1. Microbiology: A Systems Approach, 2nd ed.
Chapter 7: Microbial Nutrition, Ecology, and Growth

2. 7.1 Microbial Nutrition
Nutrition: a process by which chemical substances (nutrients) are acquired from the environment and used in cellular activities
All living things require a source of elements such as C, H, O, P, K, N, S, Ca, Fe, Na, Cl, Mg- but the relative amounts vary depending on the microbe
Essential Nutrient: any substances that must be provided to an organism
Macronutrients: Required in relatively large quantities, play principal roles in cell structure and metabolism (ex. C, H, O)
Micronutrients: aka trace elements, present in smaller amounts and involved in enzyme function and maintenance of protein structure (ex. Mn, Zn, Ni)
Nutrients are processed and transformed into the chemicals of the cell after absorption
Can also categorize nutrients according to C content
Inorganic nutrients: A combination of atoms other than C and H
Organic nutrients: Contain C and H, usually the products of living things

4. Chemical Analysis of Microbial Cytoplasm

5. Sources of Essential Nutrients
Carbon sources
Nitrogen sources
Oxygen sources
Hydrogen sources
Phosphorus sources
Sulfur sources
Others

6. Carbon Sources
The majority of C compounds involved in normal structure and metabolism of all cells are organic
Heterotroph: Must obtain C in organic form (nutritionally dependent on other living things)
Autotroph: Uses inorganic CO2 as its carbon source (not nutritionally dependent on other living things)

7. Nitrogen Sources Main reservoir- N2
Primary nitrogen source for heterotrophs- proteins, DNA, RNA
Some bacteria and algae utilize inorganic nitrogenous nutrients
Small number can transform N2 into usable compounds through nitrogen fixation
Regardless of the initial form, must be converted to NH3 (the only form that can be directly combined with C to synthesize amino acids and other compounds)

8. Oxygen Sources O is a major component of organic compounds
Also a common component of inorganic salts
O2 makes up 20% of the atmosphere

9. Hydrogen Sources
H is a major element in all organic and several inorganic compounds
Performs overlapping roles in the biochemistry of cells:
Maintaining pH
Forming hydrogen bonds between molecules
Serving as the source of free energy in oxidation-reduction reactions of respiration

10. Phosphorus (Phosphate) Sources
Main inorganic source of phosphorus is phosphate (PO43-)
Derived from phosphoric acid
Found in rocks and oceanic mineral deposits
Key component in nucleic acids
Also found in ATP
Phospholipids in cell membranes and coenzymes

11. Sulfur Sources
Widely distributed throughout the environment in mineral form
Essential component of some vitamins
Amino acids- methionine and cysteine

12. Other Nutrients Important in microbial Metabolism
Potassium- protein synthesis and membrane function
Sodium- certain types of cell transport
Calcium- stabilizer of cell walls and endospores
Magnesium- component of chlorophyll and stabilizer of membranes and ribosomes
Iron- important component of cytochrome proteins
Zinc- essential regulatory element for eukaryotic genetics, and binding factors for enzymes
Cooper, cobalt, nickel, molybdenum, manganese, silicon, iodine, and boron- needed in small amounts by some microbes but not others

13. Growth Factors: Essential Organic Nutrients
Growth factor: An organic compound such as an amino acid, nitrogenous base, or vitamin that cannot be synthesized by an organism and must be provided as a nutrient
For example, many cells cannot synthesize all 20 amino acids so they must obtain them from food (essential amino acids)

14. How Microbes Feed: Nutritional Types

15. Main Determinants of Nutritional Type
Sources of carbon and energy
Phototrophs- Microbes that photosynthesize
Chemotrophs- Microbes that gain energy from chemical compounds

16. Autotrophs and Their Energy Sources
Photoautotrophs
Photosynthetic
Form the basis for most food webs
Chemoautotrophs
Chemoorganic autotrophs- use organic compounds for energy and inorganic compounds as a carbon source
Lithoautotrophs- rely totally on inorganic minerals
Methanogens- produce methane from hydrogen gas and carbon dioxide
Archae
Some live in extreme habitats

