1. Chapter 7 Microbial Nutrition, Ecology, and Growth
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2. Microbial Nutrition
Nutrition – process by which chemical substances (nutrients) are acquired from the environment and used in cellular activities
Essential nutrients – must be provided to an organism
Two categories of essential nutrients:
Macronutrients – required in large quantities; play principal roles in cell structure and metabolism
Proteins, carbohydrates
Micronutrients or trace elements – required in small amounts; involved in enzyme function and maintenance of protein structure
Manganese, zinc, nickel

3. Copyright © The McGraw-Hill Companies, Inc
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Sunlight supplies the basic source of
energy on earth for most organisms.
Photosynthesizers can use it directly
to produce organic nutrients that feed
other organisms. Non photosynthetic
organisms extract the energy from
chemical reactions to power cell processes.
© Courtesy: Pacific Northwest National Laboratory
Gases: the atmosphere is a reservoir
for nitrogen, oxygen, and carbon dioxide
essential to living processes. °C K 50 40 30 20 10
-10
-20
-30
-40
320
310
300
290
280
270
260
250
240
230
CO2
Plant
litter
Nutrients
Soil
microbes
Soil community
Aquatic microbes
Organic compounds
© Kathy Park Talaro
Nutrients are constantly being formed
by decomposition and synthesis and released into the environment. Many inorganic nutrients originate from
non-living environments such as the
air, water, and bedrock.
Complex communities of microbes exist in nearly every place on earth. Microbes residing in these communities must associate physically and share the habitat, often establishing biofilms and other inter relationships.
The temperature of habitats varies to a significant extent among all places
on earth, and microbes exist at most points along this wide temperature scale. pH
Acidic
[H+]
Neutral
[OH–]
Basic
(alkaline)
Acid
Base
The acid or base content (pH) can show extreme variations from habitat to habitat. Microbes are the most adaptable organisms with regard to pH.

4. Nutrients
Organic nutrients – contain carbon and hydrogen atoms and are usually the products of living things
Methane (CH4), carbohydrates, lipids, proteins, and nucleic acids
Inorganic nutrients – atom or molecule that contains a combination of atoms other than carbon and hydrogen
Metals and their salts (magnesium sulfate, ferric nitrate, sodium phosphate), gases (oxygen, carbon dioxide) and water

5. Chemical Analysis of Cell Contents
70% water
Proteins
96% of cell is composed of 6 elements:
Carbon
Hydrogen
Oxygen
Phosphorous
Sulfur
Nitrogen

6. Essential Biological Nutrients

7. Sources of Essential Nutrients
Carbon sources
Heterotroph – must obtain carbon in an organic form made by other living organisms such as proteins, carbohydrates, lipids, and nucleic acids
Autotroph – an organism that uses CO2, an inorganic gas as its carbon source
Not nutritionally dependent on other living things

8. Growth Factors: Essential Organic Nutrients
Organic compounds that cannot be synthesized by an organism because they lack the genetic and metabolic mechanisms to synthesize them
Growth factors must be provided as a nutrient
Essential amino acids, vitamins

9. Nutritional Types Main determinants of nutritional type are:
Carbon source – heterotroph, autotroph
Energy source
Chemotroph – gain energy from chemical compounds
Phototrophs – gain energy through photosynthesis

10. Nutritional Categories

11. Autotrophs and Their Energy Sources
Photoautotrophs
Oxygenic photosynthesis
Anoxygenic photosynthesis
Chemoautotrophs (lithoautotrophs) survive totally on inorganic substances
Methanogens, a kind of chemoautotroph, produce methane gas under anaerobic conditions
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© Kathy Park Talaro

12. Heterotrophs and Their Energy Sources
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Digestion in Bacteria and Fungi
Majority are chemoheterotrophs
Aerobic respiration
Two categories
Saprobes: free-living microorganisms that feed on organic detritus from dead organisms
Opportunistic pathogen
Facultative parasite
Parasites: derive nutrients from host
Pathogens
Some are obligate parasites
Organic debris
(a)
Walled cell is a barrier.
Enzymes
(b)
Enzymes are transported outside the wall.
(c)
Enzymes hydrolyze the bonds on nutrients.
(d)
Smaller molecules are transported across the
wall and cell membrane into the cytoplasm.

