Transcript Bacterial Classification, Anatomy, Nutrition, Growth, Metabolism and

Bacterial Classification,
Anatomy, Nutrition,
Growth, Metabolism and
Genetics
Classification Systems in the Prokaryotes
1.
2.
3.
4.
5.
6.
Macroscopic morphology
•
Colony appearance & color
•
Texture & size
Microscopic morphology
•
Cell shape, size
•
Staining
Physiological / biochemical characteristics
•
Enzymes
Chemical analysis
•
Chemical compound of cell wall
Serological analysis
1.
Ag/ Ab binding
Genetic and molecular analysis
•
G + C base composition
•
Nucleic acid sequencing and rRNA analysis
G + C base composition

Low G+C Gram-Positive Bacteria
 Clostridia
 Mycoplasmas

High G+C Gram-Positive Bacteria
 Corynebacterium
 Mycobacterium
Bacterial Taxonomy Based on
Bergey’s Manual

Bergey’s Manual of Determinative
Bacteriology – five volume resource
covering all known procaryotes
based on genetic information –
phylogenetic
 two domains: Archaea and Bacteria
 five major subgroups with 25 different phyla
 classification
Major Taxonomic Groups of Bacteria



Vol 1A: Domain Archaea
 primitive, adapted to extreme habitats and modes of
nutrition
Vol 1B: Domain Bacteria
Vol 2-5:
 2 - Phylum Proteobacteria – Gram-negative cell
walls
 3 - Phylum Firmicutes – mainly Gram-positive with
low G + C content
 4 - Phylum Actinobacteria – Gram-positive with high
G + C content
 5 – Loose assemblage of phyla – All gram negative
Species and Subspecies

Species
 bacterial
cells which share overall similar pattern of
traits

Subspecies
 Strain
or variety
 culture derived from a single parent that differs in
structure or metabolism from other cultures of that
species
 E. coli O157:H7

Type
 subspecies
that can show differences
Bacterial Shapes, Arrangements, and Sizes

Typically described by one of
three basic shapes:
 coccus

Spherical
 bacillus

Rod


coccobacillus
vibrio
 spirillum

Helical, twisted rod,

Spirochete
Bacterial Shapes, Arrangements, and Sizes

Arrangement of cells dependent on pattern of
division and how cells remain attached after
division:
 cocci:
 singles
 diplococci
 tetrads
 chains
 irregular clusters
 cubical packets
 bacilli:
 chains
 palisades
Cocci
Bacilli
Bacterial anatomy
Generalized structure of a prokaryotic cell
Appendages: Cell Extensions Flagella

3 parts
 filament
 long, thin, helical structure
composed of proteins
 Hook
 curved sheath
 basal body
 stack of rings firmly anchored
in cell wall
 rotates 360o

1-2 or many distributed
over entire cell
Flagellar Arrangements

monotrichous

single flagellum at one
end
lophotrichous


small bunches arising
from one end of cell
amphitrichous


flagella at both ends
of cell
peritrichous


flagella dispersed over
surface of cell, slowest
Fig. 4.4
Movement by flagella

Polar




Rotates counterclockwise
Cell swims forward in
runs
Reverse will stop it
Peritrichous

All flagella sweep
towards one end
Chemotaxis
Internal Flagella  Axial Filaments


aka Periplasmic
Endoflagella


Spirochetes
enclosed between cell
wall and cell membrane
of spirochetes
Appendages for Attachment  Fimbrae
fine hairlike bristles
from the cell surface
 function in adhesion
to other cells and
surfaces

Appendages for Mating Pili




rigid tubular structure
made of pilin protein
found only in Gram
negative cells
Functions



joins bacterial cells for DNA
transfer (conjugation)
Adhesion
to form biofilms and
microcolonies
The Cell Envelope


External covering outside the cytoplasm
Composed of few basic layers:

glycocalyx
 cell wall
 cell membrane

Maintains cell integrity
The Cell Membrane



fluid layer of phospholipid and protein
phospholipid molecules are arranged in a bilayer
Hydrophobic fatty acid chains in the phospholipids form a
permeability barrier
The Bacterial Surface Coating
Glycocalyx



Coating of molecules
external to the cell wall
Made of sugars and/or
proteins
functions



attachment
inhibits killing by white
blood cells
receptor
The Bacterial Surface Coating
Glycocalyx

2 types:
1. slime layer loosely organized
and attached
2. capsule - highly
organized, tightly
attached
Cell Wall