17. Figure 7.1

18. Heterotrophs and Their Energy Sources
Majority are chemoheterotrophs that derive both carbon and energy from organic compounds
Saprobes
Free-living microorganisms
Feed primarily on organic detritus from dead organisms
Decomposers of plant litter, animal matter, and dead microbes
Most have rigid cell wall, so they release enzymes to the extracellular environment and digest food particles into smaller molecules
Obligate saprobes- exist strictly on dead organic matter in soil and water
Facultative parasite- when a saprobe infects a host, usually when the host is compromised (opportunistic pathogen)

19. Figure 7.2

20. Other Chemoheterotrophs
Parasites
Derive nutrients from the cells or tissues of a host
Also called pathogens because they cause damage to tissues or even death
Ectoparasites- live on the body
Endoparasites- live in organs and tissues
Intracellular parasites- live within cells
Obligate parasites- unable to grow outside of a living host

21. Transport Mechanisms for Nutrient Absorption
Cells must take nutrients in and transport waste out
Transport occurs across the cell membrane, even in organisms with cell walls

22. The Movement of Water: Osmosis
Osmosis: Diffusion of water through a selectively permeable membrane
The membrane is selectively permeable- having passageways that allow free diffusion of water but can block certain other dissolved molecules
When the membrane is between solutions of differing concentrations and the solute is not diffusible, water will diffuse at a fast rate from the side that has more water to the side that has less water

23. Figure 7.3

24. Osmotic Relationships
The osmotic relationship between cells and their environment is determined by the relative concentrations of the solutions on either side of the cell membrane
Isotonic: The environment is equal in solute concentration to the cell’s internal environment
No net change in cell volume
Generally the most stable environment for cells
Hypotonic: The solute concentration of the external environment is lower than that of the cell’s internal environment
Net direction of osmosis is from the hypotonic solution into the cell
Cells without cell walls swell and can burst
Hypertonic: The environment has a higher solute concentration than the cytoplasm
Will force water to diffuse out of a cell
Said to have high osmotic pressure

25. Figure 7.4

26. Adaptations to Osmotic Variations in the Environment
Example: fresh pond water- hypotonic conditions
Bacteria- cell wall protects them from bursting
Amoeba- a water (or contractile) vacuole that moves excess water out of the cell
Example: high-salt environment- hypertonic conditions
Halobacteria living in the Great Salt Lake- absorb salt to make their cells isotonic with the environment

27. The Movement of Molecules: Diffusion and Transport
Diffusion: When atoms or molecules move in a gradient from an area of higher density or concentration to an area of lower density or concentration
Random thermal movement of molecules will eventually distribute the molecules from an area of higher concentration to an area of lower concentration
Evenly distributes the molecules
Diffusion of molecules across the cell membrane is largely determined by the concentration gradient and permeability of the substance
Simple or passive diffusion is limited to small nonpolar molecules or lipid soluble molecules

28. Figure 7.5

29. Facilitated Diffusion
Utilizes a carrier protein that binds a specific substance, changes the conformation of the carrier protein, and the substance is moved across the membrane
Once the substance is transported, the carrier protein resumes its original shape
Carrier proteins exhibit specificity
Saturation: The rate of a substance is limited by the number of binding sites on the transport proteins
Competition: When two molecules of similar shape can bind to the same binding site on a carrier protein

30. Figure 7.6

31. Active Transport
Nutrients are transported against the diffusion gradient or in the same direction as the natural gradient but at a rate faster than by diffusion alone
Requires the presence of specific membrane proteins (permeases and pumps)
Requires the expenditure of energy
Items that require active transport: monosaccharides, amino acids, organic acids, phosphates, and metal ions
Specialized pumps- an important type of active transport
Group translocation: couples the transport of a nutrient with its conversion to a substance that is immediately useful inside the cell

32. Figure 7.7

33. Endocytosis: Eating and Drinking by Cells
A form of active transport
Transporting large molecules, particles, lipids, or other cells
Occurs in some eukaryotic cells
The cell encloses the substance in its cell membrane, simultaneously forming a vacuole and engulfing it
Phagocytosis- amoebas and certain white blood cells; ingesting whole cells or large solid matter
Pinocytosis- Transport of liquids such as oils or molecules in solution

