Part
II MICROBIAL NUTRITION, GROWTH, AND
CONTROL
6
Microbial Nutrition
CHAPTER OVERVIEW
This chapter describes the basic nutritional requirements of microorganisms. Cells must have a supply of raw
materials and energy in order to construct new cellular components. This chapter also describes the processes
by which microorganisms acquire nutrients and provides information about the cultivation of microorganisms.
CHAPTER OBJECTIVES
After reading this chapter you should be able to:
•
•
•
•
•
list the ten elements that microorganisms require in large amounts (macronutrients/macroelements) and
the six elements that they require in smaller amounts (micronutrients/trace elements)
list the major nutritional categories and give the source of carbon, energy, and electrons for each
compare and contrast the various processes (passive diffusion, facilitated diffusion, active transport,
group translocation) by which cells can obtain nutrients from the environment
describe the various types of culture media for microorganisms (defined/synthetic, complex, selective,
differential) and tell how each is normally used in the study of microorganisms
describe the techniques used to obtain pure cultures (spread plate, streak plate, pour plate)
CHAPTER OUTLINE
I.
Elements of Life
A. Macroelements, also known as macronutrients (C, O, H, N, S, P, K, Ca, Mg, Fe), are required by
microorganisms in relatively large amounts
B. Trace elements or micronutrients (Mn, Zn, Co, Mo, Ni, Cu) are required in trace amounts by most
cells and are often adequately supplied in the water used to prepare media or in the regular media
components
C. Other elements may be needed by particular types of microorganisms
II. Carbon, Hydrogen, Oxygen, and Electrons
A. The requirements for carbon, hydrogen, and oxygen are often satisfied together by the same
molecule
B. Heterotrophs use reduced, preformed organic molecules (usually from other organisms) as carbon
sources
C. Autotrophs use carbon dioxide as their sole or principal carbon source
III. Nutritional Types of Microorganisms
A. All organisms need a source of energy and electrons
1. Energy
a. Phototrophs use light as their energy source
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b. Chemotrophs obtain energy from the oxidation of organic or inorganic compounds
Electrons
a. Lithotrophs use reduced inorganic compounds as their electron source
b. Organotrophs use reduced organic compounds as their electron source
B. Most microorganisms can be categorized as belonging to one of four major nutritional types
depending on their sources of carbon, energy, and electrons:
1. Photolithoautotrophs (photoautotrophs)
2. Chemoorganoheterotrophs (chemoheterotrophs)
3. Photoorganoheterotrophs
4. Chemolithoautotrophs
C. Some organisms show great metabolic flexibility and alter their metabolic patterns in response to
environmental changes; mixotrophic organisms combine lithotrophic and heterotrophic metabolic
processes, relying on inorganic energy sources and organic carbon sources
IV. Nitrogen, Phosphorus, and Sulfur
A. Nitrogen is needed for the synthesis of amino acids, purines, pyrimidines, and other molecules;
depending on the organism, nitrogen can be supplied by organic molecules, by assimilatory nitrate
reduction, or by nitrogen fixation
B. Phosphorus is present in nucleic acids, phospholipids, nucleotides, and other molecules; most
microorganisms use inorganic phosphate to meet their phosphorus needs
C. Sulfur is needed for the synthesis of certain amino acids and other molecules; most microorganisms
meet their sulfur needs by assimilatory sulfate reduction
V. Growth Factors
A. Growth factors are organic compounds required by the cell because they are essential cell
components (or precursors of these components) that the cell cannot synthesize; there are three
major classes:
1. Amino acids—needed for protein synthesis
2. Purines and pyrimidines—needed for nucleic acid synthesis
3. Vitamins—function as enzyme cofactors
VI. Uptake of Nutrients
A. Passive diffusion
1. Passive diffusion is a process by which molecules move from an area of high concentration to
an area of low concentration because of random thermal agitation
2. Passive diffusion requires a large concentration gradient for significant levels of uptake
3. Only a few small molecules (e.g., glycerol, H2O, O2, and CO2) can be taken up by this
mechanism given the amphipathic character of cell membranes
B. Facilitated diffusion
1. Facilitated diffusion is a process that involves a carrier molecule (permease) to increase the
rate of diffusion; it only moves molecules from an area of higher concentration to an area of
lower concentration
2. It requires a smaller concentration gradient than passive diffusion
3. The rate of diffusion plateaus when the carriers become saturated (i.e., when binding and
transporting molecules as rapidly as possible)
4. It is generally more important in eukaryotes than in prokaryotes
C. Active transport
1. Active transport is a process that uses carrier proteins and metabolic energy to move molecules
to the cell interior where the solute concentration is already higher than outside the cell (i.e., it
runs against the concentration gradient)
2. ATP-binding cassette transporters (ABC transporters) use ATP to drive transport against a
concentration gradient; they are observed in bacteria, archaea, and eukaryotes; major
facilitator superfamily (MSF) proteins use the energy of ion gradients created by metabolic
processes
3. Proton motive forces can be used to power active transport
2.
