Microbial Cell Structure and Function

• Microbial Morphology is the study of the size, shape, and arrangement of a living organism
• Cellular morphology is the study of the size and shape of the cell
• Typical bacteria is less than 3 μm in size
• Cocci is 0.5 to 3 μm in diameter
• Bacilli is 0.15 to 2 μm in width and 0.5 to 20 μm in length
• Bacterial Shapes: Coccus - spherical and ovoid, Bacillus - cylindrical, Spiral - curve or loose spiral
• Bacterial Arrangement: Singly - singular, Strepto - in chain, Staphylo - in cluster, Diplo - in pairs, Sarcinae - three-dimensional cubes, Spirochetes - tightly coiled, Pleomorphic - no definite shape and/or arrangement
• Prokaryotic Cell is exhibited by organisms falling under Domain Bacteria and Domain Archaea
• Cell Membrane: Gatekeeper for the entrance and exit of dissolved substances, Selective permeability, Anchorage, Energy conservation and consumption
• Bacterial Membrane: Phospholipid bilayer containing embedded proteins, Composed of hydrophobic tails (fatty acids) and hydrophilic head (glycerol molecule containing phosphate), Hopanoids - Strengthened sterol-like molecules present in bacteria or eukaryotic cells when there is an absence of cell wall, Archaeal membrane
• Cell Wall: Gives shape and rigidity on the cell, Confers structural strength on the cell to keep it from bursting due to osmotic pressure, Contributes to pathogenicity, Site of action of several antibiotics
• Lysozyme: Weakens the peptidoglycan and causes cell lysis, Acts as a major line of defense against bacterial infection which are present in human secretions including tears, saliva, and other bodily fluids, Destroys pre-existing peptidoglycan, penicillin blocks a key step in its biosynthesis
• Peptidoglycan: Made up of rigid polysaccharide, Not present in Archaea and Eukarya, Composed of alternating repeats of N-acetylglucosamine and N-acetylmuramic acid, 90% of cell wall in a Gram positive bacteria and form many layers
• Teichoic acid: Embedded in the cell wall and function to bind divalent metal ions, such as Ca2+ and Mg2+, prior to their transport into the cell
• Lipoteichoic acid: Covalently bonded to membrane lipids rather than to peptidoglycan
• LPS or lipopolysaccharide: Small amount of peptidoglycan in cell wall of Gram negative, Has two components: core polysaccharide and O-specific polysaccharide, Outer membrane is found in second lipid bilayer
• Periplasm: The space located between the outer surface of the cytoplasmic membrane and the inner surface of the outer membrane, Spans about 15 nm, Porins - Channels for the entrance and exit of solutes (Nonspecific porins and Specific porins)
• Cell Wall Differences: Gram-positive bacteria, Gram-negative bacteria
• Archaeal Cell Wall: Methanogens have pseudomurein and other polysaccharide cell walls, Pseudomurein = peptidoglycan with N-acetylglucosamine and N-acetyltalosaminuronic acid, S-Layer - Paracrystalline surface layer, most common type of cell wall in Archaea
• Cell Surface Structure: Glycocalyx, Capsule, Slime, Fimbriae, Pili, Hami
• Glycocalyx organized in a tight matrix that excludes small particles and is tightly attached
• Slime or slime layer: More easily deformed and loosely attached, It will not exclude particles, More difficult to see microscopically
• Fimbriae: Thin filamentous structures made of protein that extend from the surface of a cell, 2-10 nm in diameter, Enable cells to stick to surfaces, Form pellicles or biofilms on solid surfaces
• Pili: Typically longer and only one or a few pili are present on the surface of a cell, All Gram negative produce pili while many Gram positive contain pili, Can be receptors for certain types of viruses, they can be easily seen under the electron microscope when they become coated with virus particles
• Functions of the Pili: Adhesion, Conjugation
• Hamus or Hami: Unique attachment structure resembles a tiny grappling hook, Affix cells to a surface to form a networked biofilm, Prevent cells from being washed away in groundwater flowage
• Cell Inclusions: Poly-β-hydroxybutyric acid (PHB), Glycogen, Polyphosphate granules, Elemental sulfur, Carbonate, Magnetosomes
• Gas Vesicles: Conical-shaped structures made of protein, Length: 300-1000 nm, Width: 45-120 nm, Appears as irregular bright inclusions seen in light microscopy or transmission electron microscope, Primitive form of vacuoles
• Gas Vesicle Proteins: GvpA (major protein) - Forms the watertight vesicle shell and is a small, hydrophobic, and very rigid protein, GvpC (minor protein) - Strengthens the shell of the gas vesicle by cross-linking
• Endospores: Highly differentiated cells that are extremely resistant to heat, harsh chemicals, and radiation, Serve as survival structures and enable the organism to endure unfavorable growth conditions, Visible by light microscopy as strongly refractile structures and through electron microscopy, Visualized through special staining techniques such as Schaeffer-Fulton spore staining
• Parts of Endospore: Exosporium - outermost layer providing outer covering, Spore coats - innermost layer where spore-specific protein is located, Cortex - consists of loosely cross-linked peptidoglycan, Core - contains the core wall, cytoplasmic membrane, cytoplasm, nucleoid, ribosomes, and other cellular essentials, Dipicolinic acid - found in endospores but not in vegetative cells
• Endospore Formation: Dormant stage of a bacterial life cycle, Vegetative cell > endospore > vegetative cell, Bacillus spp. and Clostridium spp.
• Steps in Vegetative Cell Process: Activation - Occurs when endospores are heated for several minutes at an elevated but sub-lethal temperature, Germination - Rapid process (occurring in a matter of minutes), is signaled by the loss of refractility of the endospore and loss of resistance to heat and chemicals, Outgrowth - involves visible swelling due to water uptake and synthesis of RNA, proteins, and DNA
• Schaeffer-Fulton spore staining is staining technique used to visualize endospores
• Malachite green is stain used in Schaeffer-Fulton spore staining, infused into the spore with steam
• Endospore is dormant stage of a bacterial life cycle
• Dipicolinic acid is found in endospores but not in vegetative cell
• Endospore formation is vegetative cell > endospore > vegetative cell
• Vegetative cell process: Activation, Germination, Outgrowth
• Activation occurs when endospores are heated for several minutes at an elevated but sub-lethal temperature