35. 7.2 Environmental Factors that Influence Microbes
Temperature Adaptations
Microbial cells cannot control their temperature, so they assume the ambient temperature of their natural habitat
The range of temperatures for the growth of a given microbial species can be expressed as three cardinal temperatures:
Minimum temperature: the lowest temperature that permits a microbe’s continued growth and metabolism
Maximum temperature: The highest temperature at which growth and metabolism can proceed
Optimum temperature: A small range, intermediate between the minimum and maximum, which promotes the fast rate of growth and metabolism
Some microbes have a narrow cardinal range while others have a broad one
Another way to express temperature adaptation- to describe whether an organism grows optimally in a cold, moderate, or hot temperature range

36. Psychophile
A microorganism that has an optimum temperature below 15°C and is capable of growth at 0°C.
True psychrophiles are obligate with respect to cold and cannot grow above 20°C.
Psychrotrophs or facultative psychrophiles- grow slowly in cold but have an optimum temperature above 20°C.

37. Figure 7.8

38. Figure 7.9

39. Mesophile An organism that grows at intermediate temperatures
Optimum growth temperature of most: 20°C to 40°C
Temperate, subtropical, and tropical regions
Most human pathogens have optima between 30°C and 40°C

40. Thermophile
A microbe that grows optimally at temperatures greater than 45°C
Vary in heat requirements
General range of growth of 45°C to 80°C
Hyperthermophiles- grow between 80°C and 120°C

41. Gas Requirements
Atmospheric gases that most influence microbial growth- O2 and CO2
Oxygen gas has the greatest impact on microbial growth
As oxygen enters into cellular reactions, it is transformed into several toxic products
Most cells have developed enzymes that go about scavenging and neutralizing these chemicals
Superoxide dismutase
Catalase
Essential for aerobic organisms

42. Several General Categories of Oxygen Requirements
Aerobe: can use gaseous oxygen in its metabolism and possesses the enzymes needed to process toxic oxygen products
Obligate aerobe: cannot grow without oxygen
Facultative anaerobe: an aerobe that does not require oxygen for its metabolism and is capable of growth in the absence of it
Microaerophile: does not grow at normal atmospheric concentrations of oxygen but requires a small amount of it in metabolism
Anaerobe: lacks the metabolic enzyme systems for using oxygen in respiration
Strict, or obligate, anaerobes: also lack the enzymes for processing toxic oxygen and cannot tolerate any free oxygen in the immediate environment and will die if exposed to it.
Aerotolerant anaerobes: do not utilize oxygen but can survive and grow to a limited extent in its presence

43. Figure 7.10

44. Figure 7.11

45. Carbon Dioxide
All microbes require some carbon dioxide in their metabolism
Capnophiles grow best at a higher CO2 tension than is normally present in the atmosphere

46. Effects of pH
Majority of organisms live or grow in habitats between pH 6 and 8
Obligate acidophiles
Euglena mutabilis- alga that grows between 0 and 1.0 pH
Thermoplasma- archae that lives in hot coal piles at a pH of 1 to 2, and would lyse if exposed to pH 7

47. Osmotic Pressure
Most microbes live either under hypotonic or isotonic conditions
Osmophiles- live in habitats with a high solute concentration
Halophiles- prefer high concentrations of salt
Obligate halophiles- grow optimally in solutions of 25% NaCl but require at least 9% NaCl for growth

48. Miscellaneous Environmental Factors
Nonphotosynthetic microbes tend to be damaged by the toxic oxygen products produced by contact with light
Some produce yellow carotenoid pigments to protect against the damaging effects of light by absorbing and dismantling toxic oxygen
Other types of radiation that can damage microbes are ultraviolet and ionizing rays
Barophiles: deep-sea microbes that exist under hydrostatic pressures ranging from a few times to over 1,000 times the pressure of the atmosphere
All cells require water- only dormant, dehydrated cell stages tolerate extreme drying

49. Ecological Associations Among Microorganisms
Most microbes live in shared habitats
Interactions can have beneficial, harmful, or no particular effects on the organisms involved
They can be obligatory or nonobligatory to the members
They often involve nutritional interactions

