1. Microbial Growth Increase in number of cells, not cell size
Populations
Colonies

2. The Requirements for Growth
Physical requirements
Temperature pH
Osmotic pressure
Chemical requirements
Carbon
Nitrogen, sulfur, and phosphorous
Trace elements
Oxygen
Organic growth factor

3. Psychrotrophs
Grow between 0°C and 20–30°C
Cause food spoilage

4. Figure 6.2 Food preservation temperatures.
Temperatures in this range destroy most microbes,
although lower temperatures take more time.
Very slow bacterial growth.
Rapid growth of bacteria; some may produce toxins.
Danger zone
Many bacteria survive; some may grow.
Refrigerator temperatures; may allow slow growth
of spoilage bacteria, very few pathogens.
No significant growth below freezing.

5. pH Most bacteria grow between pH 6.5 and 7.5
Molds and yeasts grow between pH 5 and 6
Acidophiles grow in acidic environments

6. Osmotic Pressure
Hypertonic environments, or an increase in salt or sugar, cause plasmolysis
Extreme or obligate halophiles require high osmotic pressure
Facultative halophiles tolerate high osmotic pressure

7. Cell in isotonic solution. Plasmolyzed cell in hypertonic solution.
Figure 6.4 Plasmolysis.
Plasma
membrane
Plasma
membrane
Cell wall
H2O
Cytoplasm
Cytoplasm
NaCl 0.85%
NaCl 10%
Cell in isotonic solution.
Plasmolyzed cell in hypertonic solution.

8. Chemical Requirements
Carbon
Structural organic molecules, energy source
Chemoheterotrophs use organic carbon sources
Autotrophs use CO2

9. Chemical Requirements
Nitrogen
In amino acids and proteins
Most bacteria decompose proteins
Some bacteria use NH4+ or NO3–
A few bacteria use N2 in nitrogen fixation

10. Chemical Requirements
Sulfur
In amino acids, thiamine, and biotin
Most bacteria decompose proteins
Some bacteria use SO42– or H2S
Phosphorus
In DNA, RNA, ATP, and membranes
PO43– is a source of phosphorus

11. Chemical Requirements
Trace elements
Inorganic elements required in small amounts
Usually as enzyme cofactors

12. Table 6.1 The Effect of Oxygen on the Growth of Various Types of Bacteria

13. Organic Growth Factors
Organic compounds obtained from the environment
Vitamins, amino acids, purines, and pyrimidines

14. Biofilms Microbial communities Form slime or hydrogels
Bacteria attracted by chemicals via quorum sensing

15. Clumps of bacteria adhering to surface Migrating clump of bacteria
Figure 6.5 Biofilms.
Clumps of bacteria adhering to surface
Migrating clump of bacteria
Surface
Water currents

16. Biofilms
Share nutrients
Sheltered from harmful factors

17. Applications of Microbiology 3.2 Pseudomonas aeruginosa biofilm.
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18. Biofilms
Patients with indwelling catheters received contaminated heparin
Bacterial numbers in contaminated heparin were too low to cause infection
84–421 days after exposure, patients developed infections

19. Culture Media Culture medium: nutrients prepared for microbial growth
Sterile: no living microbes
Inoculum: introduction of microbes into medium
Culture: microbes growing in/on culture medium

20. Agar Complex polysaccharide
Used as solidifying agent for culture media in Petri plates, slants, and deeps
Generally not metabolized by microbes
Liquefies at 100°C
Solidifies at ~40°C

21. Culture Media
Chemically defined media: exact chemical composition is known
Complex media: extracts and digests of yeasts, meat, or plants
Nutrient broth
Nutrient agar

22. Table 6.2 A Chemically Defined Medium for Growing a Typical Chemoheterotroph, Such as Escherichia coli

23. Table 6.3 Defined Culture Medium for Leuconostoc mesenteroides

24. Table 6.4 Composition of Nutrient Agar, a Complex Medium for the Growth of Heterotrophic Bacteria

25. Anaerobic Culture Methods
Reducing media
Contain chemicals (thioglycolate or oxyrase) that combine O2
Heated to drive off O2

26. Envelope containing sodium bicarbonate and sodium borohydride
Figure 6.6 A jar for cultivating anaerobic bacteria on Petri plates.
Clamp with clamp screw
Lid with
O-ring gasket
Envelope containing sodium bicarbonate and sodium borohydride
Palladium catalyst pellets
Anaerobic indicator (methylene blue)
Petri plates

27. Figure 6.7 An anaerobic chamber.
Air lock
Arm ports

28. Capnophiles Microbes that require high CO2 conditions CO2 packet
Candle jar

29. Biosafety Levels BSL-1: no special precautions
BSL-2: lab coat, gloves, eye protection
BSL-3: biosafety cabinets to prevent airborne transmission
BSL-4: sealed, negative pressure
Exhaust air is filtered twice

30. Figure 6.8 Technicians in a biosafety level 4 (BSL-4) laboratory.

31. Differential Media
Make it easy to distinguish colonies of different microbes

32. Bacterial colonies Hemolysis
Figure 6.9 Blood agar, a differential medium containing red blood cells.
Bacterial colonies
Hemolysis

33. Selective Media
Suppress unwanted microbes and encourage desired microbes

34. Uninoculated Staphylococcus epidermis Staphylococcus aureus
Figure 6.10 Differential medium.
Uninoculated
Staphylococcus
epidermis
Staphylococcus
aureus

35. Enrichment Culture Encourages growth of desired microbe
Assume a soil sample contains a few phenol-degrading bacteria and thousands of other bacteria
Inoculate phenol-containing culture medium with the soil, and incubate
Transfer 1 ml to another flask of the phenol medium, and incubate
Only phenol-metabolizing bacteria will be growing

36. Obtaining Pure Cultures
A pure culture contains only one species or strain
A colony is a population of cells arising from a single cell or spore or from a group of attached cells
A colony is often called a colony-forming unit (CFU)
The streak plate method is used to isolate pure cultures

37. Figure 6.11 The streak plate method for isolating pure bacterial cultures.2 3
Colonies

38. Preserving Bacterial Cultures
Deep-freezing: –50° to –95°C
Lyophilization (freeze-drying): frozen (–54° to –72°C) and dehydrated in a vacuum

39. Reproduction in Prokaryotes
Binary fission
Budding
Conidiospores (actinomycetes)
Fragmentation of filaments

40. (a) A diagram of the sequence of cell division
Figure 6.12a Binary fission in bacteria.
Cell wall
Cell elongates and DNA is replicated.
Plasma membrane
Cell wall and plasma membrane begin to constrict.
DNA (nucleoid)
Cross-wall forms, completely separating the two DNA copies.
Cells separate.
(a) A diagram of the sequence of cell division

41. Partially formed cross-wall
Figure 6.12b Binary fission in bacteria.
Partially formed cross-wall
DNA (nucleoid)
Cell wall
(b) A thin section of a cell of Bacillus licheniformis starting to divide
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42. Figure 6.13a Cell division.

43. Figure 6.15 Understanding the Bacterial Growth Curve.
Lag Phase
Intense activity preparing for population growth, but no increase in population.
Log Phase
Logarithmic, or exponential, increase in population.
Stationary Phase
Period of equilibrium; microbial deaths balance production of new cells.
Death Phase
Population Is decreasing at a logarithmic rate.
The logarithmic growth in the log phase is due to reproduction by binary fission (bacteria) or mitosis (yeast).
Staphylococcus spp.

44. Measuring Microbial Growth
Direct Methods
Plate counts
Filtration
MPN
Direct microscopic count
Indirect Methods
Turbidity
Metabolic activity
Dry weight