Diversity of
Microbial World
Madam Noorulnajwa Diyana
Yaacob
PPK BIOPROSES
April/May 2013
Course content
 Prokaryotes
Archaea
Bacteria
 Eukaryotes
(microbial Protists)
Fungi
Algae
Protozoa
 Viruses
Introduction

Taxonomy is the science of the
classification of organisms, with the goal of
showing relationships among organisms.

Taxonomy also provides a means of
identifying organisms.
 consists
of three separate but interrelated
parts
classification – arrangement of organisms into
groups (taxa; s., taxon)
 nomenclature – assignment of names to taxa
 identification – determination of taxon to which an
isolate belongs

How would you classify?
Types of classification:
1. natural
2. polyphasic
 phenetic
 phylogenetic
 genotype
Natural Classification

arranges organisms into groups whose
members share many characteristics

first such classification in 18th century
developed by Linnaeus


based on anatomical characteristics
this approach to classification does not
necessarily provide information on
evolutionary relatedness
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Polyphasic Taxonomy
used to determine the genus and
species of a newly discovered
prokaryote
 incorporates information from genetic,
phenotypic, and phylogenetic analysis

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Phenetic Classification

groups organisms together based on
mutual similarity of phenotypes (is the
composite of an organism's observable characteristics or traits,
such as its morphology, development, biochemical or
physiological properties, phenology, behavior, and products of
behavior)

can reveal evolutionary relationships,
but not dependent on phylogenetic
analysis
 i.e.,

doesn’t weigh characters
best systems compare as many
attributes as possible
8
Phylogenetic Classification
also called phyletic classification
systems
 phylogeny

 evolutionary

development of a species
usually based on direct comparison of
genetic material and gene products
 Woese
and Fox proposed using small
subunit (SSU) rRNA nucleotide sequences
to assess evolutionary relatedness of
organisms
9
Genotypic Classification

comparison of genetic (inherited
instructions it carries within its genetic
code) similarity between organisms
 individual
genes or whole genomes can be
compared
 70% homologous belong to the same
species
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Taxonomic Ranks - 1
microbes are placed in hierarchical
taxonomic levels with each level or rank
sharing a common set of specific
features
 highest rank is domain

and Archaea – microbes only
 Eukarya – microbes and macroorganisms
 Bacteria

within domain
 phylum,
class, order, family, genus, species
epithet, some microbes have subspecies
11
Species

definition
 collection
of strains that share many stable
properties and differ significantly from other
groups of strains

also suggested as a definition of species
 collection
of organisms that share the same
sequences in their core housekeeping
genes
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Strains
descended from a single, pure microbial
culture
 vary from each other in many ways

– differ biochemically and
physiologically
 morphovars – differ morphologically
 serovars – differ in antigenic properties
 biovars
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Type Strain
usually one of first strains of a species
studied
 often most fully characterized
 not necessarily most representative
member of species

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Genus
well-defined group of one or more strains
 clearly separate from other genera
 often disagreement among taxonomists
about the assignment of a specific species
to a genus

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Binomial System of Nomenclature


devised by Carl von Linné (Carolus Linnaeus)
each organism has two names
name – italicized and capitalized (e.g.,
Escherichia)
 species epithet – italicized but not capitalized (e.g.,
coli)
 genus


can be abbreviated after first use (e.g., E. coli)
a new species cannot be recognized until it has
been published in the International Journal of
Systematic and Evolutionary Microbiology
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Techniques for Determining Microbial
Taxonomy and Phylogeny

classical characteristics
morphological
physiological
biochemical
ecological
genetic
Ecological Characteristics
life-cycle patterns
 symbiotic relationships
 ability to cause disease
 habitat preferences
 growth requirements

Molecular Approaches
extremely important because almost no
fossil record was left by microbes
 allows for the collection of a large and
accurate data set from many organisms
 phylogenetic inferences based on these
provide the best analysis of microbial
evolution currently available

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Molecular Characteristics
nucleic acid base composition
 nucleic acid hybridization
 nucleic acid sequencing
 genomic fingerprinting
 amino acid sequencing

Nucleic Acid Base Composition

G + C content
 Mol%
G+C=
(G + C/G + C + A + T)100
 usually determined from melting
temperature (Tm)
 variation within a genus usually <10%
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Figure 17.2
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Nucleic Acid Hybridization

DNA-DNA hybridization
 measure

of sequence homology
common procedure
 bind
nonradioactive DNA to nitrocellulose
filter
 incubate filter with radioactive singlestranded DNA
 measure amount of radioactive DNA
attached to filter
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Table 17.4
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Nucleic Acid Sequencing