50. Symbiosis
A general term used to denote a situation in which two organisms live together in a close partnership
Members are termed symbionts
Three main types of symbionts
Mutualism: when organisms live in an obligatory but mutually beneficial relationship
Commensalism: the member called the commensal receives benefits, while its coinhabitant is neither harmed nor benefited
Satellitism: when one member provides nutritional or protective factors needed by the other
Parasitism: a relationship in which the host organism provides the parasitic microbe with nutrients and a habitat

51. Figure 7.12

52. Nonsymbiotic Relationship
Organisms are free-living and relationships are not required for survival
Synergism: an interrelationship between two or more free-living organisms that benefits them but is not necessary for their survival
Antagonism: an association between free-living species that arrises when members of a community compete
One microbe secretes chemical substances into the surrounding environment that inhibit or destroy another microbe in the same habitat

53. Interrelationships Between microbes and Humans
Normal microbiotia: microbes that normally live on the skin, in the alimentary tract, and in other sites in humans
Can be commensal, parasitic, and synergistic relationships

54. 7.3 The Study of Microbial Growth
Growth takes place on two levels
Cell synthesizes new cell components and increases in size
The numer of cells in the population increases
The Basis of Population Growth: Binary Fission

55. Figure 7.13

56. Figure 7.14

57. The Rate of Population Growth
Generation or doubling time: The time required for a complete fission cycle
Each new fission cycle or generation increases the population by a factor of 2
As long as the environment is favorable, the doubling effect continues at a constant rate
The length of the generation time- a measure of the growth rate of an organism
Average generation time- 30 to 60 minutes under optimum conditions
Can be as short as 10 to 12 minutes
This growth pattern is termed exponential

58. Graphing Bacterial Growth
The data from growing bacterial populations are graphed by plotting the number of cells as a function of time
If plotted logarithmically- a straight line
If plotted arithmetically- a constantly curved slope
To calculate thesize of a population over time: Nf = (Ni)2n
Nf is the total number of cells in the population at some point in the growth phase
Ni is the starting number
N denotes the generation number

59. The Population Growth Curve
A population of bacteria does not maintain its potential growth rate and double endlessly
A population displays a predictable pattern called a growth curve
The method to observe the population growth pattern:
Place a tiny number of cells in a sterile liquid medium
Incubate this culture over a period of several hours
Sampling the browth at regulat intervals during incubation
Plating each sample onto solid media
Counting the number of colonies present after incubation

60. Stages in the Normal Growth Curve
Data from an entire growth period typically produce a curve with a series of phases
Lag Phase
Exponential Growth Phase
Stationary Growth Phase
Death Phase

61. Lag Phase Relatively “flat” period
Newly inoculated cells require a period of adjustment, enlargement, and synthesis
The cells are not yet multiplying at their maximum rate
The population of cells is so sparse that the sampling misses them
Length of lag period varies from one population to another

62. Exponential Growth (Logarithmic or log) Phase
When the growth curve increases geometrically
Cells reach the maximum rate of cell division
Will continue as long as cells have adequate nutrients and the environment is favorable

63. Stationary Growth Phase
The population enters a survival mode in which cells stop growing or grow slowly
The rate of cell inhibition or death balances out the rate of multiplication
Depleted nutrients and oxygen
Excretion of organic acids and other biochemical pollutants into the growth medium

64. Death Phase The curve dips downward
Cells begin to die at an exponential rate

65. Figure 7.15

66. Potential Importance of the Growth Curve
Implications in microbial control, infection, food microbiology, and culture technology
Growth patterns in microorganisms can account for the stages of infection
Understanding the stages of cell growth is crucial for working with cultures
In some applications, closed batch culturing is inefficient, and instead, must use a chemostat or continuous culture system

67. Other Methods of Analyzing Population Growth
Turbidometry- a tube of clear nutrient solution becomes turbid as microbes grow in it

68. Figure 7.16

69. Enumeration of Bacteria
Direct or total cell count- counting the number of cells in a sample microscopically
Uses a special microscope slide (cytometer)
Used to estimate the total number of cells in a larger sample

70. Figure 7.17

71. Automated Counting
Coulter counter- electronically scans a culture as it passes through a tiny pipette
Flow cytometer also measures cell size and differentiates between live and dead cells
Real-time PCR allows scientists to quantify bacteria and other microorganisms that are present in environmental or tissue samples without isolating or culturing them

72. Figure 7.18