Bacteria.pdf

Bacteria are unicellular, procaryotic microorganisms which have diverse shape size and structures. Bacteria are found almost everywhere on Earth. Even the human body is full of bacteria, and in fact is estimated to contain more bacterial cells than human cells. Most bacteria in the body are harmless, and some are even helpful. A relatively small number of species cause disease.

1. Bacteria
Anup Muni Bajracharya

2. Bacteria
•single-celled microorganisms-Unicellular
•Prokaryoticcells, meaning they lack a membrane-bound
nucleus, do not have a true nucleus, the bacterial nucleus is
known as nucleoid.
•Their genetic material, in the form of a single circular DNA
molecule, is located in the cytoplasm.
•do not have organelles like mitochondria, golgibodies etc
except ribosome.
•Ribosomes present-70Stype
•Bacteria have a cell membrane and a cell wall made of
peptidoglycan, which provides structural support.
•Reproduction occurs throughbinary fission,a process
where a single bacterium divides into two identical
daughter cells.
•Some are motile, due to the presence of flagella

3. Morphology
•Bacteria are diverse microorganisms that exhibit a
wide range of sizes, shapes, and structures.
Size:
•Bacteria are generally much smaller than
eukaryotic cells.
•Most bacteria fall within the range of
➢0.5 to 5 micrometers (µm) in diameter and
➢1 to 10 µm in length.
•However, there are exceptions, such as the giant
bacteria Epulopisciumfishelsoni, which can reach
lengths of up to 0.5 millimeters.

4. Shape
•Morphologically bacteria are divided into
three major shapes:
•Cocci(Singular: coccus)
•Bacilli (rods) (Singular: rod, bacillus)
•Spirilla(Singular: spirillum)

6. Cocci
•from kokkosmeaning berry
•Round or oval bacteria
•measuring about 0.5–1.0 um
in diameter.
•When multiplying, coccimay
form pairs, chains, or
irregular groups:
•cocciin pairs are called
diplococci, e.g. meningococci
and gonococci.
•cocciin chains are called
streptococci,
e.g.Streptococcus pyogenes.
•cocciin irregular groups are
called staphylococci,
e.g.Staphylococcus aureus.
•cocciarangedin square of 4
are called tetrads.
E.g.Micrococcusluteus
•cocciarangedin cubes of 8
are called sarcina.

7. Bacillus
•These are stick-like bacteria with rounded, tapered (fusiform),
square, or swollen ends.
•They measure 1–10 um in length by 0.3–1.0 um in width.
•Different forms of Bacillus
•Bacillus:Single unattached cell, Bacillus cereus, Salmonella enterica
•Diplobacilli:Two rods found in pairs eg-Moraxella bovis, Klebsiella
rhinoscleromatis
•Streptobacilli:bacilli are arranged in a chain. Eg-Streptobacillus
moniliformis, Streptobacillusfelis.
•Coccobacilli:These are short compared to other bacilli and oval in
shape, they appear like a coccus. Eg-Haemophilusinfluenzae,
Gardnerellavaginalis,etc.
•Palisades:The bacilli arranged in a palisade, fence-like structure,
resembling Chinese letters Eg-Corynebacteriumdiptheria

9. Spiral
Spiral bacteria are, as the name suggests, spiral-shaped.
➢Spiral-shaped bacteria occur in one of three forms:
Vibrio,Spirillum, and Spirochete
➢Vibrio-are slightly curved or comma-shapedwith less than one complete turn or twist
in the cell. eg-Vibrio parahaemolyticusandVibrio cholerae.
➢Spirillum(plural, spirilla). A bacterium with rigid spiral (helical) structure, thick, long,
and move with flagella, eg-Campylobacter jejuniandHelicobacter pylori.
➢Spirochete.helical structure and flexible body (not rigid), a thin structure, long.
egTreponemapallidumandLeptospiraborgpetersenii.

