1. The document discusses the discovery and characteristics of bacteria, including their cell structures. Bacteria were first discovered in 1676 by Anton van Leeuwenhoek and later studies by Pasteur and Koch linked them to diseases. 2. Bacteria have diverse morphologies and sizes but generally lack organelles. Their cells contain genetic material, ribosomes, and may have a cell wall, capsule, flagella or fimbriae. Cell walls differ between gram-positive and gram-negative bacteria. 3. Important groups discussed include Archaea, Eubacteria, Mycoplasma (wall-less bacteria) and L-forms (wall-less derivative bacteria). Characteristics, structures and differences between

1. MICROBIOLOGY
Welcome to
Bacteria Discovery, general characteristics; Types-
archaebacteria, eubacteria, wall-less forms (mycoplasma
and spheroplasts); Cell structure of eubacteria
By
N. Sannigrahi, Associate Professor,
Department of Botany,
Nistarini College, Purulia (W.B.) India

2. DISCOVERY OF BACTERIA
 The beauty of the diversity of the living organisms is treasure of
biologists and the awesome diversity of microorganisms a pleasure
for solitude to all the human beings. Bacteria are microscopic
organisms, which are often known as ‘germs’ and ‘microbes’. They
are among the simplest forms of life known, and, hence show the
characteristics of both plants and animals. Their relationship to other
living organism is very obscure. Though they are placed in the plant
kingdom, this does not mean that they are more closely related to
plants than to animals. Their inclusion under the plant kingdom is
entirely for the sake of convenience.
 Since the discovery of bacteria in 1676 by Anton van Leeuwenhoek,
a Dutchman, they were objects of curiosity until middle of the
nineteenth century, when Louis Pasteur and Robert Koch
demonstrated that these organisms are responsible for some of the
most important diseases of human beings and animals.

3. PROKARIOTIC BACTERIA

4. DISCOVERY OF BACTERIA
 Their brilliant work revolutionized medicine and pioneered the
field of antiseptic surgery paving the way for the development
of the study of bacteria into independent science of
bacteriology. It was Pasteur who disproved the theory of
spontaneous generation by furnishing irrefutable evidence that
microorganisms arise from pre-existing living entities.
 He also demonstrated that fermentation is a biological
phenomenon rather than a purely chemical one.
 Koch’s experimental methods made possible the formulation
of rules or postulates, which are followed whenever possible,
before a suspected organism could be finally accepted as the
cause of a specific disease. These are known as Koch’s
Postulates or Rules of proof.

5. KOCH’S POSTULATES
 1. The organism must be consistently associated with the
disease in question.
 2. The organism must be isolated from the diseased plant or
animal and grown in pure culture and accurately described.
 3. The organism of the pure culture, when inoculated back into
healthy plant or animal, must be capable of reproducing the
characteristic symptoms of the disease.
 The organism must be re-isolated from the diseased plant or
animal tissue, grown in pure culture and must be identical with
the original inoculated organism.
 All these postulates have been accepted as working guides by
workers of diseases of human beings and other animals, and
also of plants. But they are not applicable in case of viruses,
insects, and fungi which cannot be grown on artificial media.

6. ARCHAEBACTERIA
 Archaea’ is a domain in the biological world of living
organisms and includes the prokaryotic, unicellular bacteria
having specific composition and metabolism different from the
true ( Eubacteria) bacterial domain. The term was first coined
by Woese and Fox( 1977) in his system of phylogeny. The tem
was later replaced by Woese, Kandler and Wheelis (1990)
giving a new domain name ‘ Achaea”. The Achaean cells have
been dated to almost 3.5 billion years ago found to restricted
in the extreme and harsh habitats. Different morphological
features like needle (Thermofilum), rectangular (
Thermoprotem) or irregular rods (Sulfobolus) withg cell ranges
from 0.1 micrometer to 15 µm in diameter. Sometimes
multicellular colonial aggregation take place. Most of the
features of the Achaean are almost identical to bacterial cells
but the key features are as below:

7. ARCHAEBACTERIA CHARACTERS
 The cell membrane contains glycerol either lipids in contrast
to glycerol-ester lipids .The ether bonds are stress resistant and
the enzymes are different from the others.
 The cell wall is made up of proteins but does not contain
peptidoglycan. Distinct 5 types of cell wall like Type 1, 2, 3–
etc are found.
 The Achaean flagellum is very unique motile, thinner than
bacterial flagella with preproteins.Archaea flagellum are
bundle of many filaments that rotate as a single unit.
 Genome is like prokaryotes having single circular DNA as its
chromosome. The genes are located throughout the genome
with repetitive DNA sequences In most of the cases, G+C
content is higher , can be up to 68%.
 Reproduce asexually by binary fission, fragmentation or
budding, no spore or no sexual acts like conjugation,
transformation etc.

8. DIFFERENCE : EUBACTERIA & ARCHAEA
Characters Eubacteria Archaea
Habitat Present everywhere In extreme harsh
condition
Cell wall With peptidoglycan,
Muramic acid
No peptidoglycan or
Muramic acid
Cell membrane Ester linked, straight
chain of fatty acids
present with L-glycerol
phosphates
Ether linked with
branched aliphatic chains
RNA polymerase Simple, subunit pattern,
one kind
Complex, subunit pattern
similar like eukaryotes
Introns Absent or very rare Present in some species
Spore formation Occurs, Endospore
formation takes place
No spore formation
Flagella Thicker, has internal
hollow channels
Thinner, solid

9. MYCOPLASMA
 Mycoplasma , a unique group of prokaryotic organisms
without cell wall , pathogenic to human beings, plants and
cattle was first discovered by Raux( 1898) in connection with
pleuronpenumonia in cattles.The most widely studied species
Mycoplasma mycoides var. mycoides causing bovine
pleuropneumonia disease. It shapes a number of characters:
 Extremely minute organisms , polymorphic without any
definite shape,
 Lack cell wall and the plasma membrane is triple layered and
competent enough to protect them having polysaccharides in
addition to normal structure.
 Steroid required for growth, Cells are delicate, motile and can
be compared with L form of bacteria, Contain both RNA &
DNA, Genome size small with prokaryotic ribosome, resistant
to most antibiotics

10. MYCOPLASMA

11. MYCOPLASMA
 Mycoplasma exhibit 4 types of structures-
 Elementary bodies- small, electron dense, spherical to ovoid,
surrounded by unit membrane with ribosome in the cytoplasm,
 Large cells- mature spherical cells uniform in dimension (410-
590mm), each is surrounded by unit membrane , ribosome free
or polysomes, a nuclear zone without distinct nucleus,
 Very large cells- degenerated non viable cells with smaller
number of vesicles,
 Filamentous structure- Uniform width (60-75 nm) with triple
layered cell membrane, all 3 RNAs found.
 Reproduction takes place by budding, binary fission or intra
cellular production of elementary bodies.

12. WALLLESS BACTERIA
 Bacteria without cell wall-wall less bacteria or L-form bacteria
cell wall deficient (CFD) bacteria, first isolated by Emmay K
Nobel (1935).
 Two types- Unstable L-forms & Sphaeroplast which are stable
L-forms can revert to original morphology.
 Mycoplasma are wall less but not as L-forms as they are not
derived from normal bacteria without cell wall,
 Wall less have no definite shapes , either rounded or spherical,
 They are indifferent to gram staining,
 Mostly budding in which the extensions of thin protrusions
from the cell surface takes place which are then pinched off to
form new cells,
 Novel elements for recombinant protein expression in
biotechnology research.