Small subunit rRNAs (SSU rRNAs)
 sequences
of 16S and 18S rRNA most
powerful and direct method for inferring
microbial phylogenies and making
taxonomic assignments at genus level
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Comparative Analysis of 16S
rRNA Sequences

oligonucleotide signature sequences found
 short
conserved sequences specific for a
phylogenetically defined group of organisms


either complete or, more often, specific rRNA
fragments can be compared
when comparing rRNA sequences between 2
organisms, their relatedness is represented
by percent sequence homology
 70%
is cutoff value for species definition
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Figure 17.3
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Genomic Fingerprinting
used for microbial classification and
determination of phylogenetic
relationships
 requires analysis of genes that evolve
more quickly than rRNA encoding
genes

 multilocus

the sequencing and comparison of 5 to 7
housekeeping genes is done to prevent
misleading results from analysis of one gene
 multilocus

sequence analysis (MSLA)
sequence
typing (MLST) –
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among
reproduction orstrains
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Restriction Fragment Length
Polymorphism (RFLP)

uses restriction enzymes to recognize
specific nucleotide sequences
 cleavage

patterns are compared
ribotyping
 similarity
between rRNA genes is determined
by RFLP rather than sequencing
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Figure 17.4
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Single Nucleotide Polymorphism
(SNP)
Looks at single nucleotide changes, or
polymorphisms, in specific genes
 16S rRNA focuses on one specific gene
 Regions targeted because they are
normally conserved, so single changes
in a base pair reveal evolutionary
change

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Figure 17.5
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Amino Acid Sequencing



amino acid sequences reflect mRNA
sequence and therefore of the gene which
encodes that protein
amino acid sequencing of proteins such as
cytochromes, histones, and heat-shock
proteins has provided relevant taxonomic and
phylogenetic information
cannot be used for all proteins because
sequences of proteins with different functions
often change at different rates
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Figure 17.6
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The prokaryotes:
Domain Archaea
and
Domain Bacteria
Bergey’s Manual of Systematic
Bacteriology

1923,David Bergey (prof of bacteriology)
published a classification of bacteria for
identification of bacterial (and archaea) species.

Bergey’s Manual categorizes bacteria into taxa
based on rRNA sequences.

Bergey’s Manual lists identifying characteristics
such as Gram stain reaction, cellular
morphology, oxygen requirements, and
nutritional properties.
The Archaea
Archaea





Scientist identified archaea as a distinct type of
prokaryotes based on its unique rRNA sequence
Reproduce by : binary fusion, budding or
fragmentation
Cells shape : cocci, bacilli, spiral, lobed, cuboidal
etc
Not causing disease to humans/animals
Cell wall contain proteins, glycoproteins,
lipoproteins, polysaccharides
Archaeal Cell Surfaces

cell envelopes
 varied
S layers attached to plasma
membrane
 pseudomurein (peptidoglycan-like polymer)
 complex polysaccharides, proteins, or
glycoproteins found in some other species
 only Ignicoccus has outer membrane

flagella closely resemble bacterial type
IV pili
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Archaeal Membrane Lipids
differ from Bacteria and Eukarya in
having branched chain hydrocarbons
attached to glycerol by ether linkages
 polar phospholipids, sulfolipids,
glycolipids, and unique lipids are also
found in archaeal membranes

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Archaeal Lipids and Membranes
Bacteria/Eukaryote
s
 fatty acids
attached to
glycerol by ester
linkages
Archaea
 branched chain
hydrocarbons
attached to
glycerol by ether
linkages
 some have
diglycerol
tetraethers
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Figure 18.4
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Archaeal Taxonomy

two phyla based on Bergey’s Manual
 Euryarchaeota
 Crenarchaeota

16S rRNA and SSU rRNA analysis also
shows
 Group
I are Thaumarchaeota
 Group II are Korachaeota
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Figure 18.1
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


