Supplemental Lecture (98/03/28 update) by Stephen T. Abedon (

  1. Chapter title: Bacteria Cell Shapes and Arrangements
    1. A list of vocabulary words is found toward the end of this document
    2. Following binary fission, the newly formed bacteria spontaneously assume (or, end up with) a characteristic shape. This shape varies significantly among species of bacteria and may be employed in the course of isolate identification. Two major shape classes are cocci and bacilli though there are many variations on these themes, additional distantly related shapes, as well as many variations on the degree to which cells separate or interact following their division.
  2. Bacteria sizes
    1. Large range in size:
      1. Bacteria range in size from approximately as small as the largest viruses to large enough for single cells to be visible by the naked eye.
      2. That is, from about 0.1 to about 600 Ám over a single dimension.
      3. "Bacteria vary in size as much as in shape. The smallest (e.g., some members of the genus Mycoplasma) are about 100 to 200 nm in diameter, approximately the size of the largest viruses (poxviruses). Escherichia coli, a bacillus of about average size, is 1.1 to 1.5 Ám wide by 2.0 to 6.0 Ám long. A few become fairly large; some spirochetes occasionally reach 500 Ám in length, and the cyanobacterium Oscillatoria is about 7 Ám in diameter (the same diameter as a red blood cell). Recently a huge bacterium has been discovered in the intestine of the brown surgeonfish, Acanthurus nigrofuscus. Epulopiscium fishelsoni grows as large as 600 Ám by 80 Ám, a little smaller than a printed hyphen. It is now clear that a few bacterium are much larger than the average eucaryotic cell." (p. 39-40, Prescott et al., 1996)
    2. Example: a very big bacterium:
      1. Epulopiscium fishelsoni is an example of a very big procaryote.
      2. "Epulopiscium fishelsoni (is) a procaryote related to the gram-positive genus Clostridium. . . Epulopiscium appears to overcome the size limits set by diffusion by having an outer layer consisting of a highly convoluted plasma membrane. . . The bacterium reproduces when between one and about seven daughter cells develop asexually within the parent and then escape through a centrally located slit in the parental cell envelope. . . The discovery of this procaryote greatly weakens the distinction between procaryotes and eucaryotes based on cell size. . ." (p. 41, Prescott et al., 1996)
      3. In stark contrast to the large size of Epulopiscium fishelsoni, there exists an extremely small (i.e., bacteria size) eucaryote, Nanochlorum eukaryotum. "Nanochlorum eukaryotum is only about 1 to 2 Ám in diameter (about the size of E. coli), yet is truly eucaryotic and has a nucleus, a chrloroplast, and a mitochondrion." (p. 41, Prescott et al., 1996)
  3. Surface to volume ratio
    1. "Because of their small size, bacteria have a large surface-to-volume ratio. For example, spherical bacteria with a diameter of 2 Ám have a surface area of about 12 Ám2 and a volume of about 4 Ám3. Their surface-to-volume ratio is 12:4, or 3:1. In contrast, eukaryotic cells with a diamter of 20 Ám have a surface area of about 1200 Ám2 and a volume of about 4000 Ám3. Their surface-to-volume ratio is 1200:4000, or 0.3:1---only one-tenth as great. The large surface-to-volume ratio of bacteria means that no internal part of the cell is very far from the surface and that nutrients can easily and quickly reach all parts of the cell." (p. 75, Black, 1996)
    2. The large surface to volume ratio seen in bacteria is one reason that procaryotes are so successful despite their relatively simple morphologies.