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4.
The active transport of two different substances can be linked: symport is the linked transport
of two substances in the same direction; antiport is the linked transport of two substances in
opposite directions
D. Group translocation
1. In this process molecules are modified as they are transported across the membrane
2. The best known group translocation system is the phosphoenolpyruvate:sugar
phosphotransferase system (PTS), which transports sugars into prokaryotic cells while
phosphorylating them
3. Eukaryotes apparently do not use this type of transport
E. Iron uptake
1. Iron uptake is difficult because of the insolubility of ferric iron
2. Many bacteria and fungi secrete siderophores to transport ferric iron into the cell
VII. Culture Media
A. A culture medium is a solid or liquid preparation used to grow, transport, and store microorganisms
B. Chemical and physical types of culture media
1. Synthetic or defined media—these are media in which all components and their concentrations
are known
2. Complex media—these are media that contain some ingredients of unknown composition
and/or concentration
3. Solidified media are usually made with the addition of agar
C. Functional types of media
a. Supportive media (e.g., tryptic soy broth) are general-purpose media for the growth of
many microorganisms
b. Enriched media are supplemented by blood or other special nutrients to encourage the
growth of fastidious heterotrophs
c. Selective media favor the growth of particular microorganisms and inhibit the growth of
others
d. Differential media distinguish between different groups of bacteria on the basis of their
biological characteristics
VIII. Isolation of Pure cultures
A. A pure culture is a clonal population of cells arising from a single cell
B. Streak Plate - a method used to separate cells on the solid medium such that each colony (a
macroscopically visible growth or cluster of microorganisms on a solid medium) arises from a
single cell; an inoculating loop is used to streak microbes in a pattern that leads to their dilution
C. Spread Plate and Pour Plate - The spread plate uses liquid culture to inoculate solid media and this
is spread over the surface to separate the cells and produce clonal colonies; for pour plates, diluted
liquid culture is mixed in cooled molten agar before being poured into culture dishes
D. Microbial growth on agar surfaces helps microbiologists identify bacteria because individual species
often form colonies of characteristic size, shape, color, and appearance (morphology) on a particular
growth medium; most growth occurs near the edges of the colony
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TERMS AND DEFINITIONS
Place the letter of each term in the space next to the definition or description that best matches it.
____ 1.
____ 2.
____ 3.
____ 4.
____ 5.
____ 6.
____ 7.
____ 8.
____ 9.
____ 10.
____ 11.
____ 12.
____ 13.
____ 14.
____ 15.
____ 16.
____ 17.
____ 18.
____ 19.
____ 20.
____ 21.
____ 22.
Elements required by microorganisms in relatively
large amounts
Elements required in trace amounts sufficiently
supplied in water and regular media components
Organisms that can use carbon dioxide as their sole or
principal source of carbon
Organisms that use reduced, preformed organic
molecules as carbon sources
Organisms that obtain energy from the oxidation of
organic or inorganic compounds
Organisms that obtain electrons from the oxidation of
inorganic compounds
Organisms that obtain electrons from the oxidation of
organic compounds
Organisms that obtain energy from light
Required organic compounds that are essential cell
components (or precursors of such components) and
that cannot be synthesized by the organism
Small organic molecules that make up all or part of
enzyme cofactors
The process in which molecules move from a region of
higher concentration to one of lower concentration as a
result of random thermal agitation
Carrier proteins embedded in the plasma membrane
that increase the rate of diffusion of specific molecules
across selectively permeable membranes
The diffusion process that is aided by action of a
carrier protein
Transport of molecules to areas of higher
concentration (i.e., against a concentration gradient)
with the input of metabolic energy
Linked transport of two substances in the same
direction
Linked transport of two substances in opposite
directions
A process in which molecules are chemically modified
and simultaneously transported into the cell
Low molecular weight molecules that complex with
ferric ion and supply it to the cell
A growth medium in which all components and their
specific concentrations are known
A growth medium that contains some ingredients of
unknown composition and/or concentration
A growth medium that favors the growth of some
microorganisms and inhibits the growth of other
microorganisms
A growth medium that distinguishes between different
groups of bacteria on the basis of their biological
characteristics
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a.
b.
c.
d.
e.
f.
g.
h.
i.
j.
k.
l.
m.
n.
o.
p.
q.
r.
s.
t.
u.
v.
active transport
antiport
autotrophs
chemotrophs
complex medium
differential medium
facilitated diffusion
group translocation
growth factors
heterotrophs
lithotrophs
macronutrients
(macroelements)
micronutrients (trace
elements)
organotrophs
passive diffusion
permeases
phototrophs
selective medium
siderophores
symport
synthetic (defined)
medium
vitamins
MACRONUTRIENTS/MICRONUTRIENTS
Indicate whether each of the following is a macronutrient or a micronutrient and briefly describe how cells use
it.