Very high/low temp/pH, concentrated salts or
completely anoxic (extreme environments)
Archae are either gram +ve or gram –ve
Classified into two phylum :
1) Crenarchaeota
2) Euryarchaeota – 5 major physiologic groups
(the metanogens, the halobacteria, the
thermoplasms, extremely thermophilic S°reducers and sulfate-reducing)
Phylum Crenarchaeota

most are extremely thermophilic
 hyperthermophiles
(hydrothermal vents)
most are strict anaerobes
 some are acidophiles
 many are sulfur-dependent

 for
some, used as electron acceptor in
anaerobic respiration
 for some, used as electron source
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Figure 18.9
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Figure 18.10
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Crenarchaeota…
include organotrophs and lithotrophs
(sulfur-oxidizing and hydrogenoxidizing)
 contains 25 genera

 two
best studied are Sulfolobus and
Thermoproteus
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Genus Thermoproteus

long thin rod, bent or branched
 cell

walls composed of glycoprotein
thermoacidophiles
°C
 pH 2.5–6.5
 70–97

anaerobic metabolism
 lithotrophic
on sulfur and hydrogen
 organotrophic on sugars, amino acids, alcohols,
and organic acids using elemental sulfur as
electron acceptor

autotrophic using CO or CO2 as carbon
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Genus Sulfolobus

irregularly lobed, spherical shaped
 cell
walls contain lipoproteins and
carbohydrates

thermoacidophiles
 70–80°C
 pH

2–3
metabolism
 lithotrophic
on sulfur using oxygen (usually)
or ferric iron as electron acceptor
 organotrophic on sugars and amino acids
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Phylum Euryarchaeota
consists of many classes, orders, and
families
 often divided informally into five major
groups

 methanogens
 halobacteria
 thermoplasms
thermophilic S0-metabolizers
 sulfate-reducers
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
The Methanogens
- strict anaerobes
- obtain energy by converting CO2, H2, methanol
to methane or methane & CO2
- eg. Methanobacterium, Methanococcus
- methanogenesis
* last step in the degradation of organic
compounds
*occurs in anaerobic environments
e.g., animal rumens
 e.g., anaerobic sludge digesters
 e.g., within anaerobic protozoa

Ecological and Practical
Importance of Methanogens


important in wastewater treatment
can produce significant amounts of
methane
 can
be used as clean burning fuel and energy
source
 is greenhouse gas and may contribute to
global warming

can oxidize iron
 contributes
pipes
significantly
to corrosion of iron
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
The Halobacteria
- extreme halophiles
- aerobic chemoorganotrophs (use organic
compound as energy sources)
- dependent on high salt content
- cell wall dependent on NaCl, they
disintegrated when [NaCl] < 1.5M
- dead sea
Strategies to Cope with Osmotic
Stress

increase cytoplasmic osmolarity
 use

compatible solutes (small organics)
“salt-in” approach
 use
antiporters and symporters to increase
concentration of KCl and NaCl to level of
external environment

acidic amino acids in proteins
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
The Thermoplasms
- lack cell walls
- but plasma membrane strengthen by diglycerol
tetraether, lipopolysaccharides, and glycoproteins
- grow best at 55-59°C, pH1-2
- eg. Thermoplasma

Extremely Thermophillic So-Reducers
- strictly anaerobic
- can reduce sulfur to sulfide
- grow best at 88-100°C
- motile by flagella
- eg. Thermococcus

Sulfate-reducing
- irregular garm –ve coccoid cells
 cell walls consist of glycoprotein subunits
- extremely thermophilic
 optimum 83°C
 isolated from marine hydrothermal vents
- obtain their energy by oxidizing organic
compounds or H2 while reducing sulfates to
sulfides. In a sense, they "breathe" sulfate rather
than oxygen
- eg. Archaeoglobus
Bacteria
Domain Bacteria

Bacteria are essential to life on Earth.

We should realize that without bacteria, much of
life as we know it would not be possible.

In fact, all organisms made up of eukaryotic
cells probably evolved from bacterialike
organisms, which were some of the earlist forms
of life.
The Proteobacteria





Largest group of bacteria. More than 500 genera
gram-negative, some motile using flagella
Most are facultative/obligate anaerobes
Share common 16s rRNA sequence
5 distinct classes of proteobacteria (α,β, ε, ɣ,δ) :
- Alphaproteobacteria
- Betaproteobacteria
- Gammaproteobacteria
- Deltaproteobacteria
- Epsilonproteobacteria
Figure 20.1
68
Alphaproteobacteria
 Gram -ve
 Most are oligotrophic (capable of growing at low nutrient
levels)
 Example of alphaproteobacteria ;
1) Most purple nonsulfur phototrophs are in this group
(use light energy and CO2 and do not produce O2)
2) Nitrifying bacteria e.g. Nitrobacter (oxidize NH3 to NO3
by a process called nitrification)
3) Pathogenic bacteria eg. Rickettsia (typhus), Brucella
(brucellosis), Ehrlichia (ehlichiosis)
4) Beneficial bacteria eg. Acetobacter and Caulobacter
(synthesize acetic acid); Agrobacterium (used in genetic
recombination in plants)
Purple Nonsulfur Bacteria
with one exception (genus
Rhodocyclus) all are a-proteobacteria
 metabolically flexible

 normally
grow anaerobically as anoxygenic
photoorganoheterotrophs
possess bacteriochlorophylls a or b in
photosystems located in membranes that are
continuous with plasma membrane
 some can oxidize sulfide, but not elemental
sulfur, to sulfate

