This document provides an overview of bacteria, including their general characteristics, morphology, ultrastructure, and distribution. It discusses that bacteria are unicellular microorganisms that exist as single cells and have a very high surface area to volume ratio. Their cell structure includes a cell membrane, cell wall, mesosomes, ribosomes, and may also have a capsule, flagella, or fimbriae. Bacteria come in a variety of shapes (cocci, bacilli, spirilla) and sizes ranging from 0.2 to 500 micrometers. They are found widely in all environments including water, soil, plants, animals, and human bodies.

1. THE BACTERIA
General Characters & a Closure Look
V. W. PATIL
Institute of Science, Aurangabad – Maharashtra
(India)
[AW – Student ID: 49fdafcae9b911e9a8b43f9b844f09b7]

2. Acknowledgement
 The presenter is thankful to the ‘Course Coordinator’ and
‘Team Members’ of a MOOC ‘ACADEMIC WRITING’ on
SWAYAM platform for the designing and developing a course
meticulously.
 The idea behind the development of such online MOOCs by
UGC which are free to its users is admired by the presenter.
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3. Bacteria – General Characters
 Defn (Oxford) of Biology (Gk, bios = life, logos = to discourse/ to
study):
 It is the study of living organisms, and is divided into many
specialized fields that cover their morphology, physiology, anatomy,
behaviour, origin, and distribution.
 Bacteriology is a branch of microbiology dealing with the
identification, study, and cultivation of bacteria and with their
applications in medicine, agriculture, industry, and biotechnology.
 The term bacteria (Pl.) [Sing., Bacterium] include large number of
unicellular microorganisms distributed in air, water, soil, bodies of
living plants and animals, as well as in the dead organic matter too.
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4. Bacteria – General Characters
 Microbe is French term which means microscopic organism or
organisms especially pathogenic.
 Germ is any microorganism which is pathogenic or disease
producing bacteria.
 The terms, microbe & germ are synonymous to bacterium.
 Bacteria are very minute organisms. Unlike plants &animals, they do
not exit as parts of organisms. But, they exist as single cells.
 Since their smaller size, they have very high surface-to-volume ratio
which is approximately 2,00,000 times greater than a similar ratio for
an adult human being.
 They have very high metabolic rates and their multiplication occurs
every after 20 min.
 R. H. Whittaker (1969) divided the living world into five kingdoms:
Monera, Protista, Plantae, Fungi and Animalia.CC BY-SA-NC4

5. Whittaker’s Kingdom – Monera
 1. It includes all prokaryotic cells,
 2. Lack nuclear membrane, plastids, mitochondria & advanced
(9+2 strand) flagella,
 3. Solitary, unicellular or colonial unicellular organization,
 4. Nutrition is of absorptive type, but some groups are
photosynthetic or chemosynthetic,
 5. Reproduction – asexual by fission or budding, however,
protosexual phenomena also occur,
 6. Motile by simple flagella, motility by gliding or non-motile.
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6. Whittaker’s Kingdom – Monera
 Branch 1: Myxomonera include the forms without flagella, motility (if
present) by gliding movement.
 o Phylum: Cyanophyta – Blue-green algae
 o Phylum: Myxobacteriae – Gliding bacteria
 Branch 2: Mastigomonera include motile forms with simple flagella
(and related non-motile forms).
 o Phylum: Eubacteriae – True bacteria
 o Phylum: Actinomycota – Mycelial bacteria
 o Phylum: Spirochaetae – Spirochaetes (flexible in forms)
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7. Distribution of Bacteria
 Bacteria are widely distributed everywhere in nature:
 They are very common in ponds & ditches, running streams & rivers,
seawater, soil, air, foods, petroleum oil, rubbish & manure heaps,
decaying organic matter, body surface & cavities, as well as in
intestinal tracts of animals.
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8. Functions of Bacteria
 1. They attack human & animal carcasses and mineralize the
organic constituents.
 2. Some forms an association with plant roots & helps in
atmospheric N2 fixation.
 Sulphur & phosphorus are converted to soluble inorganic salts.
 3. They are necessary for sewage disposal.
 4. Souring of milk for butter preparation.
 5. Various industrial fermentations are carried out by the action of
bacteria on carbohydrates.
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9. Morphology of Bacteria
 Shapes of Bacteria:
 The bacteria possess three fundamental shapes – Spherical, Rod
and Spiral or Curved rod.
 Almost all bacteria show ‘pleomorphism’ in more or less degree.
But, still they maintain their definite cell form in controlled conditions.
 A) Spherical Bacteria (Coccus /Cocci)
 These organisms bear apparently perfect spheres or slightly
elongated or ellipsoidal in shape.
 B) Rod-shaped (Bacilli /Bacillus)
 These bacteria appear as cylinders (sometimes ellipsoidal in
shape) with ends more or less rounded or flat or in between
these two extremities.
