot springs
i
and
d
shallow marine bays
– Dominant organism in
stratified microbial mats
– Important link in the
evolution of
p
photosynthesis
y
Chlam dia
Chlamydia
„
„
„
Most species are
pathogens
Obligate intracellular
parasites
How would this
affect an immune
response?
?
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i
Deinococc s
Deinococcus
„
„
„
Contain sp with
unusual cell walls
and high level of
resistance to
radiation
Cells usually exist in
pairs or tetrads
Can reassemble its
chromosome after
high radiation
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Aq ife Thermotoga,
Aquifex,
Thermotoga Env-OP2
En OP2
„
„
„
Sp that branch early
on the tree
Unified in that they
grow at very high
temps:
hyperthermophily
I h bit t off hot
Inhabitats
h t
springs
Archaea
„
„
„
There are two lineages
of Archaea: the
Euryarchaeota and the
Crenarchaeota
Many are extremophiles
All are chemotrophic
h
t hi
– Many using organic
carbon
– While
Whil others
th
are
chemolithotrophs
E r archaeota & Crenarchaeota
Euryarchaeota
„
„
Physiologically diverse
groups
Many inhabit extreme
environments
– From extreme pH,
temperature, salinity
Limitations of Phylogenetic
y g
analyses
„
Not all Archaea are extremophiles
„ Difficult to culture
„ Based on molecular microbial ecology,
the extent of diversity is much greater
than once thought
Eukaryotic Microorganisms
„
„
„
„
Collectively, microbial eukaryotes are known
Collectively
as the Protista.
Microbial eukaryotes
y
are a diverse g
group
p that
includes algae, protozoa, fungi, and slime
molds
C ll off algae
Cells
l
and
d ffungii h
have cellll walls,
ll
whereas the protozoa do not.
The “early-branching”
early branching Eukarya are
structurally simple eukaryotes lacking
mitochondria and other organelles
– Ex Giardia
Eukaryotic microbial diversity
Eukaryotic microbial diversity
„
Diplomonads: flagellates, many are parasitic
– Ex: Giardia lamblia ((synonymous
y
y
with Lamblia
intestinalis and Giardia duodenalis) is a
flagellated protozoan parasite flagellated
protozoan p
p
parasite
„
Trichomonads: anaerobic protist, many are
pathogenic
– Ex. Trichomonas vaginalis
„
Flagellates: all protozoa in this group utilize
flagella for motility
motility, free-living
free-living, and pathogenic
– Ex. Trypanosomes
„
Slime molds: resemble fungi
g and p
protozoa
– Ex. Dictyostelium discoideum
Fungi
Protozoa
Algae
Lichens
„
Some algae and
fungi have
developed
mutualistic
associations called
lichens.
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