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Purple Nonsulfur Bacteria…

Rhodospirillum industrial importance
 produces


H2
 novel biodegradable plastic
 oxidize carbon monoxide to carbon dioxide
morphologically diverse
 most motile by polar flagella
found in mud and water of lakes and ponds
with abundant organic matter and low sulfide
levels; some marine species
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Nitrifying Bacteria

very diverse chemolithoautotrophs
 nitrification
– gain electrons from oxidation
of
ammonium to nitrate or nitrite
 nitrite further oxidized to nitrate

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Nitrification
ammonia  nitrite  nitrate
 conversion of ammonia to nitrate by
action of two genera

Nitrosomonas – ammonia to nitrite
 e.g., Nitrobacter – nitrite to nitrate
 e.g.,

fate of nitrate
 easily
used by plants
 lost from soil through leaching or
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Betaproteobacteria
 Gram –ve
 oligotrophic (capable of growing at low nutrient
levels)
 Differ with alphaproteobacteria in rRNA sequence
 Example of betaproteobacteria :
1) nitrifying bacteria eg. Nitrosomonas
2) pathogenic species, Neisseria (gonorrhea),
Bordetella (whooping cough)
3) Thiobacillus (ecologically important), Zoogloea
(sewage treatment)
Gammaproteobacteria – largest class
 purple sulfur bacteria – obligate anaerobes that
oxidize hydrogen sulfide to sulfur
 intracellular pathogens (Legionella, Coxiella),
 methane oxidizers (Methylococcus),
 facultative anaerobes that utilize glycolysis and
the pentose phosphate pathway (Escherichia
coli),
 pseudomonads –aerobes that catabolize
carbohydrates (Pseudomonas, and Azomonas)
Deltaproteobacteria
 Sulfate reducing microbes Eg. Desulfovibrio
(important in the sulfur cycle)
 Myxobacteria – gram negative, soil-dwelling
bacteria , dormant myxospores; common
worldwide in the soils having decaying plant
material or dung
Epsilonproteobacteria
 Gram-negative rods, vibrios, or spiral
 Include important human pathogens
 Eg. Campylobacter (causes blood poisoning)
The Gram Positive Bacteria

In Bergey’s Manual, gram-positive bacteria (able to
form endospore) are divided into those that have :
- low G + C ratio (base pair in genome below 50%)
- high G + C ratio

Low G + C gram-positive bacteria include 3 groups
clostridia, mycoplasms, Gram-positive Bacilli and
Cocci

High G + C gram-positive bacteria include
mycobacteria, corynebacteria, and actinomycetes.
Clostridia
 Eg. Clostridium – anaerobic, form
endospores, rod shape, gram +ve
 pathogenic bacteria causing gangrene,
tetanus, botulism, and diarrhea






Mycoplasmas
Facultative or obligate anaerobes lack cell walls
Gram +ve (previously under gram negative
category until nucleic acid sequences proved
similarity with gram positive organisms)
When culture on agar, form ‘fried egg’
appearance bcoz cell in the center of the colony
grow into the agar while those around the spread
outward
Usually associated with pneumonia and urinary
tract infections
Fried egg appearance




Gram positive Bacilli and Cocci
Eg. Bacillus – form endospores, flagella
(B.licheniformis synthesis antibiotic. B.anthracis
cause anthrax)
Eg. Lactobacillus – nonsporing rods, nonmotile,
produce lactic acid as fermentation product.
Mostly found in human mouth, intestinal tract,
stomach. Protect body from pathogens
Streptococcus – nonmotile, cocci associated in
pairs and chain. Cause pneumonia, scarlet fever
Bacillus
Streptococcus
High G+C gram-positive bacteria