Four Groups Based on Cell Wall
Composition:
1. Gram
positive cells
2. Gram negative cells
3. Bacteria without cell walls
4. Bacteria with chemically unique cell walls
Structure of the Cell Wall Peptidoglycan

macromolecule
composed of a
repeating framework
of long glycan chains
 cross-linked
by short
peptide fragments

provides strong,
flexible support
 keep
bacteria from
bursting or collapsing
because of changes
in osmotic pressure
Gram Positive Cell Wall (1)

Consists of

a thick, homogenous
sheath of peptidoglycan




tightly bound acidic
polysaccharides
teichoic acid and
lipoteichoic acid
Periplasmic space
cell membrane
Gram Negative Cell Wall (2)

Consists of






an outer membrane
containing
lipopolysaccharide (LPS)
periplasmic space
thin shell of peptidoglycan
periplasmic space
cell membrane
Protective structure while
providing some flexibility
and sensitivity to lysis
Gram Negative Cell Wall

LPS



endotoxin that may
become toxic when
released during infections
may function as receptors
and blocking immune
response
contains porin proteins in
upper layer

Regulates molecules
entering and leaving cell
The Gram Stain



Important basis of bacterial
classification and identification
Practical aid in diagnosing infection
and guiding drug treatment
Differential stain

Gram-negative


lose crystal violet and stain red from
safranin counterstain
Gram-positive

retain crystal violet and stain purple
Atypical Cell Walls

Some bacterial groups lack typical cell wall
structure
 Mycobacterium and Nocardia
 Gram-positive cell wall structure with lipid mycolic
 pathogenicity
 high degree of resistance to certain chemicals and dyes
 basis for acid-fast stain

Some have no cell wall
 Mycoplasma
 cell wall is stabilized
 pleomorphic
by sterols
acid
Chromosome



single, circular, doublestranded DNA molecule
contains all the genetic
information required by a
cell
DNA is tightly coiled
around a protein


dense area called the
nucleoid
central subcompartment in
the cytoplasm where DNA
aggregates
Plasmids



small circular, doublestranded DNA
stable extrachromosomal
DNA elements that carry
nonessential genetic
information
duplicated and passed on to
offspring

replicate independently from the
chromosome
Plasmids


may encode antibiotic
resistance, tolerance to toxic
metals, enzymes & toxins
used in genetic engineering



readily manipulated &
transferred from cell to cell
F plasmids allow genetic
material to be transferred from
a donor cell to a recipient
R plasmids carry genes for
resistance to antibiotics
Storage Bodies Inclusions & Granules



intracellular storage
bodies
vary in size, number &
content
Examples:




Glycogen
poly-b-hydroxybutyrate
gas vesicles for floating
sulfur
Endospores


resting, dormant cells
produced by some G+ genera




Clostridium, Bacillus & Sporosarcina
resistance linked to high levels of
calcium & certain acids
longevity verges on immortality
 25 to 250 million years
pressurized steam at 120oC for
20-30 minutes will destroy
Endospores

have a 2-phase life cycle



sporulation


formation of endospores
Germination


vegetative cell
endospore
return to vegetative growth
withstand extremes in heat,
drying, freezing, radiation &
chemicals
Endospores
• stressed cell
• undergoes asymmetrical cell division
• creating small prespore and larger
mother cell
• prespore contains:



•
mother cell matures the prespore
into an endospore
•
•
Cytoplasm
DNA
dipicolinic acid
then disintegrates
environmental conditions are again
favorable
protective layers break down
• spore germinates into a vegetative
cell
•
Microbial nutrition,
growth, and
metabolism
Obtaining Carbon

Heterotroph
 organism
that obtains carbon in an organic
form made by other living organisms
 proteins, carbohydrates, lipids and nucleic
acids

Autotroph

an organism that uses CO2 (an inorganic
gas) as its carbon source
 not dependent on other living things
Growth Factors

organic compounds
that cannot be
synthesized by an
organism & must be
provided as a nutrient


essential amino acids,
vitamins
Carbon Energy
source source
photoautotrophs
CO2
sunlight
chemoautotrophs
CO2
Simple
inorganic
chemicals
photoheterotrophs
organic
sunlight
Nutritional types

Chemo

Chemical compounds
Photo
light
chemoheterotrophs organic
Metabolizing
organic cmpds
Types of Heterotrophs