  4. Cocci [sing. Coccus]
    1. Generally spherical:
      1. A bacterial shape.
      2. Generally spherical though with some variation from this theme (i.e., elongation or flattening on one side).
    2. Example: Chlamydia trachomatis
    3. See illustration below.
  5. Diplococci
    1. Cocci that remain in pairs after they divide. See illustration below.
    2. Examples:
      1. Neisseria gonorrhoeae
      2. Neisseria meningitidis
  6. Streptococci
    1. Cocci that fail to separate after they divide, but instead remain in chains of cells.
    2. Examples:
      1. Streptococcus spp.
      2. Enterococcus spp.
      3. Lactococcus spp.
    3. See illustration below.
  7. Tetrad
    1. Cocci that fail to separate after they divide, but instead remain in groups of four forming squares.
    2. Micrococcus luteus
    3. See illustration below.
  8. Sarcinae ('sër-si-ne)
    1. Cocci that fail to separate after they divide, but instead remain in groups of eight forming cubes.
    2. Examples: Sarcina spp.
    3. See illustration below.
  9. Staphylococci
    1. Cocci that fail to separate after they divide, but instead remain in amorphous sheets or clumps.
    2. Examples: Staphylococcus aureus
    3. See illustration below.
  10. Illustration, cocci
  11. Bacilli [sing. Bacillus]
    1. Rods:
      1. Variations on rod-shaped bacteria:
        1. rod
        2. tapered rod
        3. staff
        4. cigar
        5. oval
        6. curved
      2. Basically, bacilli are longer than they are wide and lack extreme curvature.
    2. Bacilli typically divide only across their short axis.
    3. Examples:
      1. Consider rod shaped to be default for a bacterium. That is, if you don't know what shape a bacterium is, your best bet is to just go with rod.
      2. Examples otherwise include:
        1. Bacillus anthracis
        2. Bacillus subtilis
        3. Chlostridium botulinum
        4. Chlostridium perfringens
        5. Chlostridium tetani
        6. Escherichia coli
        7. Haemophilus influenzae
        8. Klebsiella spp.
        9. Lactobacillus spp.
        10. Legionella spp.
        11. Listeria monocytogenes
        12. Mycobacterium leprae
        13. Mycobacterium tuberculosis
        14. Pasteurella pestis
        15. Proteus spp.
        16. Pseudomonas spp.
        17. Salmonella spp.
        18. Serratia marcescens
        19. Shigella spp.
        20. Yersinia pestis
        21. In addition to this list is Vibrio cholerae, which is a curved rod.
    4. See illustration below.
  12. Diplobacilli
    1. Paired rods:
      1. Bacilli that remain in pairs after they divide.
      2. See illustration below.
  13. Streptobacilli
    1. Bacilli that fail to separate after they divide, but instead remain in chains of cells.
    2. Example: Bacillus megaterium
    3. See illustration below.
  14. Coccobacilli
    1. Ambiguous designation:
      1. A short Bacilli that nearly looks like a cocci.
      2. A shape that exists simply to show that bacteria are so diverse that even characterizing them by shape is ambiguous?
    2. Example: Bordetella pertussis
    3. See illustration below.
  15. Illustration, bacilli
  16. Additional bacterial shapes
    1. Additional bacterial shapes include:
      1. Budding Hyphomicrobium spp.
      2. Commas
        1. Bdellovibrio spp.
      3. Corkscrews
      4. Helical
        1. Borrelia burgdorferi
        2. Helicobacter pylori
        3. Treponema pallidum
      5. mycelium (hyphae)
        1. Actinomycetes
        2. Hyphomicrobium spp.
      6. spirillum (rigid, wavy spirals)
      7. spirochetes (flexible spirals)
        1. Borrelia burgdorferi
        2. Treponema pallidum
      8. squares
      9. stars
      10. etc.
    2. See, for example, the illustration of a spirochete below.
  17. Illustration, spirochete
  18. Monomorphic
    1. A trait of a bacterium that tends to display the same shape regardless of physiological or environmental conditions.
  19. Pleomorphic [polymorphic, pleiomorphic]
    1. A trait of a bacterium that can display different shapes under different physiological or environmental conditions, or even in the same culture.
    2. Examples:
      1. Corynebacterium diphtheriae
      2. Mycoplasma pneumoniae
      3. Rickettsia prowazekii
      4. Rickettsia rickettsiia
    3. Note that both Corynebacterium diphtheriae is a pleimorphic rod.
  20. Vocabulary
    1. Bacilli
    2. Bacilli, illustration
    3. Bacillus
    4. Additional bacterial shapes
    5. Cocci
    6. Cocci, illustration
    7. Coccobacilli
    8. Coccus
    9. Diplobacilli
    10. Diplococci
    11. Monomorphic
    12. Pleomorphic
    13. Polymorphic
    14. Sarcinae
    15. Spirochete, illustration
    16. Staphylococci
    17. Streptobacilli
    18. Streptococci
    19. Surface to volume ratio
    20. Tetrad
  21. Practice questions
    1. Draw in outline and label (i) streptobacilli, (ii) diplococci, and (iii) staphylococci (make sure I can tell the difference between your cocci and bacilli). [PEEK]
    2. You observe a culture of predominantly round (presumably spherical) bacteria that though apparently fully divided, nevertheless have failed to separate, thus resulting in long chains of cells. What, generally, might you call such an arrangement? [PEEK]