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10. Morphology of Bacteria
 C) Spiral or Curved rod (Spirilla / Vibrios)
 Curved and spiral-shaped bacteria have a common
microscopic morphology representing curved, helical, or spiral-
shaped rods.
 Shape and size of bacteria is governed by the presence of cell wall.
 But, sometimes various environmental factors such as: (a)
temperature of incubation, (b) age of culture, (c) concentration of
substrate, and (d) the composition of medium, may also results in
variations.
 Bacteria show the characteristic morphology in young cultures
and the media possessing favourable conditions for growth.
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11. Size of Bacteria
 The bacteria show a great variation in their size.
 Some are so small and are beyond the approach of light
microscope.
 e.g. Pelagibacter ubique; with length 0.37 – 0.89µm and 0.12 –
0.20µm in diameter.
 Some are so large and are almost visible to the naked eyes.
 e.g. Thiomargarita namibiensis; 100 – 200 µm, sometimes
750µm
 But, none can be seen without the aid of a microscope.
 In spherical forms, size is measured in terms of a diameter;
whereas, in rod-shaped forms, the length & breadth are
measured for their sizes.
 In case of spiral forms, the apparent length & breadth are
considered.
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12. Size of Bacteria
http://cdn.yourarticlelibrary.com/wp-
content/uploads/2014/03/clip_image002_thumb61.jpg
Fig: Various shapes of
bacteria
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13. Units of length used in bacteriology
 The bacterial size is measured in micrometers, µm (= microns,
µ).
 1µ = 10-6m = 10-4cm = 10-3 mm
 Bacteria generally ranges from 0.2µm or less (Mycoplasma) to
500µm (Spirochaeta).
 These can be measured by ocular micrometer or through
softwares available in market.
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14. The Bacterial Cell – A Closure Look (Ultrastructure)
 A bacterial cell consists of:
 Compound membrane enclosing protoplasm (jelly-like, colourless,
transparent OR a thick, viscous semi-fluid with high percentage of
water),
 Fine granules,
 Vacuoles,
 Mesosomes,
 Ribosomes,
 Polysaccharides,
 Lipids,
 Plasmids (extra-chromosomal DNA), etc.
 Externally, bacteria cell may also show the presence of capsule(s),
fimbriae (pili), and/or flagella.
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15. The Bacterial Cell – A Closure Look (Ultrastructure)
 Cell Membranes:
 This complex structure includes: (i) an inner cytoplasmic
membrane, (ii) cell wall, and (iii) an outer slime layer or
capsule.
 Cytoplasmic Membrane
 It appears in young cells as an ‘interfacial fluid film’ but
becomes ‘thicker & denser’ in later development.
 Composition:
 It contributes almost 10% to the total dry weight of the cell.
 It is composed of approx. 75% of proteins, 20 – 30 % lipids,
and 2% of carbohydrates.
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16. The Bacterial Cell – A Closure Look (Ultrastructure)
 Composition:
 It takes deep stain with basic/ neutral dyes with wide range of
pH.
 It is semipermeable in nature.
 The concentration of protoplasm (metabolites) inside may
reach to 20atm (=osmotic pressure) or approx. 300 lb PSI. The
cell can withstand this pressure due to the rigid cell wall
outside).
 The cytoplasmic membrane of many bacteria possesses
intracellular membranous system, called mesosomes.
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17. The Bacterial Cell – A Closure Look (Ultrastructure)
 Mesosomes or Chondrioids:
 These structures are the invaginations of the cytoplasmic
membrane.
 They are most conspicuous in gram +ve bacteria, and may
appear in two different forms.
 a) Vesicular type: e.g. Bacillus subtilis
 b) Lamellar type: The lamellae results from the coiling up
of the membranes. e.g. Lactobacillus plantarum
 The exact functions of these mesosomes is unknown (clearly
not understood yet) but, may get involved in linking cytoplasmic
membrane and the nucleus as those with ER.
Lamellar type
Vesicular
type
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18. The Bacterial Cell – A Closure Look (Ultrastructure)
 Cell wall:
 It is a rigid structure; selectively permeable and has low
affinity for stains.
 Still it stains lightly with basic fuchsin and methyl violets; but,
can be stained deeply with a mordant such as tannic acid.
 The treatment with this mordant increases the ‘thickness of
the cell’.
 The cell wall accounts for 20% of dry weight of a cell and forms
a major structural component of the cell. It ranges from 10-23
nm.
 Cell Wall Composition:
 In higher plants, it is composed of cellulose (polymer of
glucose); whereas, in molds it is made up of chitin (polymer of
acetylated glucosamine). CC BY-SA-NC18

19. The Bacterial Cell – A Closure Look (Ultrastructure)
 Cell Wall in gram +ve Bacteria:
 It is 20 – 80 nm in thickness and
also includes a transparent
layer – cytoplasmic membrane
measuring 7.5nm in thickness.
