Bacteria Lecture

Course: Bacteria

E Learning Module for
BSc Ist Year Students

Course Developed by
Dr. Anita Singh
Assistant Professor

Botany Department
CMP Degree College, Prayagraj

Bacteria

Evolution/Classification

Prokaryotes
The oldest fossils known, nearly 3.5 billion years old,
are fossils of bacteria-like organisms.

Evolution has yielded many species adapted to survive
where no other organisms can.

Grouped based on:

Structure, physiology, molecular Composition, reaction
to specific types of stain (Gram Positive/Gram Negative).
• Eubacteria= Germs/bacteria
• Archaebacteria

Kingdom Archaebacteria

 First discovered in extreme environments
 Methanogens: Harvest energy by converting H2 and

CO2 into methane gas
Anaerobic, live in intestinal tracts

 Extreme halophiles: Salt loving, live in Great Salt
Lake, and Dead sea.

 Thermoacidophiles: Live in acid environments and
high temps.
Hot Springs, volcanic vents

 Depending on the
species,

 bacteria can be
aerobic which
means they require
oxygen to live

 or

anaerobic which • Green patches are green sulfur
means oxygen is bacteria.
deadly to them.
• The rust patches are colonies of
purple non sulfur bacteria.

• The red patches are purple sulfur
bacteria

Chemosynthetic bacteria use the sulfur
in the “smoke” for energy to make ATP.

The red color of this snow is due to a blue-green bacteria

Kingdom Eubacteria

 Can have one of three basic shapes
1.Bacilli – rod-shaped
2.Spirilla – spiral-shaped
3.Cocci – sphere-shaped

 Can live in colonies
Strepto – in chains
Staphylo – grape-like clusters
Diplo – pairs

Structure of Bacteria
Size of Bacteria

 Average bacteria 0.5 - 2.0 mm in diam.
RBC is 7.5 um in diam.

 Surface Area ~12 mm
 Volume is ~4 mm
 Surface Area to Volume is 3:1

 Typical Eukaryote Cell SA/Vol is 0.3:1

 Food enters through SA, quickly reaches all parts of bacteria

 Eukaryotes need structures & organelles

Shapes of Bacteria

 Coccus
Chain = Streptococcus
Cluster = Staphylococcus

 Bacillus
Chain = Streptobacillus

 Coccobacillus
 Vibrio = curved
 Spirillum
 Spirochete
 Square
 Star









Bacterial Structures

 Flagella
 Pili
 Capsule
 Plasma Membrane
 Cytoplasm
 Cell Wall
 Lipopolysaccharides
 Teichoic Acids
 Inclusions
 Spores

Flagella

 Motility – movement
 Swarming occurs with some bacteria

Spread across Petri Dish
Proteus species most evident
 Arrangement basis for classification
Monotrichous; 1 flagella
Lophotrichous; tuft at one end
Amphitrichous; both ends
Peritrichous; all around bacteria
 Observe Picture in Micro Lab.

Chapter 4

Mono- or Lophotrichorus



Pili

 Short protein appendages
 smaller than flagella

 Adhere bacteria to surfaces
 E. coli has numerous types
K88, K99, F41, etc.
 Antibodies to will block adherence

 F-pilus; used in conjugation
 Exchange of genetic information

 Flotation; increase buoyancy
 Pellicle (scum on water)
 More oxygen on surface

F-Pilus for Conjugation

Capsule or Slime Layer

 Glycocalyx - Polysaccharide on external
surface

 Adhere bacteria to surface
 Prevents Phagocytosis

Cytoplasm

 80% Water {20% Salts-Proteins)
 Osmotic Shock important

 DNA is circular, Haploid
 Advantages of 1N DNA over 2N DNA
 More efficient; grows quicker
 Mutations allow adaptation to environment quicker

 Plasmids; extra circular DNA
 Antibiotic Resistance

 No organelles (Mitochondria, Golgi, etc.)

Cell Membrane

 Bilayer Phospholipid
 Water can penetrate
 Flexible
 Not strong, ruptures easily

Osmotic Pressure created by cytoplasm







Cell Wall

 Peptido-glycan Polymer (amino acids +
sugars)

 Unique to bacteria
 Sugars; NAG & NAM

N-acetylglucosamine
N-acetymuramic acid
 D form of Amino acids used not L form
Hard to break down D form
 Amino acids cross link NAG & NAM



Cell wall comparison of Gram +ve and Gram –ve Bacteria



Detailed Cell wall structure of Bacteria

Characteristic features of Gram-positive
cell wall

1. Thick peptidoglycan layer.

2. Teichoic acids and lipoteichoic acids are present,
which serve to act as chelating agents, and also for
certain types of adherence.

3. Capsule polysaccharides.

4. Thick and featureless.

5. No lipid and often no protein.

Characteristic features of Gram-negative
cell wall

1. Thin peptidoglycan layer (which is present in much higher levels in gram-
positive bacteria).

2. Outer membrane containing lipopolysaccharide outside the peptidoglycan
layer.

3. Porins exist in the outer membrane, which act like pores for particular
molecules.

4. There is a space between the layers of peptidoglycan and the secondary
cell membrane called the periplasmic space.

5. No teichoic acids or lipoteichoic acids are present.

6. Lipoproteins are attached to the polysaccharide backbone whereas in
gram-positive bacteria no lipoproteins are present.