Saprobes
Parasites / pathogens
 Obligate
Nutritional Movement
Osmosis
 Facilitated diffusion
 Active transport
 Endocytosis

 Phagocytosis
 Pinocytosis
Extracellular
Digestion


digestion of complex
nutrient material into
simple, absorbable
nutrients
accomplished through
the secretion of
enzymes (exoenzymes)
into the extracellular
environment
Environmental Influences on
Microbial Growth
1.
 2.
 3.
 4.
 5.
 6.

temperature
oxygen requirements
pH
Osmotic pressure
UV light
Barophiles
1. Temperatures

Minimum temperature
 lowest
temperature that
permits a microbe’s growth
and metabolism

Maximum temperature
 highest
temperature that
permits a microbe’s growth
and metabolism

Optimum temperature
 promotes
the fastest rate of
growth and metabolism
Temperature Adaptation Groups
Psychrophiles

optimum temperature 15oC
capable of growth at 0 - 20oC
•
•
Mesophiles

optimum temperature 40oC
Range 10o - 40oC (45)
most human pathogens
•
•
•
Thermophiles

optimum temperature 60oC
capable of growth at 40 - 70oC
•
•

Hyperthermophiles


Archaea that grow optimally
above 80°C
found in seafloor hot-water
vents
2. Oxygen Requirements

Aerobe


requires oxygen
Obligate aerobe
 cannot
grow without
oxygen

Anaerobe
 does


not require oxygen
Obligate anaerobe
Facultative anaerobe and aerobe
 capable
of growth in the absence OR
presence of oxygen

Fluid thioglycollate media can be used to
test an organism’s oxygen sensitivity
 Gas chamber
3. pH

The pH Scale
 Ranges
from 0 - 14
 pH below 7 is acidic

 pH

 pH

[H+] > [OH-]
above 7 is alkaline
[OH-] > [H+]
of 7 is neutral
[H+] = [OH-]
3. pH

Acidophiles


Neutrophiles


optimum pH is relatively to
highly acidic
optimum pH ranges about
pH 7 (plus or minus)
Alkaphiles

optimum pH is relatively to
highly basic
4. Osmotic Pressure

Bacteria 80% water
 Require

water to grow
Sufficiently hypertonic media at concentrations
greater than those inside the cell cause water
loss from the cell
 Osmosis
 Fluid leaves the bacteria causing the
 Causes the cell membrane to separate

Plasmolysis
 Cell

cell to contract
shrinkage
extreme or obligate halophiles
 Adapted
to and require high salt concentrations
5. UV Light


Great for killing bacteria
Damages the DNA
(making little breaks)



in sufficient quantity can kill
the organisms
in a lower range causes
mutagenisis
Endospores tend to be
resistant

can survive much longer
exposures
6. Barophiles

Bacteria that grow at
moderately high hydrostatic
pressures



Barotolerants


Grows at pressures from 100500 Atm
Barophilic


Oceans
membranes and enzymes
depend on pressure to
maintain their threedimensional, functional shape
400-500
Extreme barophilic

Higher than 500
Microbial Associations

Symbiotic
 organisms

live in close nutritional relationships;
Mutualism
Obligatory
 Dependent
 Both members benefit


Commensalism
One member benefits
 Other member not harmed


Parasitism
Parasite is dependent and benefits
 Host is harmed

Microbial Associations

Non-symbiotic
 organisms
are free-living
 relationships not required for survival

Synergism


members cooperate and share nutrients
Antagonism

some member are inhibited or destroyed by others
Microbial Associations

Biofilms


Complex relationships
among numerous
microorganisms
Develop an extracellular
matrix




Adheres cells to one
another
Allows attachment to a
substrate
Sequesters nutrients
May protect individuals in
the biofilm
Microbial Growth in Bacteria

Binary fission:
 Prokaryotes
reproduce
asexually
 one cell becomes two

basis for population growth
 Process:



parent cell enlarges
duplicates its chromosome
forms a central septum

divides the cell into two
daughter cells
Population Growth


Generation / doubling time
 time required for a complete
fission cycle
 Length of the generation time
is a measure of the growth rate
of an organism
Some populations can grow from
a small number of cells to several
million in only a few hours!!
Prokaryotic Growth

