BACTERIAL CYTOLOGY and MORPHOLOGY

Learning Objectives

Identify and describe the parts of a bacterial cell and state the function of each bacterial cell structure

Describe the various bacterial shapes and differentiate between the various bacterial cell arrangement and grouping.

Prokaryote vs Eukaryote

Bacterial Cytology

Glycocalyx

Sugar coat

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

protection from dehydration and loss of nutrients.

Capsule

If Glycocalyx is organized and firmly attached to the cell wall

Contributes to bacterial virulence

often protect pathogenic bacteria from phagocytosis by the cells of the host.

Slime Layer

If the substance is unorganized and only loosely attached to the cell wall

Water soluble and is used by the prokaryotic cell to adhere to surfaces external to the cell

Flagella/ Flagellum

are made of protein and appear “whip-like.”

long filamentous appendages that propel bacteria.

Flagella propel the microorganism away from harm and towards food- taxis

Arrangements of flagella:

Atrichous- no flagella

Peritrichous – distributed the entire cell

Monotrichous – single polar

Lophotricous – a tuft of flagella coming from one end

Amphitrichous – flagella at both poles of the cell.

Polar, monotrichous

Pseudomonas

Polar, amphitrichous

Spirillum

Lophotrichous

Spirillum

Peritrichous

Salmonella

3 basic parts

TAXIS

The movement of a bacterium toward or away from a particular stimulus

Chemotaxis- chemical

Phototaxis- light

1. Positive chemotaxis (attractants ): movement towards the stimulus

2. Negative chemotaxis (repellant): movement away from the stimullus

Flagellar movt

Axial Filaments

Unique in spirochetes

Endoflagella

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

Propulsion causes spiral motion or corkscrew movement

FIMBRIAE and PILI

Hairlike appendages shorter, straighter and thinner than flagella

used for attachment and transfer of DNA

Consist of a protein – pilin

FIMBRIAE or Attachment pili

can occur at the poles of the cell or evenly distributed all over

Functions for cell attachment and for bacterial virulence

Pili (sing. Pilus)/ conjugation pili

Sex pili

usually longer than fimbriae

and number only one or two per cell

Motility and DNA transfer- conjugation

Motilty:

a. Twitching motility- short, jerky,

intermittent movements

b. Gliding motility- the smooth gliding

movement of myxobacteria.

Cell Wall

Complex, semi rigid structure responsible for the shape of the cell and serves as a point of anchorage for flagella

prevent bacterial cells from rupturing when the water pressure inside the cell is greater than that ou tside the cell

and serves as a point of anchorage for flagella composed of a macromolecular network called peplidoglycan- murein

PEPTIDOGLYCAN

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

Dissacharide portion:

N-acetylglucosamin (NAG)

N-acetylmuramic acid (NAM)

Gram Positive Cell walls

Consits of many layers of peptidoglycan

Contain teichoic acids-

-consist of an alcohol and phosphate

- cell growth

- antigenic specificity

Classes:

Lipoteichoic acid

wall teichoic acid

Gram negative cell walls

Bacterial cell envelope contains 3 layers(not including the periplasm)

Cytoplasmic membrane/plasma membrane

Periplasm- Peptidoglycan layer

- do not contain teichoic acid

- extremely thin compared to gram positive

Outer cell mebrane

OUTER CELL MEMBRANE (g-ve)

lts strong negative charge is an important factor in evading phagocytosis and the actions of complement

a barrier to certain antibiotics, digestive enzymes such as lysozyme, detergents, heavy metals,bile salts, and certain dyes.

PORIN- permit the passage of molecules

Consists lipopolysaccharide (LPS).

lipopolysaccharide (LPS)

consists of three components:

a. Lipid A- endotoxin

-responsible for the symptoms associated with infections

b. core polysaccharide – provide stability

c. O polysaccharide- antigenic specificity

Grams stain and cell wall

Differences Gram +ve Gram - ve

Atypical cell walls

Mycoplasma- no cell wall

- smallest known bacteria that can grow and reproduce outside living host cells

Acid-Fast Cell walls

High cocentrations (60%) of a hydrophobic waxy lipid (mycolic acid) in their cell wall

Stained using Acid fast staining

- mycobacterium

- nocardia

BACTERIAL MEMBRANE/ CYTOPLASMIC MEMBRANE

Provides a selective barrier between the environment and the cell’s internal structures

regulates the flow of molecules (such as nutrients) into the cell and removes waste from the cell by opening and closing passages called channels

bilayer of phospholipids that has polar and non polar parts-amphipathic

2 KINDS OF PROTEINS

Integral proteins- extends into the lipid bilayer

- typically glycoproteins that act like a molecular signature that cells use to recognize each other

transmembrane protein- regulates the movement of molecules through the cytoplasmic membrane.

Channel protein-forms pores or channels in the cytoplasmic membrane that permit the flow of molecules through the cytoplasmic membrane

Peripheral proteins- are on the inner and outer surface of the cytoplasmic membrane and have the characteristics of a polar and non-polar regions

2 types of transport mechanism

o Passive Transport-moves substances into and out of the cell down a gradient

1. simple diffusion

2. facilitated diffusion

3. osmosis

Active Transport- the movement of a substance across the cytoplasmic membrane against the gradient by using energy provided by the cell

Endocytosis- Large substances enter the cell

Phagocytosis- engulfs solid substances Pinocytosis- engulfs liquid substances

Exocytosis -remove large substances

Cytosol- intracellular fluid of a prokaryotic cell

Nucleoid- where the DNAof the cell is located

Ribosomes- synthesizes polypeptide

-comprised of subunits consisting of protein and ribosomal RNA- rRNA

- identified by their sedimentation rate.

Granule inclusion-free and densely packed, this type of inclusion has many granules each containing specific substances

Vesicle inclusion- commonly found in aquatic photosynthetic bacteria and cyanobacteria

Endospores

are formed by only 2 genera of bacteria,both of which are gram-positive: the aerobic Bacillus and the anaerobic Clostridium.

Endospores are metabolically dormant forms of bacteria that are resistant to heat (boiling), cold, drying and chemical agents.

They have a multilayered protective coat consisting of:

A) A cell membrane

B) cortex- thick peptidoglycan and contains dipicolinic acid (DPA)

C) Another cell membrane

D) A wall of keratin-like protein

E) An outer layer called the exosporium

Spores shape and position

A = oval, terminal;

B = rectangular, terminal;

C = rectangular, subterminal,

D = rectangular, central;

E = circular, terminal;

F = circular, central;

G = terminal, club-shaped.

Bacterial Morphology

coccus (pl ural:cocci, meaning berries)- spherical Diplococci- cocc i in pairs

Streptococci- chain like patterns

Tetrads- divide in two planes and remain in groups of four

Sarcinae- divide in three planes and remain attached in cubelike groups of eight

Staphylococci- divide in mult iple planes and form grapelike dusters or broad sheets

bacillus (plural: bacilli,meaning little staffs)- rod-shaped Diplobacilli appear in pairs after division

streptobacilli occur in chains

Coccobacilli- tapered ends, likecigars. Still others are oval and look so much like cocci

Vibrios- curved rods/ comma shaped

Spirilla- helical shape, like a corkscrew, and fairly rigid bodies

Monomorphic- maintain a single shape

Pleomorphic- they can have many shapes, not just one.

Star shaped cells – Genus Stella

Rectangular flat cells – halophilic Genus Haloarcula