Bacterial Fine Structures

1. Glycocalyx

2. Flagella

3. Axial Filaments

4. Fimbriae and Pili

Structures External to the Cell Wall

Glycocalyx

• a viscous (sticky) gelatinous polymer that is external to the cell wall and composed of polysaccharide, polypeptide, or both.

• permits the bacterium to adhere to many surfaces, both inanimate and cellular.

1. capsule

2. slime layer

2 types of Structure (Glycocalyx)

Capsule

• if the substance is organized and is firmly attached to the cell wall, the glycocalyx is described as ______

• provide protection against temporary drying by binding water molecules.

• blocks attachment of bacteriophages

• maybe antiphagocytic, i.e, they inhibit the engulfment of pathogenic bacteria by WBC and thus contribute to invasive or infective ability (virulence)

• promote attachment of bacteria to surfaces.

• they may promote the stability of bacterial suspension by preventing the cells from aggregating and settling out, because cells bearing similarly charged surfaces tend to repel one another.

Functions of the Capsule includes:

Slime Layer

• if the substance is unorganized and is loosely attached to the cell wall, the glycocalyx is described as _____

Extracellular Polymeric Substance (EPS)

• a glycocalyx that helps in a biofilm attach to their target environment and to each other is called an ______.

• it protects the cell within it, facilitates communication among them, and enables the cells to survive by attaching to various surfaces in their natural environment.

Flagella

• long hair-like filamentous appendages protruding from the cell wall that propel bacteria.

a. peritrichous

b. polar

-monotrichous

-lophotrichous

-amphitrichous

c. atrichous

The flagella may be ____, _____, or _____

Peritrichous

when the flagella is distributed over the entire cell it is called _____

Polar

when the flagella is at one or both poles or ends of the cell it is called ____

Monotrichous

• a single flagellum at one pole

Lophotrichous

• a tuft of flagella coming from one pole

Amphitrichous

• flagella is at both poles of the cell

Atrichous

when no flagella is present it is called ____

1. filament

2. hook

3. basal body

3 basic parts of Flagella

Filament

• the long outermost region, constant in diameter and contains the globular (roughly sprherical) protein flagellin arranged in several chains that intertwine and form a helix around a hollow core.

Hook

• filament is attached, slightly wider, consisting of different protein.

Basal body

• anchors the flagellum to the cell wall and plasma membrane

• composed of small central rod inserted into a series of rings

• the outer pair of rings is anchored to various portions of the cell wall, and the inner pair of rings is anchored to the plasma membrane.

• run or swim

• tumbles

Various patterns of Motility (the ability of an organism to move by itself)

Run or Swim

• the movement when a bacterium moves in one direction for a length of time

Runs

are interrupted by periodic, abrupt, random changes in direction called tumbles.

Tumbles

are caused by a reversal of flagellar rotation.

Taxis

• the movement of a bacterium towards or away from a particular stimulus

• such stimuli include chemicals (chemotaxis) and light (phototaxis)

Attractant

• if the chemotactic signal is positive, it’s called an ____

• the bacteria move toward the stimulus with many runs and few tumbles.

Repellent

• if the chemotactic signal is negative, it’s called ____

• the frequency of tumbles increases as the bacteria move away from the stimulus.

H antigen

• the flagellar protein called ____, is useful for distinguishing among serovars or variations within a species, of gram negative bacteria.

• for example, there are atleast 50 different H antigens for E. coli.

• Those serovars identified as E. coli O157:H7 are associated with foodborne epidemics.

Axial filaments or Endoflagella

• bundles of fibrils that arise at the ends of the cell beneath an outer sheath and spiral around the cell.

• these structures are only present in spirochetes

• aids in the movement of spiral bacteria.

Periplasmic Flagella

When the exial filament is located within the periplasmic space, it is called

Fimbriae and Pili

• hair-like appendages that are shorter, and thinner than flagella

• consist of protein called pilin arranged helically around a central core.

• attachment

• transfer of DNA, rather than for motility

Fimbriae and Pili are used primarily for:

Fimbriae

• can occur at poles of the bacterial cell or can be evenly distributed over the entire surface of the cell.

• few to several hundred in number per cell.

• they have a tendency to adhere to each other and to surfaces.

Pili

• are longer than fimbriae and usually one or two in number per cell

• they are primarily in DNA transfer but it may also be involved in motility.

Conjugation (Sex) Pili

• F plus or F+

• serves as the port of entry of genetic material during bacterial mating, a process called CONJUGATION.

• some pili play a major role in human infection by allowing pathogenic bacteria to attach to epithelial cell linings of respiratory, genital, or urogenital tracts; prevents bacteria from being washed away by the flow of mucous or body fluids and permit infection to occur.