13. EUBACTERIA:GENERAL CHARACTERISTICS
 True bacteria or Eubacteria are characterized by the following
features: Unicellular in nature but grouping of cell can be
observed,
 Do not have distinct nucleus but nucleoid like structure called
genophore present without the components of nucleus,
 Possess cell wall outer to the cell membrane but a slime
capsule layer external to cell wall in some cases,
 The cell wall contains N-acetyl muramic acid(NAMA) and N-
acetyl glucosamine( NAGA) which is absent in Achaea. It
contains diamino pimelic acid,
 The genetic material id ds DNA that acts as genome, No
histone is present in genophore
 Do not possess any membrane bound organelles like
chloroplastids, mitochondria along with Golgi bodies
.However,.

14. GENERAL CHARACTERISTICS
 The inward folding of the inner cell membrane forms
mesosomes acts as respiratory organelle,
 Ribosome is 70S which are free or in polysomes for protein
synthesis,
 Most bacteria have an absorptive mode of nutrition, the
autotrophic and chemosynthetic group possess the capacity to
synthesize food,
 No nuclesome formation found in bacteria,
 Reproduce by binary fission; No sexual reproduction but some
bacteria have sexual like mode of reproduction by conjugation,
transformation and transduction,
 Plasmids or extra circular genome is present in some bacteria,
 Some bacteria possess motility due to flagella on their sell
surface which is made up of 8 parallel chains of flagellin
protein.

15. MORPHOLOGY
 The size, shape and the arrangement of the bacterial cell vary
with shapes in which it belong to . They are within 1-5 µ and
the smallest bacterium is 0.15 µ to 0.3 µ; the largest bacterium
is Bacillus butschilli is about 3.0 µ to 6.0 µ in width and 80 µ
in length. Cell size of some common bacteria is given below:
 Clostridium botulinum (Food poisoning)- 3.8 µ
 C. tetani ( Tetanus)-2-5 µ,
 Corynebacterium diphtheriae ( Diphtheria)-1-8 µ,
 Mycobacterium tuberculosis ( Tuberculosis)- 0.5-4 µ
 Neisseria meningitidis ( Meningitis) – 1 µ
 Staphylococcus sp ( Boils) 0.8 µ
 Treponema pallidum (Syphilis) 6-14 µ

16. MORPHOLOGY
 The shape of the bacteria depends upon the arrangement of the
cells .Basically, they are of following types-bacillus, coccous,
spirilum, vibrio and comma. But each of them have diverse
morphology:
 Coccus- may be diplococcus,( Cell divide on one plane)
Streptococcus( divide in one plane and remain attached to
form a linear chain of cells), Tetracocci ( divide in two planes
and form four groups of cells), Straphylococci ( divide in three
planes and form irregular pattern) and Sarcinae ( divide in
three planes and producing branches of cocci).
 Bacillus- Monobacillus, Diplobacillus, Streptobacillus,
Coccobacillus etc.
 Spirilli- Vibrioid , Helical etc.
 Hyphae- Multicellular, thin walled, profusely branched
filamentous

17. STRUCTURE OF BACTERIAL CELL
 As far as the structural aspects of the bacterial cell is
concerned, it enjoys a wide diversity but the basic pattern of
the cell structure is as follows with some modifications in the
particular component.
 The covering comprising of capsule, slime layer and cell wall,
 Surface appendages- External outgrowths to perform diverse
functions
 Cell wall-Protective covering against harsh environment,
shape of the cell to ensure stability
 The cell membrane- the exchange of substances to & fro
 The cytoplasm- the contents nourish ribosome and other
constituents
 The genome- the genetic material to regulation of cell
 The Plasmid- the extra chromosomal body beside DNA

18. CAPSULE & SLIME LAYER
 The capsule or slime layer is known as glycocalyx popularly
known as ‘sugar coat, most outer covering made up of
polysaccharide,
 When the layer is distinct and persistent gelatinous mass,
difficult to remove called capsule,
 When this outer layer is loose, irregular diffused layer, can be
deformed and removed called slime layer,
 Capsule is a rigid covering with high molecular weight of
glucose, amino sugars, muramic acid, rhmnose , poly D-
Glutamic acid etc,
 Capsule shows immunological specificity,
 The external coating is extremely hydrated
 Defensive mechanisms, acts as reserve food matters and
makes it virulent to bacteria with least desiccation.

