Microbiology: Protists, Monerans, Bacterial Structure

• 9/2/25: Date of the notes.
• Lec. 1 Microbiology: Subject of the notes.

Protists and Monerans

• Protists are referred to as "microorganisms" and reproduce by progeny.
• Monerans are bacteria.
• Viruses are not considered living cells.

Bacterial Cell Structure Basics

• Nucloid is a single circular DNA strand in prokaryotic cells.
• Mycoplasma are the smallest bacteria and lack a cell wall.
• Bacillus anthracis is one of the largest bacteria and is deadly.
• A binomial system uses a (genus species) naming convention, for example, Escherichia coli.
• A genus includes multiple species.
• A virus can have a single name.
• Not all types of bacteria have a capsule.
• Flagella move in fluid medium.

Gram Staining

• Gram staining depends on the pigment color; gram-positive stains blue, and gram-negative stains red.
• Staphylococcus and Streptococcus are gram-positive bacteria.

Differences Between Gram-Positive and Gram-Negative Bacteria

• Gram-positive bacteria have a thick peptidoglycan layer.
• Gram-negative bacteria have a thin peptidoglycan layer.
• Gram-negative bacteria have a periplasmic space, while gram-positive bacteria do not.
• Gram-negative bacteria have an outer membrane with lipopolysaccharides (LPS).
• Gram-positive bacteria have teichoic acid, while gram-negative bacteria do not.

Mycoplasma and LPS

• Mycoplasma species lack a cell wall but are bounded by a cell membrane, stainable by acid-fast staining.
• Lipopolysaccharides (LPS) are located in the outer membrane of gram-negative bacteria and function as endotoxins.
• The cell wall plays a role in the action of antibiotics by breaking down the cell wall of bacteria.

Exotoxins and Endotoxins

• Exotoxin is a toxic substance secreted by bacteria to the outside.
• Endotoxin is a toxic substance secreted by bacteria inside, becoming toxic when the bacteria die.

Peptidoglycan Structure

• The chemical structure contains a sugar backbone and tetrapeptide.
• The sugar backbone is a glycan chain composed of NAM and NAG.
• Tetrapeptide consists of four amino acids attached to NAM by a peptide interbridge that binds alanine with diaminopimetic acid.

Lysozymes

• Lysozymes break the peptidoglycan backbone by breaking the glycosyl bond.
• Lysozymes are present in human tears, mucus, and saliva.
• Lysozymes are considered a natural antibiotic.

LPS Structure and Function

• LPS is an outer membrane component in gram-negative bacteria.
• The endotoxin is an integral part of the cell wall and is secreted from bacteria.
• LPS structure consists of three distinct units.
• Phospholipid (A) consists of a fatty acid + disaccharide + diphosphate group and is the toxic part of LPS.
• The core polysaccharide contains five sugars.
• The outer polysaccharide consists of 25 repeating units consisting of 3-5 sugars.

Cytoplasmic Membrane

• Cytoplasmic membrane surrounds the cytoplasm.
• It is a phospholipid bilayer in eukaryotic cells and contains sterols, except in prokaryotes, except for the genus Mycoplasma.
• Mycoplasma cell membrane is similar to humans but does not contain a cell wall.
• Mycobacteria contains a cell wall and are different from Mycoplasma.
• Mycobacteria have a cell wall, but it's unusual because it contains mycolic acid, a long chain of waxy fatty acid.

Membrane Functions

• Active transport of molecules into or outside the cell.
• Energy generation by oxidative phosphorylation.
• Synthesis of precursors of the cell wall.
• Secretion of enzymes and toxins.
• Active transport requires ATP.
• Passive transport does not require ATP and uses diffusion.
• Facilitated transport passes through channels.

Cytoplasm Composition

• Cytoplasm is composed of 80% water and 20% salts & proteins.
• The cytoplasm of bacteria does not contain organelles.
• The amorphous matrix contains ribosomes, granules, and plasmids.
• The inner matrix contains DNA and nucleoids.
• The nucleoid region is composed of DNA.

Ribosomes

• Ribosomes are sites of protein synthesis.
• Bacterial ribosomes are 70S (50S + 30S).
• Human ribosomes are 80S (60S + 40S).
• Difference in size and shape of ribosomes in bacteria and humans; useful because antibiotics can target the bacterial ribosomes without harming human ribosomes.
• Antibiotics break down the cell wall of bacteria

Granules and Nucleoids

• Granules serve as storage areas for nutrients.
• An example of a granule is "volutin", a granular substance that stains with basic dye and is rich in phosphorus.
• Nucleoids comprise DNA located in the bacteria.
• Prokaryotic DNA is a single circle and contains no nuclear membrane, nucleolus, or mitotic spindle/histones.
• Bacterial DNA has no "introns" but in eukaryotes, DNA does.

Specialized Structures - Capsule

• Capsules are polysaccharide, gelatinous layers.
• Not all bacteria have a (polysaccharide-gelatin) that forms a Capsule structure.
• Bacillus anthracis uniquely has a "D-glutamic acid" capsule.

Importance of Capsules

• Adherence of bacteria to human cells.
• Virulence, limiting the phagocytes' ability to engulf the bacteria.
• Provides identification, acting as an antigen used to identify the bacteria.
• Vaccines utilize capsules to elicit protective bodies.

Flagella Structure and Function

• Flagella are composed of a protein called "flagellin".
• They move bacteria toward nutrients, a process called chemotaxis.
• Motility is driven by ATP.
• If bacteria lack flagella, they are called non-motile bacteria; most cocci lack flagella and are non-motile.

Flagella Types

• Monotrichous: Single flagellum.
• Amphitrichous: Two flagella, at both poles.
• Lophotrichous: Small bunch of flagella at the same site.
• Peritrichous: Flagella all around the bacteria.

Pili (Fimbriae)

• Pili are hair-like filaments that extend from the cell.
• Composed of protein called "pillin."
• Found mainly on gram-negative organisms.
• Pili mediate the attachment of bacteria to receptors on the human cell surface.
• Neisseria gonorrhoeae that doesn't form pili are non-pathogens.
• Sex (F) pilus forms an attachment between male (donor) and female (recipient) bacteria during conjugation.

Glycocalyx

• Glycocalyx is a polysaccharide coating secreted by many bacteria and also called the slime layer.
• It allows bacteria to adhere firmly to skin, heart valves, and catheters.

Spores

• Spores are highly resistant structures formed mainly in two important gram-positive rods "bacteria."
• The Genus Bacillus includes the agent of anthrax.
• The Genus Clostridium includes the agents of tetanus and botulism.
• Spore formation (sporulation) occurs when nutrients such as carbon and nitrogen are depleted.
• Spores form inside the cell and contain DNA, a small amount of cytoplasm, cell membrane, peptidoglycan, little water.
• The spore contains a thick keratin-like coat.
• Spores are resistant to heat, dehydration, radiation, and chemicals.

Spore Properties

• Once the spore is formed, it has no metabolic activity and can remain dormant for many years.
• Upon exposure to water and nutrients, specific enzymes degrade (break) the coat, the water enters, and germination into a pathogenic bacterial cell.
• After the water enters the spore, the germination process begins to form a susceptible bacterial cell.