Cell Wall

• complex, semirigid structure responsible for the shape of the cell.

• surrounds the underlying, fragile plasma (cytoplasmic) membrane and protects it and the interior of the cell from adverse changes in the outside environment.

• to prevent bacterial cells from rupturing when the water pressure inside the cell is greater than outside the cell

• also helps in maintaining the shape of a bacterium

• serves as a point of anchorage for flagella.

Functions of Cell Wall

• peptidoglycan

• polypeptides

General compositions of Cell Wall

Peptidoglycan

• also known as murein, from murus meaning WALL

• consists of a repeating disaccharide attached by polypeptides to form a lattice that surrounds and protects the entire cell.

• N-acetylglucosamine (NAM)

• N-acetylmuramic acid (NAG)

Disaccharide portion (glycan) is made up of monosaccharides called

Polypeptides

• peptide portion of peptidoglycan that links or connects the rows of disaccharides (glycan portion)

• cross-linking interface is interfered by Penicillin and Cephalosporin

• Teichoic acid

• Periplasm

Unique compositions

Teichoic acid

• in gram-positive, cell wall also contains ____ which consists primarily of an alcohol (such as glycerol or ribitol) and phosphate.

Lipoteichoic acid

• spans throughout the entire thickness of the peptidoglycan and glycolipids of the plasma membrane

Wall teichoic acid

• glycan chains of the peptidoglycan layer only

Periplasm

• in gram-negative, cell wall also contains a gel-like fluid known as _____, in between the plasma membrane and outer membrane.

• evading phagocytosis and the actions of complement (lyses cells and promotes phagocytosis), two components of the defenses of the host.

• provides a barrier to certain antibiotics (for example, penicillin), digestive enzymes such as lysozyme, detergents, heavy metals, bile salts, and certain dyes.

• permit the passage of molecules such as nucleotides, disaccharides, peptides, amino acids, vit. B12, and iron through PORINS.

Functions of Periplasm

Lipopolysaccharides (LPS)

• large complex molecule that contains lipids and carbohydrates and consists of 3 components which are lipid A, core polysaccharide, and O polysaccharide (somatic)

Lipid A

• lipid portion of the LPS and is embedded in the top layer of the outer membrane; ENDOTOXIN

Core polysaccharide

• attached to lipid A and contains unusual sugars; structural-to provide stability

O polysaccharide (somatic)

• functions as an antigen (O-Ag) and is useful for distinguishing species of gram-negative bacteria.

1. Wall-less bacteria

2. Acid-fast bacteria

3. Chlamydia

Atypical Cell Wall

Wall-less bacteria

• members of the Genus Mycoplasma and related organisms have no walls or have a little wall material.

• their plasma membranes are unique among bacteria in having lipids called sterols which are thought to help protect them from lysis (rupture)

Mycoplasmas

• are the smallest known bacteria that can grow and reproduce outside living host cells

Acid-fast Bacteria

• members of the Genus Mycobacterium and Nocardia

• these bacteria contain high concentrations (60%) of a hydrophobic waxy lipid (mycolic acid) in their cell wall

• the mycolic acid forms a layer outside of a thin layer pf peptidoglycan

• the hydrophobic waxy cell wall causes both cultures of Mycobacterium spp. to clump and to stick to the walls of the flask.

Chlamydia

• intracellular parasites similar to Gram-negative bacteria but they lack a peptidoglycan layer between the outer and inner membrane leaflets.

• Their life cycle is unique as they alternate between two morphologically different forms: Elementary Bodies, Intermediate Bodies, Reticulate Bodies.

1. division Gracilicutes - Gram-negative

2. division Firmicutes - Gram-positive

3. division Tenericutes - without cell wall

4. division Mendosicutes - Archaeobacteria

4 Divisions of Bacteria (cell wall characteristics)

1. Cell Membrane / Cytoplasmic membrane / Plasma membrane

2. Cytoplasm

3. Nucleoid

4. Ribosomes

5. Inclusions

6. Endospores

Structures Internal to the Cell Wall

Cell Membrane / Cytoplasmic membrane / Plasma membrane

• a thin structure lying inside the cell wall and enclosing the cytoplasm of the cell

• serve as a selective barrier through which materials enter and exit the cell

• the plasma membrane of prokaryotes consists primarily of phospholipids, which are the most abundant chemicals in the membrane, and proteins.

• the phospholipid molecules are arranged in two parallel rows called a Lipid Bilayer

• the polar heads are on the two surfaces of the lipid bilayer, and the nonpolar tails are in the interior of the bilayer.