13. Concept Check:
If an organism is degrading large organic molecules to get both carbon and energy, it would be best described as a
Photoheterotroph
Photoautotroph
Chemoheterotroph
Chemoautotroph

14. Transport: Movement of Chemicals Across the Cell Membrane
Passive transport – does not require energy; substances exist in a gradient and move from areas of higher concentration toward areas of lower concentration
Diffusion
Osmosis – diffusion of water
Facilitated diffusion – requires a carrier
Active transport – requires energy and carrier proteins; gradient independent
Active transport
Group translocation – transported molecule chemically altered
Bulk transport – endocytosis, exocytosis, pinocytosis

15. Diffusion – Net Movement of Molecules Down Their Concentration Gradient (Passive Transport)
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How Molecules Diffuse in Aqueous Solutions

16. Osmosis - Diffusion of Water (Passive Transport)
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Glass
tube
Membrane sac
with solution
Solute
Water
Container
with
water
Pore a.
Inset shows a close-up of the osmotic process.
The gradient goes from the outer container
(higher concentration of H2O) to the sac (lower
concentration of H2O). Some water will diffuse
the opposite direction but the net gradient
favors osmosis into the sac. b.
As the H2O diffuses into the sac, the volume
increases and forces the excess solution into
the tube, which will rise continually. c.
Even as the solution becomes diluted, there
will still be osmosis into the sac. Equilibrium
will not occur because the solutions can never
become equal. (Why?)

17. Response to solutions of different osmotic content
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Cells with
Cell Wall
Isotonic Solution
Hypotonic Solution
Hypertonic Solution
Cell wall
Cell
membrane
Cell membrane
Water concentration is equal inside and
outside the cell, thus rates of diffusion
are equal in both directions.
Net diffusion of water is into the cell; this
swells the protoplast and pushes it tightly
against the wall. Wall usually prevents
cell from bursting.
Water diffuses out of the cell and
shrinks the cell membrane away from
the cell wall; process is known as
plasmolysis.
Cells Lacking
Cell Wall
Early
Early
Cell membrane
Late
(osmolysis)
Late
Rates of diffusion are equal
in both directions.
Diffusion of water into the cell causes
it to swell, and may burst it if no
mechanism exists to remove the water.
Water diffusing out of the cell causes
it to shrink and become distorted.
Direction of net water movement.

18. Facilitated Diffusion (Passive Transport)
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Outside
cell
Inside
cell
Outside
cell
Inside
cell
(a)
(b)

19. Carrier Mediated Active Transport
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Membrane
Membrane
Membrane
Protein
Protein
Protein
Protein
Protein
Protein
Extracellular
Intracellular
Extracellular
Intracellular
Extracellular
Intracellular
(a) Carrier-mediated active transport. The membrane proteins (permeases) have attachment sites for essential nutrient molecules. As these
molecules bind to the permease, energy from ATP pumps them into the cell’s interior through special membrane protein channels. Microbes
have these systems for transporting various ions (sodium, iron) and small organic molecules.
Group Translocation
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Membrane
Membrane
Protein
Protein
Protein
Protein
Extracellular
Intracellular
Extracellular
Intracellular
(b) In group translocation, the molecule is actively captured, but along the route of transport, it is chemically altered. By coupling transport
with synthesis, the cell conserves energy.

20. Endocytosis: Eating and Drinking by Cells
Endocytosis: bringing substances into the cell through a vesicle or phagosome
Phagocytosis ingests substances or cells
Pinocytosis ingests liquids
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Phagocytosis
Pinocytosis 4
Microvilli
Pseudopods 3
Liquid enclosed
by microvilli 2
Oil droplet
Vacuoles 1
Vesicle with liquid

21. Summary of Transport Processes

22. Concept Check:
If a cell is in a concentrated glucose solution and the glucose is moving into the cell through a carrier protein, this would be an example of
Diffusion
Facilitated Diffusion
Active Transport
Endocytosis
Pinocytosis

23. Environmental Factors That Influence Microbes
Niche: totality of adaptations organisms make to their habitat
Environmental factors affect the function of metabolic enzymes
Factors include:
Temperature
Oxygen requirements pH
Osmotic pressure
Barometric pressure

24. 3 Cardinal Temperatures
Minimum temperature – lowest temperature that permits a microbe’s growth and metabolism
Maximum temperature – highest temperature that permits a microbe’s growth and metabolism
Optimum temperature – promotes the fastest rate of growth and metabolism

25. 3 Temperature Adaptation Groups
Psychrophiles – optimum temperature below 15oC; capable of growth at 0oC
Mesophiles – optimum temperature 20o-40oC; most human pathogens
Thermophiles – optimum temperature greater than 45oC
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Psychrophile
Optimum
Mesophile
Thermophile
Minimum
Maximum
-15
-10 -5 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90
Temperature °C

26. Gas Requirements Oxygen
As oxygen is utilized it is transformed into several toxic products:
Singlet oxygen (1O2), superoxide ion (O2-), peroxide (H2O2), and hydroxyl radicals (OH-)
Most cells have developed enzymes that neutralize these chemicals:
Superoxide dismutase, catalase
If a microbe is not capable of dealing with toxic oxygen, it is forced to live in oxygen free habitats

27. Categories of Oxygen Requirement
Aerobe – utilizes oxygen and can detoxify it
Obligate aerobe – cannot grow without oxygen
Facultative anaerobe – utilizes oxygen but can also grow in its absence
Microaerophilic – requires only a small amount of oxygen
Anaerobe – does not utilize oxygen
Obligate anaerobe – lacks the enzymes to detoxify oxygen so cannot survive in an oxygen environment
Aerotolerant anaerobes – do not utilize oxygen but can survive and grow in its presence

28. Culturing by Oxygen Requirement
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Photo by Keith Weller, USDA/ARS
© Terese M. Barta, Ph.D.

