D. Parasitism describes an association where one organism (the parasite) benefits while harming the other organism (the host) to some extent.

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Chapter 6
Microbial Nutrition &
Growth

2. Learning Objective Section 6.1
• List the essential nutrients of a bacterial
cell.
• Differentiate between macronutrients and
micronutrients.
• List and define four different terms that
describe an organism’s sources of carbon
and energy.
• Compare and contrast the processes of
diffusion and osmosis.

3. Learning Objectives Section 6.1
(cont’d)
• Identify the effects of isotonic, hypotonic,
and hypertonic conditions on a cell.
• Name two types of passive transport and
one type of active transport.

4. Microbial Nutrition
• Essential nutrient: any substance that must
be provided to an organism
• Macronutrients: required in relatively large
quantities and play principal roles in cell
structure and metabolism
- Carbon, hydrogen, and oxygen
• Micronutrients: also known as trace
elements
- Present in much smaller amounts and are
involved in enzyme function and maintenance of
protein structure
- Examples: manganese, zinc, nickel

5. Microbial Nutrition (cont’d)
• Inorganic nutrient
- An atom or simple molecule that contains a
combination of atoms other than carbon and
hydrogen
- Found in the crust of the earth, bodies of water,
and the atmosphere
• Organic nutrients
- Contain carbon and hydrogen atoms and are the
products of living things
- Simple organic molecules such as methane
- Large polymers (carbohydrates, lipids, proteins,
nucleic acids)

6. Chemical Analysis of the
Microbial Cytoplasm
• Water – 70% of all components
• Proteins
• Organic compounds – 97% of dry cell weight
• Elements CHONPS – 96% of dry cell weight
• Most chemical elements available to the cell
as compounds and not as pure elements
• Only a few types of nutrients needed to
synthesize over 5,000 different compounds

8. What Microbes Eat
• Heterotroph: an organism that must obtain
its carbon in an organic form
• Autotroph: an organism that uses inorganic
CO2 as its carbon source
- Has the capacity to convert CO2 into organic
compounds
- Not nutritionally dependent on other living
things
• Phototroph: microbes that photosynthesize
• Chemotroph: microbes that gain energy from
chemical compounds

10. Autotrophs and
Their Energy Sources
• Photoautotrophs:
- Photosynthetic:
• Produce organic molecules using CO2 that can
be used by themselves and by heterotrophs
• Chemoautotrophs:
- Chemoorganic autotrophs: use organic
compounds for energy and inorganic
compounds as a carbon source
- Lithoautotrophs: rely totally on inorganic
minerals and require neither sunlight nor
organic nutrients

11. Heterotrophs and
Their Energy Sources
• Chemoheterotrophs:
- Derive both carbon and energy from organic
compounds
- Process these molecules through respiration or
fermentation
• Saprobes:
- Free-living organisms that feed on organic
detritus from dead organisms
- Decomposers of plant litter, animal matter, and
dead microbes
- Recycle organic nutrients

12. Heterotrophs and
Their Energy Sources (cont’d)
• Parasites:
- Derive nutrients from the cells or tissues of a
living host
- Pathogens: cause damage to tissues or even
death
- Range from viruses to helminths
- Ectoparasites: live on the body
- Endoparasites: live in the organs and tissues
- Intracellular parasites: live within cells such as
the leprosy bacillus and the syphilis spirochete
- Obligate parasites: unable to grow outside of a
living host

14. Other Important Nutrients
• Sodium (Na): important for certain types of
cell transport
• Calcium (Ca): stabilizer of cell wall and
endospores of bacteria
• Magnesium (Mg): component of chlorophyll
and a stabilizer of membranes and ribosomes
• Iron (Fe): important component of the
cytochrome proteins of cell respiration
• Zinc (Zn): essential regulatory element for
eukaryotic genetics

15. Temperature
• Cardinal temperatures: the range of
temperatures for the growth of a given
microbial species
- Minimum temperature: the lowest temperature
that permits a microbe’s continued growth and
metabolism; below this temperature, its activities
are limited
- Maximum temperature: the highest temperature
at which growth and metabolism can proceed
before proteins are denatured
- Optimum temperature: an intermediate between
the minimum and the maximum that promotes the
fastest rate of growth and metabolism