• peripheral proteins

• integral proteins (transmembrane proteins, glycoproteins, glycolipids)

Protein molecules in the membrane can be arranged in a variety of ways:

Cytoplasm

• refers to the thick, aqueous, semitransparent, and elastic substance of the cell inside the plasma membrane

• it is about 80% water and contains primarily proteins (enzymes), carbohydrates, lipids, inorganic ions, and many low molecular-weight compounds

• the major substances in the cytoplasm of prokaryotes are a nucleoid (containing DNA), particles called ribosomes, and reserve deposits called inclusions.

1. cytoplasmic area

2. chromatic area

3. fluid portion

Cytoplasm is divided into:

Cytoplasmic area

• granular in appearance and rich in macromolecular RNA protein bodies known as ribosomes.

Chromatic area

• rich in DNA

Fluid portion

• which dissolves the substance

Nucleoid

• usually contains a single long, continuous, and frequently circularly arranged thread of double-stranded DNA called the bacterial chromosome.

• bacteria often contain small usually circular, double-stranded DNA molecules called Plasmids.

• capable of autonomous replication and encode many auxiliary functions such as antibiotic resistance which are usually not necessary for bacterial growth.

• many plasmids can be transferred from one bacterium to another by a process called conjugation (sex pilus)

• antibiotic resistance

• tolerance to toxic metals

• the production of toxins

• the synthesis of enzymes

Plasmids carry genes for activities such as:

Ribosomes

• serves as a site of protein synthesis

• are composed of two subunits, each of which consists of protein and a type of RNA called ribosomal RNA (rRNA)

• the subunits of a 70s ribosome are a small 30S subunit containing one molecule of rRNA and a larger 50S subunit containing two molecules of rRNA.

Inclusions

• several kinds of reserve deposits within the cytoplasm of the prokaryotic cells

Metachromic granules

• are large inclusions that take their name from the fact that they sometimes stain red with certain blue dyes such as methylene blue.

• Volutin represents a reserve of inorganic phosphate (polyphosphate) that can be used in the synthesis of ATP

• found in algae, fungi, and protozoa, as well as in bacteria.

Polysaccharide Granules

• typically consists of glycogen and starch, and their presence can be demonstrated when iodine is applied to the cells

• in the presence of iodine, glycogen granules appear reddish brown and starch granules appear blue.

Lipid Inclusions

• appear in various species of Mycobacterium, Bacillus, Azotobacter, Spirillum and other genera.

• are revealed by staining cells with fat-soluble dyes, such as Sudan dyes.

Sulfur granules

• energy reserve for some bacteria

• genus Thiobacillus — derive energy by oxidizing sulfur and sulfur-containing compounds

Carboxysomes

• contain the enzyme ribulose 1,5-diphosphate carboxylase that is needed for carbon dioxide fixation

• among the bacteria containing carboxysomes are nitrifying bacteria, cyanobacteria, and thiobacilli.

Gas vacuoles

• hollow cavities found in many aquatic prokaryotes

• maintain buoyancy so that the cells can remain at the depth in the water appropriate for them to receive sufficient amounts of oxygen, light, and nutrients.

Magnetosomes

• inclusions of Iron oxide (Fe3O4) surrounded by invaginations of the plasma membrane

• bacteria may use these to move downward until they reach a suitable attachment site.

Endospores

• specialized “resting” cells formed by Gram-positive bacteria when essential nutrients are depleted

• are highly durable dehydrated cells with thick walls and additional layers

• they are formed internal to the bacterial cell membrane

• conatins a large amount of an organic acid called dipicolinic acid (DPA), which is accompanied by a large number of calcium ions.

• can remain dormant for thousand of years

• returns to its vegetative state by a process called GERMINATION and is usually triggered by physical or chemical damage to the endospore’s coat.

Sporulation or Sporogenesis

• the process of endospore formation within a vegetative cell and usually takes several hours to form

Stage 0

Stage 1

Stage 2

Stage 3

Stage 4

Stage 5

Stage 6

Stage 7

Stages of Spre Formation

Stage 0

• at initiation of sporulation, the vegetative cell contains 2 chromosomes

Stage 1

• the 2 chromosomes subsequently condenses to form a single broad filament

Stage 2

• the chromosomes separate, and one moves terminally in the cell. This is followed by the formation of a septum between the two, but without cell wall formation

Stage 3

• the larger of the protoplasts engulfs the smaller; the smaller protoplast, or forespore, then lies within the cytoplasm of the larger and is surrounded by two membranes

Stage 4

• characterized by the development of the cortex between the two membranes. During this stage, the spore becomes refractile to transmitted light. Deposition of Ca DPA also takes place.

Stage 5

• the multiple layers of the spore coat are laid down

Stage 6

• spore continues to mature and becomes increasingly heat resistant

Stage 7

• release of the spore when the mother cell lysis.