Understanding Bacterial Structures and Functions

1. Chapter 4 Bacterial Structure and Growth

2. Bacteria • Bacteria can be classified by their morphology (shape), stain reactions, atmospheric requirements, growth needs, organization, physical and biochemical composition and antigenic structure.

3. MorphologyShapes and Arrangements (Pg 122 – 124) • Three common shapes • Bacilli (rod) • Long as 20 µm or as short as 0.5 µm • Cocci (sphere) • Kokkos meaning “berry” • 0.5 to 1.0 µm • Spirochetes (spiral) • 1 to 100 µm in length

5. Structure of Bacteria Pg. 122 to 139

6. Flagella • Motility – is the independent movement of an organism. • In bacteria movement is carried out by flagella. • Each flagella is composed of a filament, hook and basal body.

7. Flagella • The long filament is composed of a helical protein strand. • Subunits of the protein filaments are called flagellin. • The filament is anchored into the cell membrane by hook which is attached to the basal body. • Basal body is made up of 20 protein that forms a central rod and closing rings. • There can be two to four rings making up the basal body. • Range in length 10 to 20 um and 20nm thick • To view need to stain

8. Arrangement of Flagella • Monotrichous – single flagellum at one end. • Lophotrichous – two or more flagella at one end. • Amphitrichous – single or group of flagella at both ends. • Peritrichous – flagella over the whole cell surface.

9. Movement • Flagella spin counter-clockwise to move the bacteria forward. • The flagella reverse (Clock-wise) to move the bacteria back. • The backward movement is more like a tumble that helps change direction not backup the bacteria. • Most movement is stimulated by chemicals and light and is known as taxis • Light taxis • Chemotaxis

10. Pili (Fimbriae) • Structures used for attachment to specific surfaces. • Many Gram negative bacteria have pili. • Short hair like fibers. • Made up of protein subunits called pilin. • Have protein adhesion located at the tip of the pili that bind to different animal tissue. • Neisseria gonorrhoeae pili attach to urogenital tract (or toilet seat).

12. Conjugation Pili • True pili is used in conjugation (transfer of DNA from one bacteria to another). • It is a tube that attaches to a bacteria. • The DNA is moved down the tube from the donor to the receiver.

14. Capsule (Glycocalyx) • Many bacteria have capsules. • Bacteria will secrete layer of polysaccharides and proteins. • The capsule serves as a buffer between the bacteria and the environment to prevent dehydration. • It also helps to attach the cell to each other and to host (V. cholerae to intestinal wall). • Protects some bacteria from being engulfed by white blood cells.

16. Cell Wall • All bacteria except for Mycoplasma have a cell wall. • A cell wall protects the bacteria and gives it its shape. • Major role is to prevent lysis (bursting) due to osmotic pressure. • Cells have more dissolved material inside them then is found in the surrounding environment. • This hypertonic condition would cause water to move into the cell an increase the pressure inside. • Without the cell wall the bacteria would burst.

17. Cell Wall • Eubacteria cell walls are made up of a network of peptidoglycan chains. • Peptidoglycan is made up of alternating units of two amino containing sugars. • N-acetylglucosamine (NAG) • N-acetylmuramic acid (NAM) • This carbohydrate backbone is held together by side chains of four amino acids. • Plus polypeptide cross-linkage

18. Cell Wall Gram-Positive Bacteria • Gram-positive bacteria have thick layered peptidoglycan wall. • 60 to 90 % made up of peptidoglycan. • Peptidoglycan layer also has a anionic polysaccharide called teichoic acid. • Helps to link peptidoglycan layers together. • Penicillin interferes with the construction of the peptidoglycan layer.

19. Insert Picture of Peptidoglycan

20. Cell Wall of Gram-Negative Bacteria • Gram-negative bacteria have a multilayered cell wall. • No teichoic acid. • Peptidoglycan layer much thinner. • Peptidoglycan makes only 10% total of cell wall.

21. Gram-negative Cell Wall Layers • Outer membrane • Made up of bilayer. • Inner layer of phospholipids. • Outer layer of lipopolysaccharides (LPS). • Contains proteins porins • Porins form pores in the outer membrane. • Allows small molecules to move through the cell wall. • Inner layer is made up of peptidoglycan.

23. Gram-Negative Cell Wall LPS • Lipopolysaccharide (LPS) are not found in any other organism. • The lipid portion (lipid A) is found in the outer membrane bi-layer. • Lipid A portion is a endotoxin • When the bacteria die they breakdown and the LPS is released and causes fever and circulatory collapse. • The polysaccharide is a O-polysaccharide • Used to identify bacteria ie O157:H7

26. Bacterial Cell Membrane • Boundary between cytoplasm and external environment. • Act as a permeability barrier to hold bacterial cytoplasm inside the cell. • Also acts to transport nutrients in and waste out of the cell. • Made up of 40% phospholipids and 60% proteins. • Phospholipids are arranged in two parallel layers (bi-layer).

27. Cell Membrane • Proteins in the membrane can be used for synthesis of the membrane. • Also, some of these proteins are used for energy production (ATP). • Other proteins act as transporters of charged molecules in and out of the bacteria.

