1. Chapter 7 Topics Microbial Nutrition Environmental Factors
Microbial Growth

2. Microbial Nutrition Chemical analysis Sources of essential nutrients
Transport mechanisms

3. Bacteria are composed of different elements and molecules, with water (70%) and proteins (15%) being the most abundant.
Table 7.2 Analysis of the chemical composition
of an E. coli cell.

4. Sources of essential nutrients
Required for metabolism and growth
Carbon source
Energy source

5. Carbon source Heterotroph (depends on other life forms)
Organic molecules
Ex. Sugars, proteins, lipids
Autotroph (self-feeders)
Inorganic molecules
Ex. CO2

6. Growth factors Essential organic nutrients
Not synthesized by the microbe, and must be supplemented
Ex. Amino acids, vitamins

7. Energy source
Chemoheterotrophs
Photoautotrophs
Chemoautotrophs

8. Chemoheterotrophs Derive both carbon and energy from organic compounds
Saprobic
decomposers of plant litter, animal matter, and dead microbes
Parasitic
Live in or on the body of a host

9. Photoautotroph Derive their energy from sunlight
Transform light rays into chemical energy
Primary producers of organic matter for heterotrophs
Primary producers of oxygen
Ex. Algae, plants, some bacteria

10. Chemoorganic autotrophs
Two types
Chemoorganic autotroph
Derives their energy from organic compounds and their carbon source from inorganic compounds
Lithoautotrophs
Neither sunlight nor organics used, rather it relies totally on inorganics

11. Methanogens are an example of a chemoautotroph.
Fig. 7.1 Methane-producing archaea

12. Representation of a saprobe and its mode of action.
Fig. 7.2 Extracellular digestion in a saprobe with a cell wall.

13. Summary of the different nutritional categories based on carbon and energy source.
Table 7.3 Nutritional categories of microbes by energy
and carbon source.

14. Transport mechanisms
Osmosis
Diffusion
Active transport
Endocytosis

15. Osmosis Diffusion of water through a permeable but selective membrane
Water moves toward the higher solute concentrated areas
Isotonic
Hypotonic
Hypertonic

16. Representation of the osmosis process.
Fig. 7.3 Osmosis, the diffusion of water through a selectively
permeable membrane

17. Cells with- and without cell walls, and their responses to different osmotic conditions (isotonic, hypotonic, hypertonic).
Fig. 7.4 Cell responses to solutions of differing osmotic content.

18. Diffusion
Net movement of molecules from a high concentrated area to a low concentrated area
No energy is expended (passive)
Concentration gradient and permeability affect movement

19. A cube of sugar will diffuse from a concentrated area into a more dilute region, until an equilibrium is reached.
Fig. 7.5 Diffusion of molecules in aqueous solutions

20. Facilitated diffusion
Transport of polar molecules and ions across the membrane
No energy is expended (passive)
Carrier protein facilitates the binding and transport
Specificity
Saturation
Competition

21. Representation of the facilitated diffusion process.
Fig. 7.6 Facilitated diffusion

22. Active transport Transport of molecules against a gradient
Requires energy (active)
Ex. Permeases and protein pumps transport sugars, amino acids, organic acids, phosphates and metal ions.
Ex. Group translocation transports and modifies specific sugars

23. Endocytosis
Substances are taken, but are not transported through the membrane.
Requires energy (active)
Common for eucaryotes
Ex. Phagocytosis, pinocytosis

24. Example of the permease, group translocation, and endocytosis processes.
Fig. 7.7 Active transport

25. Summary of the transport processes in cells.
Table 7.4 Summary of transport processes in cells

26. Environmental Factors
Temperature
Gas pH
Osmotic pressure
Other factors
Microbial association

27. Temperature For optimal growth and metabolism
Psychrophile – 0 to 15 °C
Mesophile- 20 to 40 °C
Thermophile- 45 to 80 °C

28. Growth and metabolism of different ecological groups based on ideal temperatures.
Fig. 7.8 Ecological groups by temperature

29. Example of a psychrophilic photosynthetic Red snow organism.
Fig. 7.9 Red snow

30. Gas Two gases that most influence microbial growth Oxygen
Respiration
Oxidizing agent
Carbon dioxide

31. Oxidizing agent Oxygen metabolites are toxic
These toxic metabolites must be neutralized for growth
Three categories of bacteria
Obligate aerobe
Facultative anaerobe
Obligate anaerobe