19. BACTERIA WITH CAPSULE

20. SURFACE LAYER-S
 In addition to glycocalyx, some bacteria and archaebacteria an
additional surface layer ( S-layer) inner to capsule,
 All S-layers are composed of two dimensional array of
proteins and crystalline appearance,
 In Gram (+) bacteria, it is associated with peptidoglycan of the
cell wall and in Gram (-) bacteria, it is associated with outer
membrane,
 It acts as permeability barrier for large substances, helps in
within the host by conferring protection against host defense
mechanisms and protects from ion and pH fluctuations.
◦ Thus, the different external coverings of the bacteria play a
very important role of the survival of this microscopic entity
even in the most harsh environmental fluctuations.

21. SURFACE APPENDAGES
 The surface appendages are of three types- Flagella, Fimbriae
or Spinae
 FLAGELLA: It protrudes from the cell wall responsible for
motility as well as fertility, a whip like filament(20 nm in
diameter), a motor complex and a hook that connects the two,
Filament comprising of protofilament with flagellin sub units
and the protoifilaments are held together by cap.
 On the basis of distribution, it may be
 Atrichous- without flagella,
 Monotrichous- Having single flagellum,
 Lophotrichous- A tuft of flagella at the one end,
 Amphitrichous- each end having one flagellum,
 Peritrichous- Multiple flagella at different locations
 Cephalotrichous-Two or more flagella is attached at one end .

22. BACTERIA & FLAGELLA

23. FIMBRAE, PILLI & SPINAE
 Short, fine hair like structure in bacteria,
 Non-locomotive structures , thin observed under electron
microscope,
 Pilli made up of protein called pilin,
 Fimbrae help in attaching in substrate, help in forming
biofilms, helps in genetic material transfer and in some cases
in gliding motion,
 One or two sex pilli are found and their presence is genetically
determined,
 Pilli helps in formation of conjugation bridge,
 Spinae are rigid hairy appendages in some Gram (-) bacteria
made up of spinin helps in bacteria to adapt in harsh
environmental conditions

24. CELL WALL
 Present inner to capsule or slime layer and very close to cell
membrane,
 Made up of peptidoglycans-polymers of NAG & NAM along
with short chains of amino acids,
 NAG & NAM are arranged alternately to each other by β 1-4
bonds to form a carbohydrate back bone or the glycan,
 Rows of NAG & NAM are linked by a polypeptides in cross
bridge manner,
 The structural integrity of cell depends on the cross linking of
basic structural repeating units,
 While peptidoglycan present, two basic variations seen in
bacteria- Gram(+) and Gram (-) on the basis of differential
staining. Other compounds like teichoic acid, teicharonic acid ,
porin and some lipoproteins are found.

25. BACTERIAL CELL WALL

26. DIFFERENCE
Gram (+) Gram (-)
Very thick, homogenous Thin and tri-layered
90% of the cell wall consists of
peptidoglycan
NAG & NAM are tightly close
together to give more rigid structure
Peptidoglycam consists of 10% of the
total content. NAG & NAM are
loosely joined together
Contains lysine but DAP is not found No lysine but DAP present
Teichoic acid and other
polysaccharides, proteins present
No Teichoic acid but phospholipids,
proteins and lipopolysaccharides are
present
Teichoic acids are main surface
antigen
Lipopolysaccharides act as surface
antigen
More sensitive to wall attacking
antibiotics
Less sensitive to antibiotics

27. PLASMA MEMBRANE
 Inner to cell wall and outer boundary of protoplasm,
 Cell wall can be removed by enzymatic actions and it is called
protoplast, sometimes a portion of cell wall remains attached
to protoplast called spheroplast,
 The plasma membrane is triple layered structure with
bimolecular lipid middle layer sandwiched by two layers of
proteins on either side,
 It contains 60% proteins, 30% lipids and 10% carbohydrates.
Sterols are absent,
 Certain intra cellular membrane structures continuous cell
membrane are formed called mesosomes and are common in
Gram(+) bacteria than Gram(-) bacteria,
 It helps in maintaining osmotic pressure of the cell, transport
nutrients, helps in energy generation and septum formation
during cell division.