Include Corynebacterium, Mycobacterium and
Actinomycetes that have a G+C ratio > 50% in the phylum
Actinobacteria, which have species with rod-shaped cells
Corynebacterium store phosphates in metachromatic
granules. C. diptheria causes diphtheria
Mycobacterium cause tuberculosis and leporosy. It has
unique resistant cell walls containing mycolic acids.
Hence, acid fast stain (for penetrating waxy cell walls) is
used for its identification
Actinomycetes resemble fungi as they produce spores
and form filaments; important genera: Actinomyces found
in human mouths; Nocardia useful in degradation of
pollutants; and Streptomyces produces antibiotics
THE EUKARYOTES :
FUNGI, ALGAE,
PROTOZOA
FUNGI





Organisms in kingdom fungi include molds,
mushrooms, yeasts
Fungi are aerobic or facultatively anaerobic
(yeast), chemoheterotrophs, spore-bearing,
lack chlorophyll
Most fungi are decomposers, and a few are
parasites of plants and animals
Some fungi – cause disease (mycoses)
Some fungi – essential to many industries
(bread, wine, cheese, soy sauce)
Characteristics of Fungi
Body/vegetative struc. of fungi – Thallus
 Thalli of yeast – small, globular, single cell
 Thalli of mold – large, composed of long,
branched, threadlike filaments of cell called
hyphae that form mycelium
 Hyphae - septate
- Aseptate (coenocytic)
 Fungi grow best in the dark, moist habitats

Acquire nutrients by absorption. Secrete
enzyme to break large organic mol. Into
simple mol.
 Reproduction of fungi – sexual & asexual

Asexual reproduction
Several ways :
1) Transverse fission - Parent cell undergo
mitosis, divide into daughter cell by formation of
new cell wall
2) Budding – after mitosis, one daughter nucleus
is sequestered in a small bleb that is isolated
from parent cell by formation of cell wall
3) Asexual spore formation - filamentous fungi
produce asexual spores through mitosis and
subsequent cell division.
several types of asexual spores :
1) Sporangiospores form inside a sac called
sporangium
2) Chlamydospores form with a thickened cell wall
inside hyphae
3) Conidiospores (conidia) produced at the tip or
side of hyphae, not within sac
4) Blastospores produced from vegetative mother
(hyphae) cell by budding
5) Arthrospores hyphae that fragment into
individual spores
conidiospores
sporangiospores
Chlamydiospores
Arthrospores
conidiospores
chlamydospores
Blastospores
sporangiospores
4) Sexual reproduction in fungi
Fungal mating type designated as + and –.
4 basic steps :
1) Haploid (n) cells from + and – thallus fuse,
form dikaryon (cell with both +&- nuclei)
2) pair of nuclei within a dikaryon fuse to form
one diploid (2n) nucleus
3) meiosis of the diploid restores the haploid
state
4) haploid nuclei partitioned into + and - spores
Classification of fungi
1) Zygomycota
 Coenocytic molds – zygomycetes
 produce sporangiospores (asexual) and
zygospores (sexual)
 e.g. Black bread mold Rhizopus nigricans

usually reproduce asexually by spores that
develop at the tips of aerial hyphae

sexual reproduction occurs when
environmental conditions are not favorable
 requires
compatible opposite mating types
 hormone
production causes hyphae to produce
gametes
 gametes
 zygote
fuse, forming a zygote
becomes zygospore
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Figure 24.4
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96
2) Ascomycota
 Septate hyphae
 Form ascospores within sac-like structure
call asci (sexual)
 Form conidiospores in asexual
reproduction
 Eg Penicillium
Ascomycota

ascomycetes or sac fungi
 found
in freshwater, marine, and terrestrial
habitats
 red, brown, and blue-green molds cause
food spoilage
 some are human and plant pathogens
 some yeasts and truffles are edible
 some used as research tools
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Figure 24.6
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Ascomycota
Yeast Life Cycle

alternates between haploid and diploid
 in
nutrient rich, mitosis and budding occurs
at non-scarred regions

stops after entire mother cell is scarred
 nutrient
poor, meiosis and haploid ascus
containing ascospores formed

haploid cells of opposite mating types fuse

tightly regulated by pheromones
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Figure 24.7
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101
3) Basidiomycota



septate hyphae
produce basidiospores (sexual), some produce
conidiospores (asexual)
Eg mushrooms, puffballs, stinkhorns
Figure 24.12
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Human Impact Basidiomycota
decomposers
 edible and non-edible mushrooms

 toxins

are poisons and hallucinogenic
pathogens of humans, other animals,
and plants
Cryptococcus neoformans –
cryptococcosis
 e.g.,
 systemic
infection, primarily of lungs
and central nervous system
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Protozoa





