BIO 411 Chapter 3 – Bacterial Morphology and Cell Wall Structure and Synthesis

Prokaryote vs. Eukaryote  Get with a partner and make a list of the differences between Prokaryotes and Eukaryotes.  List differences on board  Amazing cell size demo!

Shapes of Bacteria  Almost all bacteria have one of three morphologies (or shapes):  coccus - spherical-shaped (pl., cocci)  Diplococcus  Streptococcus  Staphylococcus  bacillus - rod-shaped (pl., bacilli)  spirillum - spiral-shaped (pl., spirilla)  Figure 3-3 B

Gram Stain  Gram Stain  Crystal violet  Iodine  Decolorizer (EtOH or Acetone)  Safranin  Gram + vs. Gram – cells  “P” – purple, positive  Figure 3-3 A  Only dependable on new cultures (24hr)

Bacterial Cell Structure  Typical prokaryotic cell - Figure 3.1  Inside-Out Approach  What is the cytoplasm?  ~80% water

Cytoplasm  Also contains:  The bacterial chromosome (structure?)  It is about 1mm long (1000X longer than the cell)  It’s localized in the nucleoid  Plasmids – small circular pieces of non- chromosomal DNA  Functions?  Ribosomes (70S) – function?  Protein synthesis

Cytoplasm  Cytoplasmic membrane – typical lipid bilayer  Carries out many functions associated with eukaryotic organelles  Mesosome – anchor to separate daughter chromosomes during cell division  Figure 3-1

Bacterial Cell Structure (cont.)  Next layer: Bacterial Cell Wall  Composed of sub-units found nowhere else in nature  site of action of some of the most effective antibiotics  cell wall determines a cell’s morphology  Primary Function – protect cell from exploding (osmotic pressure)!!!

Bacterial Cell Structure (cont.)  Cell Wall Structure  Bacterial cell walls are composed of peptidoglycan  the glycan portion of peptidoglycan is made of a huge polymer of carbohydrates containing:  N-acetylmuramic acid (NAM) and  N-acetylglucosamine (NAG)  These long chains of alternating NAM and NAG are held together by short peptide cross-bridges  log raft analogy

Gram+ vs. Gram- Cell Walls  Gram+ cells have a very thick, multilayered cell wall  they also contain teichoic acids and lipoteichoic acids  Lysozyme  Figure 3-2 A  Gram- cells have a very thin layer of peptidoglycan  they also have an outer membrane in addition to the cytoplasmic membrane  the space between these two membranes is called the periplasmic space or periplasm

Gram+ vs. Gram- Cell Walls (cont.)  the outer membrane is an asymmetric bilayer:  Phospholipids on the inside  lipopolysaccharides (LPS) on the outside  LPS structure:  Lipid A - also called endotoxin because it damages cells and tissues (also causes fever and shock)  Core Polysaccharide  O antigen – distinguishes serotypes of a species (E. coli O157:H7)  Figure 3-10

Gram+ vs. Gram- Cell Walls (cont.)  Porins allow non-specific transport across the membrane  Figure 3-2 B  Basis for the Gram stain reaction (Figures 3-2 and 3-3 A)

Bacterial Cell Structures  Capsule outer coating of sticky polysaccharide or protein  Also called a glycocalyx or slime layer  Functions?  Antiphagocytic and poorly antigenic - Streptococcus pneumoniae  Adherence - Streptococcus mutans and dental caries, many other examples too!  Biofilm - protection

Movement of Prokaryotic Cells  Flagella - ropelike propeller composed of flagellin  Chemotaxis  bacteria can move toward nutrients or away from toxic substances  Mechanism – “swim and tumble”

Attachment of Prokaryotic Cells  Bacteria can use fimbriae and pili to attach to surfaces and other cells  fimbriae are numerous, short protein filaments of attachment (E. coli and Neisseria gonorrhoeae)  pili are long protein filaments for attachment of bacteria to other bacterial cells  Used for DNA transfer  Figure 3-4

Mycobacteria and Mycoplasmas  Mycobacteria have a peptidoglycan cell wall, but they contain an outer covering of mycolic acid  Antiphagocytic  Acid-fast stain  Mycoplasmas do not have a cell wall

Bacterial Endospores  Some types of Gram+ bacteria have the ability to form endospores  Primary genera Bacillus and Clostridium  the endospore is the “navy seal” of living organisms  Vegetative State vs. Endospore  Endospore production – Figure 3-12

Bacterial Endospores (cont.)  Endospore germination  Important Point:  endospores are not a means of reproduction  Importance of endospores

Disease of the Day  Anthrax  Etiology – Bacillus anthracis (via toxins)  Aerobic, endospore-forming,  Reservoir – Contaminated animals (herbivores) and animal products  Transmission and Development  Cutaneous anthrax – through a cut in the skin  Figure 25-3, page 268  20% mortality w/o treatment, less than 1% with  Gastrointestinal anthrax – rare (~100% mortality)

Disease of the Day  Inhalational or Pulmonary anthrax – endospores inhaled  Can show 2 or more months of latency  Days 1-2 mild fever, cough, chest pain (non-specific)  Death usually occurs within 3 days w/o treatment  Almost 100% mortality  Lab ID: microscopy and specific antigen detection  Prevention and Control  vaccine (6 initial + yearly booster)  antibiotics effective if given in time

Cell Structure Review  Find a partner and review the structure of bacterial cells

Endosymbiosis  The Theory of Endosymbiosis  Supporting Evidence:  Mitochondrial DNA  70S ribosomes  Binary Fission  RNA sequencing