    3. Which of the following normally occurs as only individual, spherical cells? (circle best answer) [PEEK]
      1. Chlamydia trachomatis.
      2. Escherichia coli.
      3. Bacillus subtilis.
      4. Clostridium tetani.
      5. Helicobacter pylori.
      6. Treponema pallidum.
    4. In terms of planes of division, describe why Micrococcus luteus forms tetrads rather than streptococci.[PEEK]
    5. Circle all of the spiral or helical-shaped bacteria. [PEEK]
      1. Bacillus anthracis, Bacillus subtilis, Bdellovibrio spp., Bordetella pertussis, Borrelia burgdorferi, Chlamydia trachomatis, Clostridium botulinum, Clostridium perfringens, Clostridium tetani, Corynebacterium diphtheriae, Escherichia coli, Helicobacter pylori, Hemophilus influenzae, Klebsiella spp., Lactobacillus spp., Legionella spp., Listeria monocytogenes, Mycobacterium leprae, Mycobacterium tuberculosis, Mycoplasma pneumoniae, Neisseria gonorrhoeae, Neisseria meningitidis, Pasteurella pestis, Proteus spp., Pseudomonas spp., Rickettsia prowazekii, Rickettsia rickettsii, Salmonella spp., Serratia marcescens, Shigella spp., Staphylococcus aureus, Streptococcus spp., Treponema pallidum, Vibrio cholerae, Yersinia pestis
    6. Name one pleomorphic bacterium. [PEEK]
    7. Cells are generally small because __________. (circle best answer) [PEEK]
      1. this assures that they can fit in small places.
      2. this assures that their plasma membrane is sufficiently large.
      3. this assures that their nucleus remains in contact with their cytoplasm.
      4. phospholipids are expensive to make so are used sparingly.
      5. all of the above.
      6. none of the above.
    8. What is the shape of Bdellovibrio spp. [PEEK]
    9. Shape and arrangement in which Neisseria meningitidis is normally found. [PEEK]
    10. Describe the shape and arrangement of the cells of Neisseria gonorrhoeae. [PEEK]
    11. Distinguish Listeria monocytogenes and Vibrio cholerae in terms of cell shape. [PEEK]
    12. Vibrio cholera? [PEEK]
    13. Treponema pallidum? [PEEK]
    14. The shape and arrangement of __________ is diplococci. [PEEK]
      1. Escherichia coli
      2. Micrococcus luteus
      3. Neisseria Meningitidis
      4. Mycobacterium tuberculosis
      5. Mycoplasma pneumoniae
      6. Mycobacterium smegmatis
    15. What is the arrangement of Micrococcus luteus? [PEEK]
  22. Practice question answers
    1. A streptobacillusstreptobacilli is found in a chain of cells which are connected at the polar ends, not on the broad sides. A diplococcusdiplococci is found as one of a pair of circular (actually spherical) cells bound together. A staphylococcusstaphylococci is a circular cell found in a sheet or clump of such cells.
    2. Streptococci
    3. i, Chlamydia trachomatis.
    4. Tetrads form when division occurs in two alternating and perpendicular planes, while streptococci form as a consequence of division consistently in only a single plane (i.e. on perpendicular to the central axis of the chain).
    5. Borrelia burgdorferi, Helicobacter pylori, Treponema pallidum.
    6. Corynebacterium diphtheriae, Mycoplasma pneumoniae, Rickettsia prowazekii, Rickettsia rickettsii.
    7. ii, this assures that their plasma membrane is sufficiently large. This is another way of saying that having a large surfact to volume ratio is often advantageous to a cell.
    8. partially helical, comma shaped, non-spirochete; bacilli is a very weak answer which I would consider unacceptable given the publication of this statement (i.e., if you are reading this from your lecture notes copy, don't use it).
    9. Diplococci
    10. Diplococci
    11. Vibrio cholerae is a curved rod while Listeria monocytogenes is simply a rod.
    12. <spirochete/flexible spiral/helical
    13. Neisseria gonorrhoeae, Neisseria meningitidis
    14. Tetrad
  23. References
    1. Black, J.G. (1996). Microbiology. Principles and Applications. Third Edition. Prentice Hall. Upper Saddle River, New Jersey. pp. 75-78.
    2. Prescott, L.M., Harley, J.P., Klein, D.A. (1996). Microbiology. Third Edition. Wm. C. Brown Publishers, Dubuque, IA. pp. 37-41.
    3. Tortora, G.J., Funke, B.R., Case, C.L. (1995). Microbiology. An Introduction. Fifth Edition. The Benjamin/Cummings Publishing, Co., Inc., Redwood City, CA, pp. 71, 72-73.