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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