Endospores

 Resistant structure
 Heat, irradiation, cold
 Boiling >1 hr still viable

 Takes time and energy to make spores
 Location important in classification

 Central, Subterminal, Terminal
 Bacillus stearothermophilus -spores

 Used for quality control of heat sterilization equipment
 Bacillus anthracis - spores

 Used in biological warfare



Metabolism of Bacteria

Autotrophic -The cellular carbon is obtained by fixing carbon dioxide.

e.g., green sulfur bacteria, phototrophic cyanobacteria. These forms can
make their own food in the presence of sunlight. Sulfur oxidizing bacteria
also belong to this type.

Heterotrophic -Organic carbon compounds are used as carbon
source. e.g., E. coli, Bacillus, Clostridium, etc. They require at least
one organic nutrient such as glucose to make other organic
compounds.

On the basis of requirement of oxygen:

Obligate aerobes: oxygen is required for metabolism. It is also the terminal electron
acceptor. For e.g., Nitrobacter.

Obligate anaerobes: Which do not use molecular oxygen as terminal electron acceptor. It
is toxic to these organisms. E.g., Clostridium. In such organisms, nitrate,
sulfate or organic compounds are the electron acceptor.

facultative anaerobes :Some micro-organisms can also grow either in the presence or
absence of molecular oxygen. These organisms are called. E.g., E. coli.

Microaerophillic: Besides above types there are organisms that grow at reduced oxygen
concentrations but are obligate aerobes. They are called E.g., Campylobacter,
Azospirillum.

On the basis of energy

• Phototrophy is the use of light through
photosynthesis. Photosynthesis is a process of
manufacture of food from carbon dioxide and
water in the presence of sunlight and
chlorophyll.

• Chemotrophy is the use of chemical
substances for energy. These are mostly
oxidized by the use of oxygen or alternative
electron acceptors (aerobic/anaerobic
respiration).

Nitrogen Fixation

Nitrogen fixing bacteria present in the soil take
part in this process.
Nitrogen fixing bacteria and other microorganisms that fix
nitrogen are called diazotrophs.
These organisms have a nitrogen fixing enzyme system based on
iron-molybdenum nitrogenase.
Ex. Rhizobia sp.

Rhizobia

Rhizobia are bacteria found in soil which
develop a symbiotic relationship with legumes.

Nitrogen fixation takes place in nodules of legumes.

The tissue of nodules in which nitrogen fixation occurs has a
molecule leghaemoglobin

This molecule reduces the amount of free oxygen as well as
protects the nitrogen fixing enzyme nitrogenase.

Chapter 4

Chapter 4

The Nitrogen Cycle

Chapter 4

Bacterial Reproduction

Bacteria reproduce using two basic methods: asexual reproduction
and sexual reproduction.

1. Asexual Reproduction

Binary Fission-1. Bacterial cell; 2-3: Duplication of the genetic material; 4-5: Septum
formation and distinct wall formation; 6: Separation of cells.

2. Sexual Reproduction

1. Conjugation

Bacterial conjugation involves several
steps:

First the physical contact between the
cells is made by the Pilli.

One strand of plasmid is transferred
from the donor (F+)to the recipient (F-).

The recipient synthesizes a
complementary strand to become F+
cell and the donor synthesizes a
complementary strand restoring its
complete plasmid.

Chapter 4

2. Transduction

Transduction is of two types:
1. Generalized and 2.Specialized.

A. Generalized

Step 1. Phage infects bacteria

Step 2. The host DNA is hydrolysed into pieces and phage
DNA and proteins are synthesized

Step 3. Sometimes a bacterial DNA is packaged into phage
capsid

Step 4. The phage infects new bacteria and recombination
may occur
Step 5. Resulting bacteria has entirely new genotype.

B. Specialized Transduction

Step 1. Bacterial cell has a prophage integrated between
the genes A and B,

Step 2. The prophage may exit incorrectly taking some of
the host DNA along with it.

Step 3. The viral DNA has the bacterial gene A integrated
in it.

Step 4. The phage infects new bacteria and recombination
may occur

Step 5. Resulting bacteria has entirely new genotype.

3. Transformation

Economic Importance:
Bacteria in Technology and Industry

Mining
Acidothiobacillus ferrooxidans is the important organism in the mining process. The presence of these bacteria speeds up the process and miners
can extract metal even from low-grade ores in a cost effective manner.
Antibiotics

Vitamins
Vitamin B12 is produced by many bacteria. eg. Pseudomonas denitrificans. Deficiency of Vitamin B12 causes
pernicious anaemia.
Bioremediation
Bio remediation uses living organisms to eliminate environmental hazards that result
from accumulation of toxic chemicals or wastes. Ex. Pseudomonas sp.

Bacteria in Technology and Industry

Fermentation
Bacteria, often Lactobacillus in combination with yeasts and molds, have been used to prepare fermented
foods such as cheese, pickles, soy sauce, sauerkraut, vinegar, wine and yoghurt.

Probiotic
Probiotic means ‘for life’. They are living microbes which when given in proper amount give health benefits
to the hosts. They are present in soya beverages, yogurt, etc.

Biological Pest Control
Bacteria can also be used in place of pesticides in the biological pest control. This commonly involves
Bacillus thuringiensis (also called BT), a Gram-positive, soil dwelling bacterium.

Genetic Tools
Because of their ability to quickly grow and the relative ease with which they can be manipulated, bacteria are
the workhorses for the fields of molecular biology, genetics and biochemistry.