Eukaryotic, unicellular and lack of cell wall
Motile (cilia, flagella, pseudopodia)
Grow in moist habitats
Some are in group of Planktonic (floating free in
lakes, ocean and form the basis of aquatic food
chain)
Some protozoa can produce a cyst that provides
protection during adverse environmental
conditions


Asexuall reproduction by binary fission,
schizogony/multiple fission
Sexually reproduction by conjugation
1)Nucleus undergoes mitosis
2)Cytoplasm divides by cytokinesis
Schizogony/multiple fission
Classification of protozoa
Grouping based on locomotive structure
do not reflect genetic relationship.
 7 taxa of protozoa : alveolates, cercozoa,
radiolaria, amoebozoa, eglenozoa,
diplomonads, and parabasalids

Alveolates
 Have small membrane cavities called
alveoli beneath cell surface.
 3 groups : ciliates (have cilia),
apicomplexans (pathogen to animal),
dinoflagellates (have flagella)
Cercozoa
 Unicellular, called amoeba
 Move & feed by pseudopodia
 Have snail-like shells of calcium carbonate
Radiolaria
 Amoeba that have ornate shells composed of
silica
Amoebozoa
 Have lobe-shaped pseudopodia, no shell
 Eg Acanthamoeba, Naegleria
Eglenozoa
 move by means of flagella and lack sexual
reproduction; they include Trypanosoma

Diplomonad
 Lack mitocondria, golgi bodie
 Have 2 nuclei and multiple flagella

Giardia
Algae
Simple eukaryotic, phototrophic
organisms, like plants
 Carry out photosynthesis using chlorophyll
 Most live in aquatic environments

Characteristic of Algae
Unicellular or simple multicellular (thalli)
 Thallus of seaweed (large marine algae)
are complex, with holdfast (attached to
rock), stemlike stipes and leaflike blades
 Algae reproduce sexual and asexual
(fragmentation & cell division)

Classification of algae

Classify according to their structure and
pigment :
- red algae
- brown algae – cell wall composed of
cellulosa & alginic acid
- green algae
- diatoms – silica cell wall composed of two
halves called frustules that fit together like
petri dishes
frustule
DIATOMS
VIRUSES
Virus Classification
 classification
based on
numerous characteristics
 nucleic
acid type
 presence or absence of envelop
 capsid symmetry
 dimensions of viron and capsid
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Figure 25.2
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Characteristics of Viruses





Viral disease – SARS, AIDS, influenza, herpes, common
cold
Viruses – miniscule, infectious agent with simple acellular
organization and pattern of reproduction
Viruses can exist – extracellular or intracellular
Virion (complete virus particle) consist of :
- nucleocapsid (composed of 1 or more DNA or RNA, held
within capsid)
- in some viruses – envelope (phospholipid membrane)
Capsid - build by few types of protein = protomer
- 3 types – helical, icosahedral, complex symmetry
Virus structure
Different types of virus
Helical
Icosahedral
Types of capsids
Helical
Complex symmetry




Virus size range 10-1000nm
Most virus infect only particular host’s cells
Eg. HIV only infect T lymphocytes (a type of
white blood cell)
Some viruses infect many kinds of cells in many
different hosts
Eg. Rabies can infect most mammals
Viruses are obligatory intracellular parasites.
They multiply by using the host cell’s
synthesizing machinery to cause the synthesis
of specialized elements that can transfer the
viral nucleic acid to other cells
Viral replication
Virus cannot reproduce themselves bcoz:
- have no genes for all enzyme needed for
replication
- have no ribosomes for protein synthesis
 Viruses dependent of host’s organelles
and enzymes to replicate
 Virus replication – Lytic replication

Lytic replication of bacteriophage

Consist of 5 stages – attachment, entry,
synthesis, assembly, release
1) Attachment – structure responsible for
attachment to host = tail fiber. Attachment is
dependent on chemical attraction and precise fit
between T4 tail and protein receptor on E.coli
cell wall
2) Entry – T4 release lysozyme to weaken
peptidoglycan of E.coli cell wall. T4 inject
genome into E.coli, leaving T4 coat outside.
3-4) Synthesis – viral enzyme degrade the bacterial
DNA. E.coli start synthesis new viruses. T4 DNA
is transcribed, producing mRNA which is
translated to T4 protein (component of tail and
head, lysozyme)
5) Assembly – T4 components are assemble in
spontaneous manner to form mature virion
6) Release – newly assembled virions are released
from the cell as lysozyme completes its work on
the cell wall
Lytic replication takes about 25min can produce
100-200 new virions each cycle