Element
1. Magnesium (Mg)
Type of Nutrient
Common Uses
2. Zinc (Zn)
3. Oxygen (O)
4. Sulfur (S)
5. Iron (Fe)
6. Manganese (Mn)
7. Nitrogen (N)
8. Cobalt (Co)
9. Phosphorus (P)
10. Carbon (C)
11. Hydrogen (H)
12. Potassium (K)
13. Molybdenum (Mo)
14. Nickel (Ni)
15. Calcium (Ca)
16. Copper (Cu)
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FILL IN THE BLANK
1.
are special culture dishes that consist of two round halves. The top half overlaps
the bottom half.
2.
media contain undefined components such as
, which are protein hydrolysates
prepared by partial proteolytic digestion of meat casein, soy meal, gelatin, and other protein sources.
3. ATP-binding cassette transporters (also known as
) are found in bacteria, archaea,
and eukaryotes. They bind and hydrolyze ATP to drive uptake of sugars or amino acids. Thus, they are an
example of
.
4. Iron uptake is made difficult by the great insolubility of ferric ion. Many bacteria overcome this by
secreting ____________, which are compounds of low molecular weight that can complex with ferric ion
and supply it to the cell.
5. Media that contain some ingredients of unknown chemical composition are called ____________ media.
This type of medium is often used because the nutritional requirements of a particular microbe are
unknown and thus a ____________ medium cannot be constructed.
6. If a solid medium is needed for cultivation of microorganisms, liquid media can be solidified by the
addition of ____________, a sulfated polymer extracted from algae, which can be melted in boiling water
and can be cooled to about
°C before hardening.
7. A macroscopically visible growth or cluster of microorganisms on a solid medium is called a
___________. These growths can be obtained by using
,
, or
methods.
8. In many prokaryotes, sugars are transported into the cell while being phosphorylated. The phosphate
donor for the process is phosphoenolpyruvate and the transport system is called
system. It is an example of
.
9. Mixotrophic organisms combine ____________ and ____________ metabolic processes, relying on
inorganic energy sources and organic carbon sources.
10. Microorganisms of the nutritional type _____________ contribute greatly to the chemical
transformations of elements that continually occur in ecosystems.
NUTRITIONAL TYPES OF MICROORGANISMS
Complete the table below by supplying the missing information.
Nutritional Type
1. Photolithotrophic
autotrophy
2. Photoorganotrophic
heterotrophy
3. Chemolithotrophic
autotrophy
4.
5.
Source of Energy
Source of Electrons
Source of Carbon
Inorganic compounds
Organic compounds
Inorganic compounds
Organic compounds
Organic compounds
Inorganic compounds
Inorganic compounds
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Organic compounds
MULTIPLE CHOICE
For each of the questions below select the one best answer.
1.
2.
3.
Which of the following is NOT a major class
of growth factors?
a. amino acids
b. purines and pyrimidines
c. vitamins
d. All of the above are major classes of
growth factors.
Which of the following processes can be
used to concentrate nutrients from dilute
nutrient sources?
a. active transport
b. group translocation
c. Both (a) and (b) are correct.
d. None of the above are correct.
When there are several transport systems for
the same substance, in what way do the
systems differ?
a. in the energy source they use
b. in their affinity for the transported
solute
c. in the nature of their regulation
d. All of the above are correct.
4.
5.
6.
Which of the following is NOT a
characteristic of active transport?
a. saturable rate of uptake
b. requires an expenditure of metabolic
energy
c. can transport materials against a
concentration gradient
d. All of the above are characteristics of
active transport.
Which of the following can be used as an
energy source by bacteria to drive active
transport?
a. ATP hydrolysis
b. proton motive force
c. Both (a) and (b) are correct.
d. Neither (a) nor (b) is correct.
Which of the following is a good method for
obtaining isolated pure cultures of a
microorganism?
a. spread plate
b. pour plate
c. streak plate
d. All of the above are good methods for
obtaining isolated pure cultures.
SELECTIVE AND DIFFERENTIAL MEDIA
Mannitol salt agar is a culture medium that contains a high salt (NaCl) concentration, mannitol (a fermentable
sugar), and a chemical pH indicator that is yellow at acidic conditions and red at alkaline conditions. (Acids
are released when microorganisms ferment mannitol.) This medium also contains other carbohydrates that
allow growth of nonfermenting, halophilic organisms (i.e., nonfermenting organisms that tolerate high salt
concentrations). Nonhalophilic organisms will not grow on mannitol salt agar.
