1. Microbial Growth
Microbial growth = increase in number of cells, not cell size

2. The Requirements for Growth: Physical Requirements
Temperature
Minimum growth temperature
Optimum growth temperature
Maximum growth temperature

3. Temperature
Figure 6.1

4. Psychrotrophs
Grow between 0°C and 20-30°C
Cause food spoilage

5. Psychrotrophs
Figure 6.2

6. Temperature Mesophiles (moderate temp. loving microbes)
range °C °C
Thermophiles (heat loving microbes)
range °C °C

7. The Requirements for Growth: Physical Requirements
Most bacteria grow between pH 6.5 and 7.5
Molds and yeasts grow between pH 5 and 6
Acidophiles grow in acidic environments

8. The Requirements for Growth: Physical Requirements
Osmotic Pressure
Hypertonic environments, increase salt or sugar, cause plasmolysis
Extreme or obligate halophiles require high osmotic pressure
Facultative halophiles tolerate high osmotic pressure

9. The Requirements for Growth: Physical Requirements
Figure 6.4

10. The Requirements for Growth: Chemical Requirements
Carbon
Structural organic molecules, energy source
Chemoheterotrophs use organic carbon sources
Autotrophs use CO2

11. The Requirements for Growth: Chemical Requirements
Nitrogen
In amino acids, proteins
Most bacteria decompose proteins
Some bacteria use NH4+ or NO3
A few bacteria use N2 in nitrogen fixation
Sulfur
In amino acids, thiamine, biotin
Some bacteria use SO42 or H2S
Phosphorus
In DNA, RNA, ATP, and membranes
PO43 is a source of phosphorus

12. The Requirements for Growth: Chemical Requirements
Trace Elements
Inorganic elements required in small amounts
Usually as enzyme cofactors

13. The Requirements for Growth: Chemical Requirements
Oxygen (O2)

14. Toxic Forms of Oxygen
Singlet oxygen(1O2- ): boosted to a higher-energy state
Superoxide free radicals: O2
Peroxide anion: O22
Hydroxyl radical (OH)

15. The Requirements for Growth: Chemical Requirements
Organic Growth Factors
Organic compounds obtained from the environment
Vitamins, amino acids, purines, pyrimidines

16. Culture Media Culture Medium: Nutrients prepared for microbial growth
Inoculum: Introduction of microbes into medium
Culture: Microbes growing in/on culture medium

17. Criteria a culture media must meet
Contain right nutrients for the growth of microorganisms we want to grow
Proper moisture, pH, O2 level etc.
It must be sterile – its must initially contain no other organisms
The culture should be incubated in proper temperature

18. 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 ~40°C

19. Culture Media
Chemically Defined Media: Exact chemical composition is known
Complex Media: Extracts and digests of yeasts, meat, or plants
Nutrient broth
Nutrient agar

20. Culture Media
Table 6.2 & 6.4

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

22. Anaerobic Culture Methods
Anaerobic jar
Figure 6.5

23. Anaerobic Culture Methods
Anaerobic chamber
Figure 6.6

24. Capnophiles require high CO2
Candle jar
CO2-packet
Figure 6.7

25. Selective Media
designed to suppress the growth of unwanted bacteria and encourage the growth of the desired microbes
Bismuth sulfite agar is one medium used to isolate the typhoid bacterium, the gram-negative Salmonella typhi from feces.
Bismuth sulfite inhibits gram positive bacteria and most gram-negative intestinal bacteria (other than S. typhi), as well.
Sabouraud's dextrose agar, which has a pH of 5.6, is used to isolate fungi that outgrow most bacteria at this pH.

26. Differential Media
Make it easy to distinguish colonies of different microbes.
Figure 6.9a

27. Enrichment Media 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

28. 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)

29. Streak Plate
Figure 6.10a, b

30. Preserving Bacteria Cultures
Deep-freezing: -50°to -95°C
Lyophilization (freeze-drying): Frozen (-54° to -72°C) and dehydrated in a vacuum

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

32. Binary Fission
Figure 6.11

33. Figure 6.12b

34. If 100 cells growing for 5 hours produced 1,720,320 cells:

35. Figure 6.13

36. Figure 6.14

37. Lag phase
The number of cells changes very little because the cells do not immediately reproduce in a new medium
Little or no cell division
It can last for 1 hour or several days
The cells are not dormant
The microbial population is undergoing a period of intense metabolic activity involving, in particular, synthesis of enzymes and various molecules.

38. Log Phase
The cells begin to divide and enter a period of growth, or logarithmic increase
Also called exponential growth phase
Cellular reproduction is most active during this period
Generation time reaches a constant minimum.
A logarithmic plot of growth during the log phase is a straight line.
The log phase is the time when cells are most active metabolically and is preferred for industrial purposes

39. Stationary Phase
If exponential growth continues unchecked, startlingly large numbers of cells could arise
A single bacterium (at a weight of 9.5 X g per cell) dividing every 20 minutes for only 25.5 hours can theoretically produce a population equivalent in weight to that of an 80,000-ton aircraft carrier.
In reality, this does not happen
Eventually, the growth rate slows, the number of microbial deaths balances the number of new cells, and the population stabilizes
This period of equilibrium is called the stationary phase.
The exhaustion of nutrients, accumulation of waste products, and harmful changes in pH may all play a role.

40. Death Phase
The number of deaths eventually exceeds the number of new cells formed
The population enters the death phase, or logarithmic decline phase
Phase continues until the population is diminished to a tiny fraction of the number of cells in the previous phase or until the population dies out entirely

41. Direct Measurements of Microbial Growth
Plate Counts: Perform serial dilutions of a sample
Figure 6.15, top portion

42. Plate Count
Inoculate Petri plates from serial dilutions
Figure 6.16

43. Plate Count
After incubation, count colonies on plates that have colonies (CFUs)
Figure 6.15

44. Direct Measurements of Microbial Growth
Filtration
Figure 6.17a, b

45. Direct Measurements of Microbial Growth
Direct Microscopic Count

46. Direct Measurements of Microbial Growth
Figure 6.19

47. Estimating Bacterial Numbers by Indirect Methods
Turbidity
Figure 620

48. Estimating Bacterial Numbers by Indirect methods
Metabolic activity
Dry weight