29. Carbon Dioxide Requirement
All microbes require some carbon dioxide in their metabolism
Capnophile – grows best at higher CO2 tensions than normally present in the atmosphere
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Courtesy and © Becton, Dickinson and Company

30. Effects of pH
Majority of microorganisms grow at a pH between 6 and 8 (neutrophiles)
Acidophiles – grow at extreme acid pH
Alkalinophiles – grow at extreme alkaline pH

31. Osmotic Pressure
Most microbes exist under hypotonic or isotonic conditions
Halophiles – require a high concentration of salt
Osmotolerant – do not require high concentration of solute but can tolerate it when it occurs

32. Other Environmental Factors
Barophiles – can survive under extreme pressure and will rupture if exposed to normal atmospheric pressure

33. Concept Check:
Chlamydomonas nivalis grows on Alaskan glaciers and it’s photosynthetic pigments give the snow a red crust. This organism would be best described as a
Psychrophile
Alkalinophile
Microaerophile
Osmotolerant
Barophile
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Image courtesy Nozomu Takeuchi
Image courtesy Nozomu Takeuchi
(a)
(b)

34. Ecological Associations Among Microorganisms
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Microbial Associations
Symbiotic
Nonsymbiotic
Organisms live in close
nutritional relationships;
required by one or both members.
Organisms are free-living;
relationships not required
for survival .
Mutualism
Obligatory,
dependent;
both members
benefit.
Commensalism
The commensal
benefits;
other member
not harmed.
Parasitism
Parasite is
dependent
and benefits;
host harmed.
Synergism
Members
cooperate
and share
nutrients.
Antagonism
Some members
are inhibited
or destroyed
by others.

35. Ecological Associations
Symbiotic – two organisms live together in a close partnership
Mutualism – obligatory, dependent; both members benefit
Commensalism – commensal member benefits, other member neither harmed nor benefited
Parasitism – parasite is dependent and benefits; host is harmed
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Staphylococcus
aureus
growth
Haemophilus
satellite colonies
© Science VU/Fred Marsik/Visuals Unlimited
Courtesy Arthur Hauck (Germany)

36. Ecological Associations
Non-symbiotic – organisms are free-living; relationships not required for survival
Synergism – members cooperate to produce a result that none of them could do alone
Antagonism – actions of one organism affect the success or survival of others in the same community (competition)
Antibiosis
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NH4+
Cellulose
degrader
(Cellulomonas)
Nitrogen
fixer
(Azotobacter) N2
Glucose

37. Interrelationships Between Microbes and Humans
Human body is a rich habitat for symbiotic bacteria, fungi, and a few protozoa - normal microbial flora
Commensal, parasitic, and synergistic relationships

38. Microbial Biofilms
Biofilms result when organisms attach to a substrate by some form of extracellular matrix that binds them together in complex organized layers
Dominate the structure of most natural environments on earth
Communicate and cooperate in the formation and function of biofilms – quorum sensing

39. Biofilm Formation and Quorum Sensing
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Quorum-dependent
proteins
Chromosome
Inducer
molecule 1 5 4 2 3
Matrix 1
Free-swimming cells settle on a surface and remain there. 2
Cells synthesize a sticky matrix that holds them tightly to
the substrate. 3
When biofilm grows to a certain density (quorum), the cells release
inducer molecules that can coordinate a response. 4
Enlargement of one cell to show genetic induction. Inducer molecule
stimulates expression of a particular gene and synthesis of a protein
product, such as an enzyme. 5
Cells secrete their enzymes in unison to digest food particles.

40. The Study of Microbial Growth
Microbial growth occurs at two levels: growth at a cellular level with increase in size, and increase in population
Division of bacterial cells occurs mainly through binary fission (transverse)
Parent cell enlarges, duplicates its chromosome, and forms a central transverse septum dividing the cell into two daughter cells

41. Binary Fission 1 A young cell at early phase of cycle 2
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A young cell at early phase of cycle 2
A parent cell prepares for division by
enlarging its cell wall, cell membrane, and
overall volume. Midway in the cell, the wall
develops notches that will eventually form
the transverse septum, and the duplicated
chromosome becomes affixed to a special
membrane site. 3
The septum wall grows inward, and the
chromosomes are pulled toward opposite
cell ends as the membrane enlarges. Other
cytoplasmic components are distributed
(randomly) to the two developing cells. 4
The septum is synthesized completely
through the cell center, and the cell
membrane patches itself so that there
are two separate cell chambers. 5
At this point, the daughter cells are divided.
Some species will separate completely as
shown here, while others will remain attached,
forming chains or doublets, for example.
Cell wall
Cell membrane
Chromosome 1
Chromosome 2
Ribsomes