 Cell wall is composed of
peptidoglycans, also called
mucopeptide, glycopeptides,
or murein.
 Peptidoglycans are composed
of N-acetylglucosamine, N-
acetylmuramic acid, L-alanine,
D-alanine, D-glutamic acid,
meso-diaminopimelic acid, or L-
lysine.
https://3.bp.blogspot.com/-
HYVXMtRb9q0/WxrBv1wHVxI/AAAAAAAAKYU/Nv6
adZOhISMabqRvCpzDvjDkMQLKEBFEgCLcBGAs/s
1600/gram%2Bpositive%2Bvs%2Bgram%2Bnegativ
e%2Bbacteria.png
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20. The Bacterial Cell – A Closure Look (Ultrastructure)
 Cell Wall in gram -ve Bacteria:
 It is complex in
organization/composition, but is
thinner than the gram +ve bacteria.
 A rigid peptidoglycan layer (2-3nm
in thickness) is located between the
inner cytoplasmic membrane and
an outer multiple-track layer which
is made up of lipoproteins and
lipopolysaccharide complexes.
 The external multiple-track layers, a
rigid peptidoglycan layer and a
cytoplasmic membrane together
constitute a ‘bacterial envelope’.
https://3.bp.blogspot.com/-
HYVXMtRb9q0/WxrBv1wHVxI/AAAAAAAAKYU/Nv6ad
ZOhISMabqRvCpzDvjDkMQLKEBFEgCLcBGAs/s160
0/gram%2Bpositive%2Bvs%2Bgram%2Bnegative%2B
bacteria.png
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21. The Bacterial Cell – A Closure Look (Ultrastructure)
 Slime Layer and Capsule:
 These are extracellular,
slimy or gelatinous
polysaccharide-like
material produced by
bacteria showing
mucoid growth.
 It may remain firmly
attached to the cell
forming ‘capsule’ or
may part freely from the
cell as a free slime or
gum.
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22. The Bacterial Cell – A Closure Look (Ultrastructure)
 Flagella:
 It is a hair-like organ especially for the motility of
an organism.
 It is a long, slender and delicate organ and can
be easily detached from the cell.
 They show wide variations in different species:
 a) Monotrichous – If a single flagella is
present at one end
 b) Amphitrichous – If the flagella are
present one at each end
 c) Lophotrichous – When a tuft of
flagellae are present at one or both
the ends
 d) Peritrichous – When the flagellae are
present all over the surface
Monotrichous
Lophotrichou
s
Lophotrichou
s
Peritrichous
Amphitrichou
s
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23. The Bacterial Cell – A Closure Look (Ultrastructure)
 Flagella:
 A flagellum possesses three different parts:
 (i) Basal body – It anchors the flagellum to the cell
envelope
 (ii) Hook region – connects shaft to the basal body (it is
proteinaceous)
 (iii) Filament or Shaft – It is longer than the cell itself (made
up of flagellin)
 Flagella are not the only means of motility in the organisms, but
some can move by ‘gliding motion’.
A flagella structure in Gram –ve bacteria
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24. The Bacterial Cell – A Closure Look (Ultrastructure)
 Fimbriae (Pl) [Sing – Fimbria]:
 These are the ‘surface appendages’
and are straight, hair-like &
proteinaceous in nature.
 They are the characteristic mainly of
Gram –ve bacteria.
 They remain distributed on all over the
surface or may occur in tuft at the
particular site.
 They play an important role by
enabling bacteria: (a) to stick to
surfaces, (b) to stick with other
plants/animals cells, and (c) to stick
with other bacterial cells.
Cell-surface appendages of
a bacterial cell
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25. The Bacterial Cell – A Closure Look (Ultrastructure)
 Pili (Pl) [Sing – Pilus]:
 These are hair-like, proteinaceous
surface outgrowths which occur on
some Gram –ve cells.
 They have a role in ‘conjugation’, i.e.
passing genetic material to another
cell.
 They are sometimes called ‘sex pili’
and confusingly ‘sex fimbriae’.
Cell-surface appendages of
a bacterial cell
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26. References
 Salle, A.J., Fundamental Principles of Bacteriology (7th Edition-
Reprint, 2008), TMH Publications, New Delhi.
 http://www.biologydiscussion.com/essay/essay-on-bacteria-
biology/21706
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27. Feedback to the Course – Academic Writing
 The course is very beneficial to the students and blooming
researchers to begin and shape their ideas at the first step of
their career.
 This course is focused mainly to fill the gap in knowledge
needed for effective and result oriented academic writing.
 The course attracts towards its most important module of
‘PLAGIARISM’ which is a real challenge to maintain the AW
standards in recent publications.
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