For each of the following situations, place the letter of the term that best describes the way the medium is
being used. Then list the organism(s) that will grow, the organisms that will not grow, and the color of the pH
indicator.
____ 1.
____ 2.
____ 3.
Onto mannitol salt agar you inoculate a halophilic
mannitol fermenter, a halophilic mannitol
nonfermenter, and a nonhalophilic mannitol fermenter.
Onto mannitol salt agar you inoculate a halophilic
mannitol fermenter and a halophilic mannitol
nonfermenter.
Onto mannitol salt agar you inoculate a halophilic
mannitol nonfermenter that is pigmented yellow, and a
halophilic mannitol nonfermenter that is pigmented
red. These two organisms show the same pigmentation
(yellow and red, respectively) on a general purpose
medium such as nutrient agar.
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____ 4.
Onto mannitol salt agar
you inoculate a
halophilic mannitol
nonfermenter and a
nonhalophilic mannitol
fermenter.
a.
b.
c.
selective medium
differential medium
both selective and differential mediums
d.
neither selective nor
differential medium
TRUE/FALSE
____ 1.
____ 2.
____ 3.
____ 4.
____ 5.
____ 6.
____ 7.
____ 8.
____ 9.
____ 10.
____ 11.
____ 12.
____ 13.
____ 14.
Micronutrients are normally a part of enzymes and cofactors where they aid in the catalysis of
reactions and the maintenance of protein structure.
Most microorganisms require large amounts of sodium (Na).
Transport of materials against a concentration gradient that requires expenditure of metabolic
energy is called facilitated diffusion.
Permease proteins resemble enzymes in their specificity for the substance to be transported; each
carrier is selective and will transport only closely related solutes.
Microorganisms usually have only one transport system for each nutrient.
Agar is an excellent hardening agent because it is not usually degraded by microorganisms.
Media can be selective or differential, but cannot be both selective and differential.
Heterotrophs usually obtain preformed, partially reduced organic molecules from other organisms.
Facilitated diffusion is generally more important in prokaryotes than in eukaryotes.
Quantitative growth-response assays use the growth of microorganisms as a way of measuring the
amount of a specific, limited growth nutrient in a particular growth medium.
Nitrogen, phosphorous, and sulfur may be obtained from organic molecules and by reduction and
assimilation of oxidized inorganic molecules.
Generally, the most rapid growth occurs at the center of a colony, where nutrients and other
resources are more plentiful.
Most nutrients needed by cells are brought into the cell with the aid of carrier proteins.
Colony size and appearance can help microbiologist identify bacteria.
CRITICAL THINKING
1.
In this figure, which line corresponds to the situation for passive diffusion? Which line corresponds to the
situation for facilitated diffusion? Explain.
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2.
A great majority of microorganisms studied thus far are either photolithotrophic autotrophs or
chemoorganotrophic heterotrophs. Why? Where would you expect to find photolithotrophic
heterotrophs? Chemolithotrophic autotrophs?
3.
Many bacteria have several different mechanisms for transport of a single substance. Compare the
advantages of multiple mechanisms with those of a single transport mechanism for any given substance.
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ANSWER KEY
Terms and Definitions
1. l, 2. m, 3. c, 4. j, 5. d, 6. k, 7. n, 8. q, 9. i, 10. v, 11. o, 12. p, 13. g, 14. a, 15. t, 16. b, 17. h, 18. s,
19. u, 20. e, 21. r, 22. f
Macronutrients/Micronutrients
1. macro, 2. micro, 3. macro, 4. macro, 5. macro, 6. micro, 7. macro, 8. micro, 9. macro, 10. macro,
11. macro, 12. macro, 13. micro, 14. micro, 15. macro, 16. micro
Fill in the Blank
1. culture dishes 2. complex; peptones 3. ABC transporters; active transport 4. siderophores 5. complex;
defined 6. agar; 40 7. colony; spread plate; streak plate; pour plate 8. phosphoenolpyruvate: sugar
phosphotransferase; group translocation 9. lithotrophic; heterotrophic 10. chemolithotroph
Nutritional Types of Microorganisms
1. light; CO2 2. light; organic 3. inorganic; CO2 4. chemoorganotrophic heterotroph; organic 5. mixotroph
Multiple Choice
1. d, 2. c, 3. d, 4. d, 5. c, 6. d
Selective and Differential Media
1. c, 2. b, 3. d, 4. a
True/False
1. T, 2. F, 3. F, 4. T, 5. F, 6. T, 7. F, 8. T, 9. F, 10. T, 11. T, 12. F, 13. T, 14. T
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