MORPHOLOGY OF BACTERIA DR.RUPAL PATEL. Kingdom : PROTISTA Prokaryotes :evolutionarily ancient. first...

MORPHOLOGY OF BACTERIADR.RUPAL PATEL

Kingdom : PROTISTA Prokaryotes :evolutionarily ancient. first and for billions

of years ,only form of life.. Pro = “before”, karyon = “nucleus” Prokaryotes :

Prokaryotes most always single-celled,. Lack a membrane bound nucleus. Genetic material naked within the cytoplasm, Ribosomes their only type of organelle. Nucleoid region of cytoplasm where chromosomal DNA is

located, usually a singular, circular chromosome. Reproduce by means of binary fission, duplicating their

genetic material and then essentially splitting to form two daughter cells identical to the parent.

Bacteria (including the blue green "algae") are prokaryotes.

Higher organisms together with microorganisms such as fungi, protozoa are eukaryotes.

PROKARYOTES VERSUS EUKARYOTES

PROKARYOTES EUKARYOTES

a) Size 1-10 microns 10-100 microns

b) Complexity unicellular, rarely small clusters or filaments

sometimes unicellular more often multicellular

c) Membrane bound organelles

none (mesosome is infolding of cytoplasmic membrane)

nuclei, mitochondria, chloroplasts, lysosomes, endoplasmic reticulum, golgi, & vacuoles

d) Nucleus no yes

e) Chromosomes single & circular usually several & linear

f) Mitosis & Meiosis absent present

g) Endocytosis & cytoplasmic streaming

absent present

h)Sterols usually absent used as hormones and in plasma membrane

SHAPES OF BACTERIA

Coccus Chain =

Streptoccus Cluster =

Staphylococcus Bacillus

Chain = Streptobacillus

Coccobacillus Vibrio = curved Spirillum Spirochete

COCCUS:

The cocci are spherical or oval bacteria having one of several distinct arrangements:

BACILLUS:

Bacilli are rod-shaped bacteria. They divide in one plane producing one of the following:

SPIRAL:

A helical or corkscrew-shaped bacterium. Spirals come in 1 of 3 form

Vibrio: curved or comma-shaped rod

Spirillum: thick, rigid spiral Spirochete: thin, flexible

spiral

BACTERIAL STRUCTURES

Cell Wall - Lipopolysaccharides

-Teichoic Acids Plasma Membrane Cytoplasm Flagella Pili (fimbria) Capsule Inclusions Spores

CELL WALL 20-40% of bacteria Unique structure which surrounds the cell membrane. Not present in every bacterial species Functions : -Maintaining the cell's characteristic shape

-Countering the effects of osmotic pressure

-Providing attachment sites for bacteriophages- teichoic acids attached to the outer surface of the wall are like landing pads for viruses that infect bacteria

-Providing a rigid platform for surface appendages- flagella, fimbriae, and pili

Some antibiotics effect directly Penicillin

CELL WALL Peptido-glycan Polymer (amino acids

+ sugars) Sugars; NAG & NAM

- N-acetylglucosamine - N-acetymuramic acid

D form of Amino acids used The peptidoglycan polymer is composed of an

alternating sequence of N-acetylglucosamine and N-acetyl-muraminic acid.

Each peptidoglycan layer is connected, or cross linked, to the other by a bridge made of amino acids and amino acid derivatives.

The cross linked peptidoglycan molecules form a network which covers the cell like a grid.

The cell walls of all bacteria are not identical. Cell wall composition is one of the most

important factors in bacterial species analysis and differentiation.

There are two major types of walls: -Gram-positive and Gram-

negative.

Gram-positive bacteria

Many polymer layers of peptidoglycan connected by amino acid bridges.

90% of the Gram-positive cell wall is comprised of peptidoglycan.

TEICHOIC ACIDS -Glycerol, Phosphates, & Ribitol

-Attachment for Phages

Gram-negative bacteria Much thinner, only 20% peptidoglycan. Two unique regions

A) Periplasmic space - separates the outer plasma membrane from the

peptidoglycan layer. - contains proteins which destroy potentially dangerous

foreign matter present in this space.

B) Lipopolysaccharide layer(LPS) - Located adjacent to the exterior peptidoglycan layer. - Phospholipid bilayer attached to the peptidoglycan by

lipoproteins. -The lipid portion of the LPS contains a toxic substance,

called Lipid A, responsible for most of the pathogenic affects associated with harmful Gram-negative bacteria.

-Polysaccharides extend out from the bilayer contibute to the toxicity of LPS.

The LPS, lipoproteins, and the associated polysaccharides together form what is known as the outer membrane

LPS (CONT’D)

Functions Toxic:

Gm -ve septicemia; death due to LPS Pyrogen; causes fever

Heat Resistant; hard to remove Acetone or alcohol can remove O Antigen of Salmonella and E. coli

2,000 different O Ags of Salmonella 100’s different O Ags of E. coli

E. coli O157

CYTOPLASMIC MEMBRANE :DELICATE AND PLASTIC STRUCTURE THAT COMPLETELY ENCLOSES THE CELL CYTOPLASM (OR PROTOPLASM)

Made up of a phospholipid bilayer

Proteins are embedded in the membrane.

-TRANSPORT proteins that BIND specific molecules and carry them into or out of the cell as required.