16. Temperature (cont’d)
• Psychrophiles:
- Optimum temperature below 15°C
- Capable of growth at 0°C
- Obligate with respect to cold and cannot grow
above 20°C
- Storage at refrigerator temperature incubates
rather than inhibits them
- Natural habitats of psychrophilic bacteria,
fungi, and algae are lakes, rivers, snowfields,
polar ice, and the deep ocean.
- Rarely pathogenic

17. Temperature (cont’d)
• Psychrotrophs:
- Grow slowly in the cold but have an
optimum temperature between 15°C
and 30°C
- Staphylococcus aureus and Listeria
monocytogenes are able to grow at
refrigerator temperatures and cause
food-borne disease.

18. Temperature (cont’d)
• Mesophiles:
- Majority of medically significant
microorganisms
- Grow at intermediate temperatures
between 20°C and 40°C
- Inhabit animals and plants as well as
soil and water in temperate, subtropical,
and tropical regions
- Human pathogens have optimal
temperatures between 30°C and
40°C

19. Temperature (cont’d)
• Thermoduric:
- Can survive short exposure to high
temperatures but are normally
mesophiles
- Common contaminants of heated or
pasteurized foods
- Examples are heat-resistant cysts such
as Giardia and sporeformers such as
Bacillus and Clostridium.

20. Temperature (cont’d)
• Thermophile:
- Grows optimally at temperatures greater than
45°C
- Live in soil and water associated with volcanic
activity, compost piles, and in habitats directly
exposed to the sun
- Vary in heat requirements with a range of growth
of 45°C to 80°C
- Most eukaryotic forms cannot survive above
60°C
• Extreme thermophiles grow between 80°C
and 121°C

22. Gases
• The atmospheric gases that influence
microbial growth are O2 and CO2
- O2 has the greatest impact on microbial growth.
- O2 is an important respiratory gas and a
powerful oxidizing agent.
• Microbes fall into one of three categories:
- Those that use oxygen and detoxify it.
- Those that can neither use oxygen nor detoxify
it.
- Those that do not use oxygen but can detoxify it.

23. How Microbes Process Oxygen
• As oxygen enters cellular reactions, it is
transformed into several toxic products:
- Singlet oxygen (O): an extremely reactive
molecule that can damage and destroy a cell
by the oxidation of membrane lipids
- Superoxide ion (O2
-): highly reactive
- Hydrogen peroxide (H2O2): toxic to cells and
used as a disinfectant
- Hydroxyl radicals (OH-): also highly reactive

24. How Microbes Process
Oxygen (cont’d)
• Most cells have developed enzymes that scavenge
and neutralize reactive oxygen byproducts.
• Two-step process requires two enzymes:
• Superoxide ion is converted into hydrogen peroxide by
superoxide dismutase.
• Hydrogen peroxide is converted into harmless water and
oxygen by catalase.

26. Carbon Dioxide
• Capnophiles: organisms that grow best at
a higher CO2 tension than is normally
present in the atmosphere
• Important in the initial isolation of the
following organisms from clinical
specimens:
- Neisseria (gonorrhea, meningitis)
- Brucella (undulant fever)
- Streptococcus pneumoniae

27. pH
• Defined as the degree of acidity or alkalinity
of a solution:
- Expressed by the pH scale, a series of numbers
ranging from 0 to 14
- 7.0 is the pH of pure water
- As the pH value decreases toward 0, the acidity
increases
- As the pH value increases toward 14, the
alkalinity increases
• The majority of organisms live or grow in
habitats between pH 6 and 8.