42. Rate of Population Growth
Time required for a complete fission cycle is called the generation, or doubling time
Each new fission cycle increases the population by a factor of 2 – exponential growth
Generation times vary from minutes to days
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4500*
*12
4000
3500
Log of
number
of cells
using the
power
of 2
3000 ( )
Number
of cells
2500 ( ) 11
2000
1500 10
1000 9
500
(b)
Time
Number
of cells 1 2 4 8 16 32
Number of
generations 1 2 3 4 5
Exponential
value 21 22 23 24 25
(2´1)
(2´2)
(2´2´2)
(2´2´2´2)
(2´2´2´2´2)
(a)

43. Rate of Population Growth
Equation for calculating population size over time:
Nƒ = (Ni)2n
Nƒ is total number of cells in the population
Ni is starting number of cells
Exponent n denotes generation time
2n number of cells in that generation

44. Concept Check:
Escherichia coli has a doubling time of 20 minutes. If there are 5 cells at the beginning of the experiment, how many will there be in 3 hours?

45. Viable Plate Count 1 225,000 400,000 675,000 Flask inoculated
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Flask inoculated
Samples taken at equally spaced intervals
(0.1 ml)
60 min
120 min
180 min
240 min
300 min
360 min
420 min
480 min
540 min
600 min
0.1 ml
500 ml
Sample is
diluted in
liquid agar
medium
and poured
or spread
over surface
of solidified
Plates are
incubated,
colonies
are counted
None
Number of
colonies (CFU)
per 0.1 ml
<1* 2 4 7 13 23 45 80
135
230
Total estimated
cell population
in flask
<10,000
5,000
20,000
35,000
65,000 1
15,000
225,000
400,000
675,000
1,150,000
*Only means that too few cells are present to be assayed.

46. The Population Growth Curve
In laboratory studies, populations typically display a predictable pattern over time – growth curve
Stages in the normal growth curve:
Lag phase – “flat” period of adjustment, enlargement; little growth
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Stationary phase 9 8 7
Death phase 6 5
Exponential growth phase
Logrithm (10n) of Viable Cells 4
The final
outcome
varies with the culture. 3 2
Lag phase 5 10 15 20 25 30 35 40
Hours T
otal cells in population, live and dead, at each phase
Few cells
Live cells
Dead cells (not part of count)

47. The Population Growth Curve
Stages in the normal growth curve:
Lag phase
Exponential growth phase – a period of maximum growth will continue as long as cells have adequate nutrients and a favorable environment
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Stationary phase 9 8 7
Death phase 6 5
Exponential growth phase
Logrithm (10n) of Viable Cells 4
The final
outcome
varies with the culture. 3 2
Lag phase 5 10 15 20 25 30 35 40
Hours T
otal cells in population, live and dead, at each phase 47
Few cells
Live cells
Dead cells (not part of count) 47

48. The Population Growth Curve
Stages in the normal growth curve:
Lag phase
Exponential growth phase
Stationary phase – rate of cell growth equals rate of cell death caused by depleted nutrients and O2, excretion of organic acids and pollutants
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Stationary phase 9 8 7
Death phase 6 5
Exponential growth phase
Logrithm (10n) of Viable Cells 4
The final
outcome
varies with the culture. 3 2
Lag phase 5 10 15 20 25 30 35 40 48
Hours T
otal cells in population, live and dead, at each phase
Few cells
Live cells
Dead cells (not part of count) 48

49. The Population Growth Curve
Stages in the normal growth curve:
Lag phase
Exponential growth phase
Stationary phase
Death phase – as limiting factors intensify, cells die exponentially
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Stationary phase 9 8 7
Death phase 6 5
Exponential growth phase
Logrithm (10n) of Viable Cells 4
The final
outcome
varies with the culture. 3 2
Lag phase 5 10 15 20 25 30 35 40 49
Hours T
otal cells in population, live and dead, at each phase
Few cells
Live cells
Dead cells (not part of count) 49

50. Methods of Analyzing Population Growth
Turbidometry – most simple
Degree of cloudiness, turbidity, reflects the relative population size
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Percent of light
transmitted
(1)
© Kathy Park Talaro/Visuals Unlimited
(2)
(a)
(b)

51. Methods of Analyzing Population Growth
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Enumeration of bacteria:
Viable colony count
Direct cell count – count all cells present; automated or manual 2 5 8 9
Automatic
counter
Sample in
liquid
Bacterial
cell
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Tube
Counting orifice
Electronic detector 51 51