10. •Note-Pleomorphic: Some bacteria do not
have a fixed shape and can vary in shape or
undergo changes depending on environmental
conditions.
•These are referred to as pleomorphic bacteria.
Examples include Caulobacterand
Mycoplasma.

11. Bacterial cell Structure and
Function
Anup Muni Bajracharya

12. Structure of bacterial cell
•A. Structure Outside cell wall
•Capsule
•Flagella
•Pili
•Sheath
A typical bacterial cell have following structure.
B. Structure Inside cell wall
Cell wall
Cytoplasmicmembrane
Nucleoid
Mesosome
Ribosome
cytoplasm
Spore

13. Capsule
•viscous layer outside to the cell wall present in
some bacteria.
•Capsule is 98% water and 2% polysaccharide or
glycoprotein/ polypeptide or both.
•There are two types of capsule.
•i.Macro-capsule:thickness of 0.2µm or more,
visible under light microscope
•ii.Microcapsule:thickness less than 0.2µm,
visible under Electron microscope
•Capsule is very delicate structure. It can be
removed by vigorous washing.
•Capsule is most important virulence factor of
bacteria.
•Function:
•It helps in attachments as well as it prevent the
cell from desiccation and drying.
•Capsule resist phagocytosisby WBCs
resist phagocytosis
attachment

14. Capsulesand slime layers
•A glycocalyx, literally meaning "sugar coat"
•is a network ofpolysaccharidesthat project from cellular
surfaces ofbacteria.
•Many bacterial cells secrete -some extracellular material
(glycoclyx) in the form of a capsule or a slime layer.
•A slime layer is loosely associated with the bacterium and
can be easily washed off, whereas a capsule is attached
tightly to the bacterium and has definite boundaries.

15. Flagella
•Flagella (singular, flagellum)-hair like helical structure
emerges from cell wall.
•provide a means of locomotion
•It is 15-20 nm
•composed of flagellinprotein (globular protein) and
known as H antigen.
•Flagella has three parts. Basal body, Hook and filament
•Function:
•It helps in motility of the bacteria
•The flagella beat in a propeller-like motion to help the
bacterium move toward nutrients; away from toxic
chemicals; or, in the case of the photosynthetic
cyanobacteria; towards the light.

16. three parts.
Basal body, Hook and filament

17. Flagellararrangements
Based on their arrangement, bacteria are classified into four
groups:
monotrichous(having one flagellum),
amphitrichous(single flagellum at both ends),
lophotrichous(numerous flagella as a tuft), and
peritrichous(flagella distributed all over the cell except at the
poles)

18. Pilior fimbriae
•Fimbriae and piliarethin, protein tubes originating from
the cytoplasmic membrane of many bacteria.
•Both are able to stick bacteria to surfaces, but piliare
typically longer and fewer in number than fimbriae.
•They are found in virtually all Gram-negative bacteria but
not in many Gram-positive bacteria.
•small hairlikeprojections or hollow filamentous and non-
helical structure.
•They are numerous and shorter than flagella
•Piliis composed of pilinprotein.
•Bacteria containing pili:Shigella, Proteus, Neisseria
gonorrhoae, E. coli

19. Pilior fimbriae
•Function:
•Attachment: pilihelps the bacteria to attach the host cell surface. Most of the
human pathogens of respiratory tract, urinary tract are attached with the help of
pili.
•These outgrowths assist the bacteria in attaching to other cells and surfaces, such
as teeth, intestines, and rocks. Without pili, many disease-causing bacteria lose
their ability to infect because they're unable to attach to host tissue.
•Pili(fimbrae) possess antigenic property
•Specialized function: some piliare modified for specialized function. Eg. Sex pilus
(F-pili) help in transfer of DNA from donor to recipient cell during conjugation.
•F-pilialso act as receptor for bacteriophage.