28. CYTOPLASM
 Entire thing is the protoplasm called matrix or cell pool,
 It contains number of substances in aqueous medium like
lipoproteins, nucleoproteins, amino acids, vitamins, glucose,
ribose and so many inclusions like granules, PHB, glycogens,
gas vacuoles, carboxysomes, RNAs, DNA etc,
 Ribosome is typical 70S type with 2 subunits-50S & 30S. A
ribosome is 250-350 A in diameter, number varies from 5000-
10000 either free or polysome condition. The 50S subunit
contains 2 moles of rRNA with sedimentation coefficient of 5S
and 23S with 30-40 structural proteins. The 30S subunit
contains 1 rRNA with 16S coefficient and 24 structural
proteins.
 The Ribosome are involved in protein synthesis and it is the
repository of 85% of the total RNA of the bacterial cell.

29. BACTERIAL GENOME
 Have circular dsDNA molecule that forms the visible mass
called nucleoid not bounded by membrane,
 The bacterial length of DNA is 1000 times more than the
length of cell itself and oriented highly organized within cell,
 The nucleoid contains 60% DNA, 30% RNA and 10% protein
by weight,
 The bacterial chromosome is without histone and does not
have introns,
 Kavanoff and Ryder (1976) suggested a rosette appearance of
the nucleoid where the central core is held together by RNA-
DNA interactions and nearly 12-80 topologically independent
loops or domains of super coiling radiate from this zone,
 Contains only single copy of the gene , there is no allele,
referred as haploid.

30. PLASMIDS
 Plasmids are extra or additional DNA molecules in the
bacterial cell other than the bacterial nucleoid, discovered by
Lederberg ( 1952),
 Self replicating circular DNA molecule carrying few but
essential genes in the cytoplasm in addition to the main
genome, One molecule of plasmid having size from 1kbp to
400 kbp,
 Plasmids can be easily removed from the cell and manipulated
for which they form the main tool of the recombinant DNA
technology, In conjugation process, plasmid can be transferred
from one bacterial cell to other,
 Plasmid of three types- Conjugative, non-conjugative and
intermediate ,On the basis of functions , plasmids are –F (
fertility), R (Resistance), col plasmid, degradative plasmid,

31. PLASMIDS

32. PLASMIDS
 virulence plasmid or addition plasmid, Ti plasmid, Ri
plasmids.
 These types of plasmids transfer the respective factor to other
bacterial cell during conjugation,
 Some plasmids can integrate with the bacterial genome and
they are called episome .All episomes are plasmids but all
plasmids are not episomes,
 The number of plasmid is generally 1 per cell but in some
cases it may be more than one . The number of plasmid in a
bacteria cell is referred as the copy number. A plasmids
contains 5-100 genes that determine the biological function
and provide special features to bacterial cell for survivability.
 Thus this small circular self replicating and dsDNA helps the
bacteria fir multiple identity and now being used in recDNA
technology for human welfare.

33. PLASMID FOR GENETIC ENGINEERING

34. THANKS FOR YOUR JOURNEY
 REFERENCES:
 Different websites
 Google for images
 Brock Biology of Microorganisms
 A textbook of Microbiology by Dubey & Maheaswari,
 Microbiology & Phycology- Mishra & Dash
 A textbook of Microbiology- Pelzer, Chan & Krieg,
 The presenter acknowledges all the owners to use the different images
used in this presentation This has been prepared for the stakeholders
without any financial interest and to be used as open source of learning.