These proteins are held in the membrane by virtue of hydrophobic and hydrophilic regions on the protein.

Contains enzymes involved in cellular respiration, peptidoglycan biosynthesis

CYTOPLASM Colloidal system containing organic and

inorganic solutes in a viscous watery solution

Ribosomes : -protein synthesis

-slightly smaller than eukaryotic cells (70 S) Mesosomes : -vesicular, convoluted or multilaminated structures

- site of the synthesis of cross wall septa Intracytoplasmic inclusions - volutin granules present in Diptheria bacilli

NUCLEUS

No nuclear membrane

Genome :single , circular ,double stranded DNA

Extra nuclear genetic elements : Plasmids - transferred from one bacterium to another either

through conjugation or through bacteriophages

- confer properties like toxigenecity and drug resistance

FLAGELLA

Flagella are whip-like structures protruding from the bacterial cell wall and are responsible for bacterial motility (i.e. movement).

Long (3 to 12 µm), diameter about 12-30 nanometers The protein subunits of a flagellum are assembled to

form a cylindrical structure with a hollow core. Immunogenic Constitute a group of protein antigens called the H

antigens, which are characteristic of a given species, strain, or variant of an organism.

Antigenic changes of the flagella known as the phase variation of H1 and H2 occurs in Salmonella typhimurium

A flagellum consists of three parts: (1) long filament, which lies external to the cell surface; (2) hook structure at the end of the filament; (3) basal body, to which the hook is anchored with series of rings that drive the flagella. and which imparts motion to the flagellum.

Typical arrangements of bacterial flagella

DETECTING BACTERIAL MOTILITY

1. Flagellar stains : outline flagella and show their pattern of distribution. If a bacterium possesses flagella, it is presumed to be motile.

2.Motility test medium :. -Semisolid medium (0.5 % - 0.75% agar ) inoculated with bacteria in a straight- line stab. -After incubation : turbidity (cloudiness) due to bacterial growth away from the line of the stab : bacteria able to swim through the medium.

3. Direct microscopic observation in a wet mount. -Brownian movement, due to random collisions between water molecules and bacterial cells. -True motility ,bacterium swim from one side of the microscope field to the other side.

FIMBRIAE AND PILI Fimbria :

-protein tubes that extend out from the outer membrane.

-generally short in length

-present in high numbers about the entire bacterial cell surface.

-facilitate the attachment of a bacterium to a surface (e.g. to form a biofilm) or to other cells (e.g. animal cells during pathogenesis).

Pili :

-similar in structure

-much longer

-present on the bacterial cell in low numbers.

-involved in the process of bacterial conjugation.

Fimbriae (common pili) and flagella on the surface of bacterial cells. Left: dividing Shigella enclosed in fimbriae. The structures are probably involved in the bacterium's ability to adhere to the intestinal surface. Right: dividing pair of Salmonella displaying both its peritrichous flagella and its fimbriae. The fimbriae are much shorter and slightly smaller in diameter than flagella.

CAPSULES AND SLIME LAYERS

A true capsule : Discrete detectable layer of polysaccharides deposited outside the cell wall. Sharply defined.

Slime layer (biofilm ):A less discrete structure or matrix which embeds the cells .Loose undemarked secretion

Glycocalyx or microcapsule: very thin layer of tangled polysaccharide fibers on the cell surface.

Generally composed of polysaccharides; rarely they contain amino sugars or peptides.

FUNCTIONS Adherence of cells to surfaces.

Protect bacterial cells from engulfment by protozoa or white blood cells (phagocytes)

Protect from attack by antimicrobial agents

protect cells from effects of drying or desiccation.

Ability to block some step in the phagocytic process so prevent the bacterial cells from being engulfed or destroyed by phagocytes (white blood cells).

-Streptococcus pneumoniae (lobar pneumonia)

-Bacillus anthracis (anthrax)

-Neisseria meningitidis (meningitis

SPORE Endospores are highly heat-resistant, dehydrated resting

cells formed intracellularly in members of the genera Bacillus and Clostridium.

Sporulation, the process of forming endospores, is an unusual property of certain bacteria.

The process, usually begins in the stationary phase of the

vegetative cell cycle, is initiated by depletion of nutrients (usually readily utilizable sources of carbon or nitrogen, or both).

The cell then undergoes a highly complex, well-defined sequence of morphologic and biochemical events that ultimately lead to the formation of mature endospores.

Structure of a bacterial endospore, renowned as the most durable and long-lived type of cell on earth

The cross section of a bacterial spore, such as anthrax, shows its hard, multilayered coats, which both make the spore difficult to kill and allow it to remain dormant for many years.

At the beginning of spore formation, a septum forms, separating the nascent spore from the rest of the cell and all of the genetic material of the cell is copied into the newly-forming cell.The spore contents are dehydrated and the protective outer coatings are laid down. Once the spore is matured it is released from the cell. On germination, the spore contents rehydrate and a new bacterium emerges and multiplies.

The cycle of spore formation and germination

SPORE STRUCTURE AND ARRANGEMENTS.

General structure of a bacterial Endospore

A = oval, terminal; B = rectangular, terminal; C = rectangular, subterminal,

D = rectangular, central;E = circular, terminal;

F = circular, central;

G = terminal, club-shaped.