1. Introduction to Microbiology Lecture 5
“Small creatures, big impacts”
Lecture 5

2. Introduction to Microbiology
Lecture outline
Cell membranes, Spores, Motility
Microbial reproduction- cell division and growth curves
Bacterial conjugation and horizontal gene transfer
Introduction to Microbiology

3. Cell membranes, spores, motility

4. Cytoplasmic (cell) membrane
Thin structure that surrounds the cell
6–8 nm thick
Vital barrier that separates cytoplasm from environment
Highly selective permeable barrier; enables concentration of specific metabolites and excretion of waste products
Cell membranes, spores, motility

5. Cytoplasmic (cell) membrane
Phospholipid bilayer
Hydrophobic and hydrophilic components
Cell membranes, spores, motility

6. Cytoplasmic (cell) membrane
Embedded proteins
Mg2+ and Ca2+ stabilize (ionic bonds)
Somewhat fluid
Cell membranes, spores, motility

7. Cytoplasmic (cell) membrane
Membrane-Strengthening Agents
Sterols
Rigid, planar lipids found in eukaryotic membranes
Strengthen and stabilize membranes
Hopanoids
Structurally similar to sterols
Present in membranes of many Bacteria
Cell membranes, spores, motility

8. Cytoplasmic (cell) membrane
Cell membranes, spores, motility
Sterol (Cholesterol)
Hopanoid (diploptene)

9. Cytoplasmic (cell) membrane
Archaeal Membranes
Ether linkages in phospholipids
Bacteria and Eukarya: ester linkages
Archaeal lipids: isoprenes instead of fatty acids
Major lipids are glycerol diethers
Can exist as lipid monolayers instead of bilayers
Cell membranes, spores, motility

10. Cytoplasmic (cell) membrane
Cell membranes, spores, motility
Ester linkage
Ether linkage
Isoprene

11. Cytoplasmic (cell) membrane
Cell membranes, spores, motility

12. Cytoplasmic (cell) membrane
Cell membranes, spores, motility

13. Cell membranes, spores, motility
Cytoplasmic membrane: major functions
Cell membranes, spores, motility

14. Cell membranes, spores, motility
Cell wall
Provides support to cell
Present in most Bacteria and Archaea
Peptidoglycan in Bacteria
Rigid layer that provides strength to cell wall
Polysaccharide composed of
N-acetylglucosamine and N-acetylmuramic acid
Amino acids
Cell membranes, spores, motility

15. Cell membranes, spores, motility

16. Cell membranes, spores, motility
wall
Peptidoglycan
layer
Plasma membrane
Protein
(a) Gram-positive: peptidoglycan traps
crystal violet.
Cell membranes, spores, motility

17. Cell membranes, spores, motility
wall
Peptidoglycan
layer
Plasma membrane
Protein
(b) Gram-negative: crystal violet is easily rinsed
away, revealing red dye.
Outer
membrane
Carbohydrate portion
of lipopolysaccharide
Cell membranes, spores, motility

18. Cell membranes, spores, motility
Cell wall in Archaea
No peptidoglycan
Typically no outer membrane
Some have Pseudomurein
Polysaccharide similar to peptidoglycan
Composed of N-acetylglucosamine and N-acetylalosaminuronic acid
Other Archaea: Polysaccharide, glycoprotein or protein walls
Cell membranes, spores, motility

19. Cell membranes, spores, motility

20. Attachment: Fibriae or Pilli
Fimbriae
200 nm
Cell membranes, spores, motility

21. Cell membranes, spores, motility
Motility: Flagella
Flagellum
Filament
Hook
Basal apparatus
Cell wall
Plasma
membrane
50 nm
Cell membranes, spores, motility

22. Cell membranes, spores, motility
Motility: Flagella
Cell membranes, spores, motility

23. Cell membranes, spores, motility
Chemotaxis
Cell membranes, spores, motility

24. Cell membranes, spores, motility
Endospores
Highly differentiated cells resistant to heat, harsh chemicals, and radiation
“Dormant” stage of bacterial life cycle
Ideal for dispersal via wind, water, or animal gut
Only present in some gram-positive bacteria
Cell membranes, spores, motility

25. Cell membranes, spores, motility
Endospores
Cell membranes, spores, motility

26. Cell membranes, spores, motility
Endospore survival
Extremely long survival:
25-40 million years: Bacillus endospores trapped in the gut of an extinct bee preserved in amber
> 250 million years: Halophile endospores trapped in salt crystals
Cell membranes, spores, motility

27. Endospore survival: space travel?
Life could have been delivered to Earth as part of a meteorite
Bacillus spores can survive:
Extreme acceleration
Strong heating
Survive radiation and dessication in deep space for nearly 6 years!
Survive extreme pressure in simulated meteorite impacts
Cell membranes, spores, motility

28. Prokaryote reproduction & conjugation

29. Bacterial fission: every 1-3 hours
Microbial reproduction & conjugation

30. Considerable genetic variation
Three factors:
Rapid reproduction
Mutation
Genetic recombination
Mutation rates: extremely low, e.g. 1 in 10 million cell divisions
Rapid reproduction: e.g. 2 X 1010 new E. coli cells in human intestines per day
Number of mutations per gene per day
= (2X1010) (1X10-7) = 2000
Microbial reproduction & conjugation

31. Genetic recombination
Three processes:
transformation, transduction, and conjugation
Important for Horizontal gene transfer
Transformation: take up and incorporate foreign DNA from the environment
Transduction: movement of genes between bacteria by bacteriophages
Microbial reproduction & conjugation

32. Microbial reproduction & conjugation
Recombinant cell
Recipient
cell A+ B– A–
Recombination
Donor B+
Phage DNA
Microbial reproduction & conjugation

33. Microbial reproduction & conjugation
Conjugation: genetic material is transferred between bacterial cells
Sex pili allow cells to connect and pull together for DNA transfer
F factor: Piece of DNA required for production of sex pili
separate plasmid
DNA within the bacterial chromosome
Microbial reproduction & conjugation

34. Microbial reproduction & conjugation
Sex pilus
1 µm
Microbial reproduction & conjugation

35. Microbial reproduction & conjugation
F Factor as plasmid:
Cells containing F plasmid: DNA donors
Cells without F factor: DNA recipients
F factor transferable during conjugation
Microbial reproduction & conjugation

36. Microbial reproduction & conjugation
F Factor in chromosome:
Cell with F factor built into chromosome: donor
Recipient becomes recombinant bacterium, with DNA from two different cells
HFR= High Frequency of Recombination
Microbial reproduction & conjugation
F factor
Hfr cell
(b) Conjugation and transfer of part of an Hfr bacterial chromosome A+ A–
F– cell
Recombinant
F– bacterium

37. Microbial reproduction & conjugation
Gene transfer
R plasmids: antibiotic resistance
R plasmids carry genes for antibiotic resistance
Antibiotics select for bacteria with genes that are resistant to the antibiotics
Antibiotic resistant strains of bacteria are becoming more common
Microbial reproduction & conjugation