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Basic Bacteriology Bacteria Bacteria are single-celled organisms Contain no membrane bound nucleus Termed prokaryotes = pre nucleus Pro = pre karyote = nucleus Do not contain any other organelles (such as ER or Golgi or mitochondria) Cytoplasm is surrounded by a lipid membrane with is surrounded by a rigid cell wall DNA bundled in a region called the nucleoid The Bacterial Cell Flagella Ribosomes Capsule Cell wall Plasma membrane Nucleoid region (DNA) Pili The Bacterial Cell Nucleoid DNA Bacterial Nomenclature Binomial naming system Two word naming system First word is genus name Always capitalized Escherichia Second word is species name Not capitalized coli When writing full name genus usually abbreviated E. coli Full name always italicized Or underlined Bacterial Morphology Morphology classification by shape Morphology is often expressed in the binomial naming system Ex. Bacillus subtillis, the word Bacillus means rod Ex. Streptococcus pyogenes, Streptococcus means a chain of spheres Ex. Helicobacter pylori, helix shaped bacterium Many names of bacteria do not reference there shape such as E. coli, Pseudomonas aeruginosa, or Burkholdaria cepacia. Bacterial Morphology Examples of Morphology • Bacteria exhibit a variety of shapes • Coccus • Spherical • Bacillus • Rod or cylinder shaped Examples of Morphology • Other shapes • Coccobacillus • Short round rod • Vibrio • Curved rod • Spirillum • Spiral shaped • Spirochete • Helical shape Bacterial Anatomy and Structures Cytoplasm- fluid that fills the cell where most reactions and activities of the cell take place Cell Membrane- barrier between the internal cell fluid (cytoplasm) and the exterior environment. It is selectively permeable only allowing in selected comounds Cell Wall- rigid structure surrounding the cell membrane that gives bacteria there shape. Stronger than the cell membrane helps hold the cell together and maintain structural integrity. The cell wall can be of varying degrees of thickness depending on the type of bacteria Cell capsule- slime layer that protects bacteria and helps bacteria to adhere to surfaces Bacterial Anatomy and Structures Nucleoid region- location of the genetic material (DNA) in the bacterial cell. Typically bacterial DNA is one large circular DNA molecule that is packed together by supercoiling. *Bacterial DNA should not be referred to as a chromosome because it is not packed together using chromatin and does not resemble the organization of DNA in eukaryotes. The alternate name for bacterial DNA is genophore Plasmid- a small genetic element of circular DNA that is separate and distinct from the nucleoid DNA. The plasmid is typically thousands of times smaller than the nucleoid DNA but often very important as it may carry genes for antibiotic drug resistance Bacterial Anatomy and Structures Flagella- long structure made of protein that propels the bacteria when it spins. Pili- structure made of protein subunits that extend out of the cell. Function for attachment to surfaces and gliding motility. Inclusions- small structure used to store excess material typically as nutrient reserve. Stored materials include phosphates, polysaccharides, nitrogen, sulfur, proteins and biopolymers Ribosome- a structure consisting of protein and rRNA. It translates mRNA into a sequence of amino acids (proteins) Size Distribution Size in the Microbial World Tremendous range in size Smallest virus approximately 1/1,000,000th size of largest eukaryotic cell Prokaryotic Cells Comparing Prokaryotic and Eukaryotic Cells Prokaryote comes from the Greek words for prenucleus. Eukaryote comes from the Greek words for true nucleus. Prokaryote Eukaryote One circular chromosome, not in a membrane No histones No organelles Peptidoglycan cell walls Binary fission Paired chromosomes, in nuclear membrane Histones Organelles Polysaccharide cell walls Mitotic spindle Average size: 0.2 -1.0 µm 2 - 8 µm Basic shapes: Unusual shapes Star-shaped Stella Square Haloarcula Most bacteria are monomorphic A few are pleomorphic Figure 4.5 Arrangements Pairs: diplococci, diplobacilli Clusters: staphylococci Chains: streptococci, streptobacilli Glycocalyx Outside cell wall Usually sticky A capsule is neatly organized A slime layer is unorganized & loose Extracellular polysaccharide allows cell to attach Capsules prevent phagocytosis Figure 4.6a, b Flagella Outside cell wall Made of chains of flagellin Attached to a protein hook Anchored to the wall and membrane by the basal body Figure 4.8 Flagella Arrangement Figure 4.7 Figure 4.8 Motile Cells Rotate flagella to run or tumble Move toward or away from stimuli (taxis) Flagella proteins are H antigens (e.g., E. coli O157:H7) Motile Cells Figure 4.9 Axial Filaments Endoflagella In spirochetes Anchored at one end of a cell Rotation causes cell to move Figure 4.10a Fimbriae allow attachment Pili are used to transfer DNA from one cell to another Figure 4.11 Cell Wall Prevents osmotic lysis Made of peptidoglycan (in bacteria) Figure 4.6a, b Peptidoglycan Polymer of disaccharide N-acetylglucosamine (NAG) & N-acetylmuramic acid (NAM) Linked by polypeptides Figure 4.13a Figure 4.13b, c Gram-positive cell walls negative cell walls Gram- Thick peptidoglycan Teichoic acids In acid-fast cells, contains mycolic acid Thin peptidoglycan No teichoic acids Outer membrane Gram-Positive cell walls Teichoic acids: Lipoteichoic acid links to plasma membrane Wall teichoic acid links to peptidoglycan May regulate movement of cations Polysaccharides provide antigenic variation Figure 4.13b Gram-Negative Outer Membrane Lipopolysaccharides, lipoproteins, phospholipids. Forms the periplasm between the outer membrane and the plasma membrane. Protection from phagocytes, complement, antibiotics. O polysaccharide antigen, e.g., E. coli O157:H7. Lipid A is an endotoxin. Porins (proteins) form channels through membrane Gram-Negative Outer Membrane Figure 4.13c Gram Stain Mechanism Crystal violet-iodine crystals form in cell Gram-positive Alcohol dehydrates peptidoglycan CV-I crystals do not leave Gram-negative Alcohol dissolves outer membrane and leaves holes in peptidoglycan CV-I washes out Atypical Cell Walls Mycoplasmas Lack cell walls Sterols in plasma membrane Archaea Wall-less, or Walls of pseudomurein (lack NAM and D amino acids) Damage to Cell Walls Lysozyme digests disaccharide in peptidoglycan. Penicillin inhibits peptide bridges in peptidoglycan. Protoplast is a wall-less cell. Spheroplast is a wall-less Gram-positive cell. L forms are wall-less cells that swell into irregular shapes. Protoplasts and spheroplasts are susceptible to osmotic lysis. Plasma Membrane Figure 4.14a Plasma Membrane Phospholipid bilayer Peripheral proteins Integral proteins Transmembrane proteins Figure 4.14b Fluid Mosaic Model Membrane is as viscous as olive oil. Proteins move to function Phospholipids rotate and move laterally Figure 4.14b