32. Obligate aerobe Requires oxygen for metabolism
Possess enzymes that can neutralize the toxic oxygen metabolites
Superoxide dismutase and catalase
Ex. Most fungi, protozoa, and bacteria

33. Facultative anaerobe
Does not require oxygen for metabolism, but can grow in its presence
During minus oxygen states, anaerobic respiration or fermentation occurs
Possess superoxide dismutase and catalase
Ex. Gram negative pathogens

34. Obligate anaerobes Cannot use oxygen for metabolism
Do not possess superoxide dismutase and catalase
The presence of oxygen is toxic to the cell

35. Anaerobes must grow in an oxygen minus environment, because toxic oxygen metabolites cannot be neutralized.
Fig Culturing technique for anaerobes

36. Thioglycollate broth enables the identification of aerobes, facultative anaerobes, and obligate anaerobes.
Fig Use of thioglycollate broth to demonstrate
oxygen requirements.

37. pH Cells grow best between pH 6-8
Exceptions would be acidophiles (pH 0), and alkalinophiles (pH 10).

38. Osmotic pressure Halophiles Requires high salt concentrations
Withstands hypertonic conditions
Ex. Halobacterium
Facultative halophiles
Can survive high salt conditions but is not required
Ex. Staphylococcus aureus

39. Other factors Radiation- withstand UV, infrared
Barophiles – withstand high pressures
Spores and cysts- can survive dry habitats

40. Ecological association
Influence microorganisms have on other microbes
Symbiotic relationship
Non-symbiotic relationship

41. Symbiotic Organisms that live in close nutritional relationship Types
Mutualism – both organism benefit
Commensalism – one organisms benefits
Parasitism – host/microbe relationship

42. An example of commensalism, where Staphylococcus aureus provides vitamins and amino acids to Haemophilus influenzae.
Fig Satellitism, a type of commensalism

43. Non-symbiotic
Organisms are free-living, and do not rely on each other for survival
Types
Synergism – shared metabolism, not required
Antagonism- competition between microorganisms

44. Interrelationships between microbes and humans
Can be commensal, parasitic, and synergistic
Ex. E. coli produce vitamin K for the host

45. Microbial Growth Binary fission Generation time Growth curve
Enumeration of bacteria

46. Binary fission The division of a bacterial cell
Parental cell enlarges and duplicates its DNA
Septum formation divides the cell into two separate chambers
Complete division results in two identical cells

47. Representation of the steps in binary fission of a rod-shaped bacterium.
Fig Steps in binary fission of a rod-shaped bacterium.

48. Generation time
The time required for a complete division cycle (doubling)
Length of the generation time is a measure of the growth rate
Exponentials are used to define the numbers of bacteria after growth

49. Representation of how a single bacterium doubles after a complete division, and how this can be plotted using exponentials.
Fig The mathematics of population growth

50. Growth curve
Lag phase
Log phase
Stationary phase
Death phase

51. Lag phase
Cells are adjusting, enlarging, and synthesizing critical proteins and metabolites
Not doubling at their maximum growth rate

52. Log phase Maximum exponential growth rate of cell division
Adequate nutrients
Favorable environment

53. Stationary phase
Survival mode – depletion in nutrients, released waste can inhibit growth
When the number of cells that stop dividing equal the number of cells that continue to divide

54. Death phase
A majority of cells begin to die exponentially due to lack of nutrients
A chemostat will provide a continuous supply of nutrients, thereby the death phase is never achieved.

55. The four main phases of growth in a bacterial culture.
Fig The growth curve in a bacterial culture.

56. Enumeration of bacteria
Turbidity
Direct cell count
Automated devices
Coulter counter
Flow cytometer
Real-time PCR

57. The greater the turbidity, the larger the population size.
Fig Turbidity measurements as indicators of growth

58. The direct cell method counts the total dead and live cells in a special microscopic slide containing a premeasured grid.
Fig Direct microscopic count of bacteria.

59. A Coulter counter uses an electronic sensor to detect and count the number of cells.
Fig Coulter counter