28. Cytoplasm (Pg 135 to 136) • Cytosol a gelatinous mass of proteins, amino acids, sugars, nucleotides, salts, vitamins and ions. • Structures • Ribosomes hundreds of thousands in bacteria • Made of RNA and protein • Used for protein synthesis

29. Cytoplasm • Inclusion bodies • Store nutrients or monomers for bacterial structures • Metachromatic granules – phosphate depots • Magnetosome crystals of iron-containing molecules magnetite. • Help align bacteria to magnetic fields • Nucleoid – chromosome region • No membrane DNA aggregates and no ribosomes are found in that area. • Plasmids – small circular DNA • Can be one or more • 5-100 genes • Important function in causing disease

30. DNA Plasmids • Some plasmids carry genes for drug resistance. • R-plasmids (R = “resistance”). • These plasmids can be transferred between bacteria during conjugation.

31. Endospores • A few Gram-positive bacteria produce a highly resistant structures called endospores (spores). • Bacillus and Clostridium Genusesare of major concern in human bacterial infections and are spore produces. • Endospores will be produced by these bacteria due to nutritional or environmental pressures. • Endospores are one of the most resistant living things known.

32. Endospores • Little water and undergo few chemical reactions. • Have some ribosomes and enzymes. • Has an unique organic substance called dipicolinic acid. • Dipicolinic acid helps stabilize proteins and DNA. • Helps to make spores viable at 100ºC for 2 hr.

33. Endospore

35. Diseases Caused by Spore Forming Bacteria • Anthrax caused by Bacillus anthracis. • Botulism, gas gangrene and tetanus caused by different Clostridium species. • Clostridium difficile when you take antibiotics this bacteria can overpopulate your intestine or colon and can cause colitis.

37. Bacterial Reproduction (Pg 141 – 142) • Almost all bacteria reproduce by binary fission. • In binary fission: • Cell elongates and DNA replicates. • The two DNA strands are attached to the cell membrane and separated by new membrane growth. • The new membrane pinches inward. • The cell membrane thickens. • The cell wall divides.

39. Generation Time • Generation Time - Is the interval of time between successive binary fission of a cell. • Escherichia coli generation time 20 minutes. • Staphylococcus aureus 30 minutes. • Mycobacterium tuberculosis 15 hours. • Treponema pallidum (Syphilis) 33 hours.

40. How Many E. coli Would There Be After 2 Days? • E. coli generation time is every 20 minutes • 3 generations per hour • 48 hour period • N(t) =N(0)2n N(48) = (1) x 2144 • N(48) = 2144 • 2144 = 2.2 x1043 • 109 = 1,000,000,000 • Each bacteria is 10-12 gms • The total bacterial mass from 2.2 x1043 = 1031 gms. • 454 gms = 1 pound • The mass would be 24,000,000,000,000,000,000,000,000 tons • or 400 x the mass of the earth

41. Bacterial Growth (Pg 143 – 149) • Four distinctive phases Lag phase Logarithmic phase Stationary Phase Decline Phase

42. Lag Phase • Bacteria adapts to its new environment. • There is no cell division • Bacteria: • Grow in size • Store nutrients • Synthesize enzymes

43. Logarithmic Phase (Log) • Bacteria enter an active phase of growth. • Exponential growth occurs by binary fission. • In infection disease symptoms develop in animals or humans when the bacteria are in log phase. • Toxin production causes tissue damage. • Fever, coughing. • However, bacteria are most susceptible to antibiotics in this phase because they are producing new cell walls.

44. Stationary Phase • Point where death rate equals reproduction. • Immune system is killing large numbers. • Nutrients are running low. • Waste products accumulate. • Oxygen may be running out.

45. Death Phase • Dying cells exceeds reproduction. • Some cells, Bacillus and Clostridium, may have produced endospores and will enter dormancy. • Others will end here. • Bacterial Growth

46. Physical Requirements for Bacterial Growth • Temperature • Each bacteria has an optimal growing temperature. • Also, a 30ºC range at which growth can occur. • Reduced growth is the result of slower reaction times for enzymes. • Three Groups • Psychrophiles • Thermophiles • Mesophiles

47. Temperature • Psychrophiles • Psychro = “Cold” Philes = “Loving” • Optimum growth rate 15ºC • Can grow at 0ºC - 20ºC • Unsaturated fats in phospholipids so they stay fluid at lower temperatures. • Thermophiles • Optimum temperature 60ºC • Growth at 40ºC - 70ºC • Compost heaps, hot tubs, hot springs • Highly saturated fats to stabilize structures and heat stable enzymes.

48. Temperature • Mesophiles • Middle temperature range 20ºC - 42ºC • Includes the pathogens • Get slow growth with some at low temperatures 5ºC • Not true psychrophiles so referred to as psychrotrophic • Psychrotrophic – grow at 0ºC but prefer to grow in the range of 20ºC - 42ºC • Campylobacter jejuni can grow at low temperatures

50. Oxygen • Aerobes – need a good supply of oxygen. • Microaerophiles – live in areas of low oxygen. • Anaerobes – do not and can not use oxygen. • Aerotolerant – can grow with oxygen present. • Obligate anaerobes are killed by any oxygen. • H2S not H2O • Clostridium species botulism gangrene. • Facultative - grow in the presence or reduced oxygen. • Facultative aerobe prefers anaerobic conditions. • Facultative anaerobe prefers aerobic conditions. • Capnophilic – low oxygen but high CO2 • Streptococcus are capnophilic