Bacterial Growth Curve
•
lag phase
•
•
logarithmic (log) phase
•
•
•
Exponential growth of the population occurs
Human disease symptoms usually develop
stationary phase
•
•
no cell division occurs while bacteria adapt to their new
environment
When reproductive and death rates equalize
decline (exponential death) phase
•
accumulation of waste products and scarcity of resources
Other Methods of Analyzing
Population Growth
Turbidity
 Direct microscopic count
 Coulter counting

Turbidity
Direct Microscopic Count
Electronic Counting
Microbial genetics
Genomes
Prokaryotic Genomes

Prokaryotic
chromosomes



Main portion of DNA, along
with associated proteins
and RNA
Prokaryotic cells are
haploid (single
chromosome copy)
Typical chromosome is
circular molecule of DNA in
nucleoid
DNA Replication in Prokaryotes
Genetic Recombination in Prokaryotes
 Genetic recombination
 occurs when an organism acquires
and expresses genes that
originated in another organism

Genetic information in prokaryotes
can be transferred vertically and
horizontally

Vertical gene transfer (VGT)


transfer of genetic material from
parent cell to daughter cell
Horizontal gene transfer (HGT)


transfer of DNA from a donor cell to
a recipient cell
Three types



Bacterial conjugation
Transformation
Transduction
DNA Recombination Events

3 means for exogenous genetic
recombination in bacteria:
Conjugation
2. Transformation
3. Transduction
1.
Transmission of Exogenous
Genetic Material in Bacteria
conjugation
requires the attachment of two
related species & formation of a
bridge that can transport DNA
transformation
transfer of naked DNA
transduction
DNA transfer mediated by
bacterial virus
1. Conjugation

transfer of a plasmid or chromosomal fragment from
a donor cell to a recipient cell via direct connection

Gram-negative
 cell donor has a fertility plasmid
 (F plasmid, F′ factor)
 allows the synthesis of a conjugation (sex) pilus
 recipient
cell is a related species or genus
without a fertility plasmid
 donor transfers fertility plasmid to recipient
through pilus
 F+ and F-
Physical Conjugation
2. Transformation

chromosome fragments from a
lysed cell are accepted by a
recipient cell
 genetic
code of DNA fragment is
acquired by recipient


Donor and recipient cells can be
unrelated
Useful tool in recombinant DNA
technology
Transformation of Insulin Gene







human insulin gene isolated and cut from its
location on the human chromosome
 using a restriction enzyme
plasmid is cut using the same restriction
enzyme
desired DNA (insulin gene) and plasmid DNA
can be joined using DNA ligase
plasmid now contains the genetic instructions
on how to produce the protein insulin
Bacteria can be artificially induced to take up
the recombinant DNA plasmids and be
transformed
 successfully transformed bacteria will
contain the desired insulin gene
transformed bacteria containing the insulin
gene can be isolated and grown
As transformed bacteria grow they will produce
the insulin proteins coded for the recombinant
DNA
 Insulin harvested and used to treat
diabetes
3. Transduction


DNA is transferred from one
bacterium to another by a
virus
Bacteriophages
 Virus
that infects bacteria
 consist of an outer protein
capsid enclosing genetic
material
 serves as a carrier of DNA
from a donor cell to a recipient
cell
Other ways genetics can change:
Transposons
 Mutations

Transposons


Special DNA segments that have the
capability of moving from one location
in the genome to another
 “jumping genes”
Can move from

one chromosome site to anotherr
 chromosome to a plasmid
 plasmid to a chromosome

May be beneficial or harmful
 Changes in traits
 Replacement of damaged DNA
 Transfer of drug resistance
Mutations

Result of natural
processes or induced
 Spontaneous


mutations
heritable changes to the
base sequence in DNA
result from natural
phenomena such as
radiation or uncorrected
errors in replication
 UV
light is a physical
mutagen that creates a
dimer that cannot be
transcribed properly

Nitrous acid is a chemical mutagen that converts
adenine bases to hypoxanthine
 Hypoxanthine

base pairs with cytosine instead of thymine
Base analogs bear a close resemblance to
nitrogenous bases and can cause replication errors
Point Mutation



Result of spontaneous or
induced mutations
affects just one base pair
in a gene
Base-pair substitutions


result in an incorrect base in
transcribed mRNA codons
Base-pair deletion or
insertion

results in an incorrect
number of bases
Repair Mechanisms


Attempt to correct mistakes or damage in the DNA
Mismatch repair involves DNA polymerase


“proofreading” the new strand
removing mismatched nucleotides

Excision repair
 involves
cutting out
damaged DNA
 replacing it with
correct nucleotides