28. pH (cont’d)
• Acidophiles: organisms that thrive in acidic
environments
- Euglena mutabilis: grows in acid pools between pH 0 and 1
- Thermoplasma: lives in coal piles at a pH of 1 or 2
- Picrophilus: thrives at a pH of 7, but can live at a pH of 0
- Many molds and yeasts tolerate acid and are the primary
spoilage agents of pickled foods
• Alkalinophiles: organisms that thrive in alkaline
conditions
- Natromonas: live in hot pools and soils at pH 12
- Proteus: can create alkaline conditions to neutralize urine
and colonize and infect the urinary system

29. Osmotic Pressure
• Osmophiles: live in habitats with high solute
concentration
• Halophiles: prefer high concentration of salt
- Obligate halophiles: Halobacterium and Halococcus
grow optimally at solutions of 25% NaCl but require at
least 9% NaCl.
- Facultative halophiles: remarkably resistant to salt,
even though they do not normally reside in high salt
environments
- Staphylococcus aureus can grow on NaCl media
ranging from 0.1% to 20%.

30. Radiation
• Phototrophs use visible light rays as an energy
source.
• Nonphotosynthetic microbes tend to be
damaged by the toxic oxygen products produced
by contact with light.
• Some microbial species produce yellow
carotenoid pigments to absorb and dismantle
toxic oxygen.
• Ultraviolet and ionizing radiation can be used in
microbial control.

31. Pressure
• Barophiles:
–Exist under pressures that range from a
few times to over 1,000 times the
pressure of the atmosphere
- These bacteria are so strictly adapted to
high pressures that they will rupture
when exposed to normal atmospheric
pressure.

32. Other Organisms
• In all but the rarest instances, microbes live in
shared habitats:
– Associations between similar or dissimilar types
of microbes
- Associations with multicellular organisms, such
as animals or plants
- Interactions can be beneficial, harmful, or have
no particular effect.
- Interactions can be obligatory or nonobligatory to
the members.
- Often involve nutritional interactions

34. Strong Partnerships: Symbioses
• Symbiosis: a general term to denote a situation in
which two organisms live together in a close
partnership
- Symbionts: members of a symbiosis
• Three main types of symbiosis occur
- Mutualism: organisms live in an obligatory but
mutually beneficial relationship
- Commensalism: the partner called the commensal
receives benefits, while its partner is neither harmed
nor benefitted
- Parasitism: a relationship in which the host organism
provides the parasitic microbe with nutrients and a
habitat; parasite usually harms the host to some
extent

35. Associations But Not
Partnerships
• Antagonism: an association between free-living
species that arises when members of a
community compete
- Antibiosis: the production of inhibitory compounds
such as antibiotics into the surrounding environment
that inhibit or destroy another microbe in the same
habitat
- The first microbe has a competitive advantage by
increasing the space and nutrients available to it.
- Common in the soil where mixed communities
compete for space and food

36. Associations But Not
Partnerships (cont’d)
• Synergism:
– An interrelationship between two organisms
that benefits them but is not necessary for
survival
– Together the participants cooperate to
produce a result that none of them could do
alone
– Gum disease, dental caries, and some
bloodstream infections involve mixed
infections that are examples of bacteria
interacting synergistically.

37. Biofilms:
The Epitome of Synergy
• Mixed communities of bacteria and other
microbes that are attached to a surface and
each other.
• Formation of a biofilm:
– A “pioneer” colonizer initially attaches to a surface.
– Other microbes then attach to those bacteria or a
polymeric sugar or protein substance secreted by
the microbial colonizers.
– Attached cells are stimulated to release chemicals
as the cell population grows.

38. Biofilms:
The Epitome of Synergy (cont’d)
• Quorum sensing: used by bacteria to interact
with members of the same species as well as
members of other species that are close by
• Structure of the biofilm:
- Large, complex communities form with different
physical and biological characteristics.
- The bottom may have very different pH and oxygen
conditions than the surface.
- Partnership among multiple microbial inhabitants
- Cannot be eradicated by traditional methods

39. Biofilms:
The Epitome of Synergy (cont’d)
• Bacteria in biofilms behave and respond
very differently than planktonic (free-living)
bacteria:
- Different genes are activated
- Behave and respond very differently to their
environments

41. Concept Check
Which of the following describes an
association between microbes in which one
organism is benefitted and one is harmed in
some way?
A. Mutualism
B. Synergism
C. Commensalism
D. Parasitism
E. Antagonism