20. Cell wall
•Each bacterium is enclosed by a rigid cell wall composed of
peptidoglycan, a protein-sugar (polysaccharide) molecule.
•On the basis of cell wall composition, bacteria are classified
into two major group ie.
•Gram Positive and Gram negative.
Gram positive cell wall
Cell wall composition of gram
positive bacteria.
Peptidoglycan
Lipid
Teichoicacid
Gram negative cell wall
Cell wall composition of gram negative
bacteria
Peptidoglycan
Outermembrane:
Lipid
Protein
Lipopopysaccharide(LPS)

24. •Peptidoglycan:
•It consists of glycanbackbone formed by repeated unit of NAG (n-acetyl
Glucosamine) and NAM (N-acetyl muramicacid) and the glycanbackbone
is cross linked by peptide bond.
•Peptidoglycanlayer is present in cell wall of both gram positive as well as
gram negative bacteria. However, gram positive have thick layer of
peptidoglycan.
•Teichoicacid:
•Teichoicacid is water soluble polymer of glycerol or ribitolphosphate
present in gram positive bacteria.
•It constitutes about 50% of dry weight of cell wall.
•It is the major surface antigen of gram positive bacteria
•Outer membrane:
•It is an additional layer present in gram negative bacteria.
•It is composed of lipid bilayer, protein and lipo-polysaccharide(LPS)
•LPS:
•LPS is composed of lipid-A and polysaccharide.
•Lipid-A: it is phosphorylatedglucosamine disaccharide. It is antigenic
•Polysaccharide: it consists of core-polysaccharide and O-polysaccharide.

25. Functions of cell wall
•The wall gives the cell its shape and surrounds
the cytoplasmicmembrane, protecting it from
the environment.
•It also helps to anchor appendages like the pili
and flagella, which originate in the cytoplasm
membrane and protrude through the wall to the
outside.
•The strength of the wall is responsible for keeping the
cell from bursting when there are large differences in
osmotic pressure between the cytoplasm and the
environment.

26. Cell membrane
•Cell membrane is the inner
layer that lies inside the cell
wall and encloses the
cytoplasm.
•It is also known as cytoplasmic
membrane or plasma
membrane.
•It is about 80nm thick.
•Cell membrane of bacteria is
composed of phospholipidand
proteins.
•Function:
•It is selectively permeable as it
allows to pass selective
substances such as sugar,
aminoacidsacross it.

28. Nucleoid
•Bacterial nucleus is known as nucleoid; it lacks nuclear membrane,
nuceloplasmand nucleolus.
•The nucleoidis a region of cytoplasm where the chromosomal DNA
is located. It is not a membrane bound nucleus, but simply an area
of the cytoplasm where the strands of DNA are found.
•Bacterial DNA is naked (lacked histoneprotein)
•Most bacteria have a single, circular chromosome that is
responsible for replication, although a few species do have two or
more.
•Smaller circular auxiliary DNA strands, called plasmids, are also
found in the cytoplasm.
•Function:
•It contains and stores hereditary information of the cell.
•It controls all cell activities.

29. Ribosome
•Ribosomesare rounded granules found freely floating in the
cytoplasm.
•Bacterial ribosome is of 70s type.
•Ribosomesare known as universal cell organelle because it is found
in both bacterial cell and eukaryotic cell.
•Chemically the ribosomesare made up of nucleic acids (particularly
RNA and proteins).
•Function:
•It helps in protein synthesis
•They translate the genetic code from the molecular language of
nucleic acid to that of amino acids—the building blocks of proteins.

30. Mesosome
•Mesosomeis a spherical or round sac like
structure found commonly in gram positive
bacteria.
•Function: It is the site for respiration in
bacterial cell

31. Spores (endospore)
•Spore is metabolically
dormant structure produced
during unfavourable
condition by the process
called sporulation
•Sporulationoccur during late
log phase or early stationary
phase
•Under favourablecondition
spores germinate to give
vegetative cell.