biology

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Chapter 6
Microbial Nutrition

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Elements of Life - 1
• macroelements (macronutrients)
– C, O, H, N, S, P
• found in organic molecules such as
proteins, lipids, carbohydrates, and
nucleic acids
– K, Ca, Mg, and Fe
• cations and serve in variety of roles
including enzymes, biosynthesis
– required in relatively large amounts

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Table 6.1

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Elements of Life - 2
• micronutrients (trace elements)
– Mn, Zn, Co, Mo, Ni, and Cu
– required in trace amounts
– often supplied in water or in media
components
– ubiquitous in nature
– serve as enzymes and cofactors
• some unique substances may be required

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Carbon, Hydrogen, Oxygen,
and Electrons
• carbon is backbone of all organic
components present in cell
• hydrogen and oxygen are also found
in organic molecules
• electrons play a role in energy
production and reduction of CO2 to
form organic molecules

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Requirements for Carbon,
Hydrogen, and Oxygen
• often satisfied together
– carbon source often provides H, O, and electrons
• heterotrophs
– use organic molecules as carbon sources which often
also serve as energy source
– can use a variety of carbon sources
• autotrophs
– use carbon dioxide as their sole or principal carbon
source
– must obtain energy from other sources

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Table 6.2

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Nutritional Types of Organisms
• based on energy source
– phototrophs use light
– chemotrophs obtain energy from
oxidation of chemical compounds
• based on electron source
– lithotrophs use reduced inorganic
substances
– organotrophs obtain electrons from
organic compounds

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Classes of Major Nutritional
Types
• majority of microorganisms known
– photolithoautotrophs (photoautotrophs)
– chemoorganoheterotrophs
(chemoheterotrophs)
• majority of pathogens
• ecological importance
– photoorganoheterotrophs
– chemolithoautotrophs
– chemolithotrophs

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Table 6.3

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Figure 6.1

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Microorganisms May Change
Nutritional Type
• some have great metabolic flexibility
based on environmental
requirements
• provides distinct advantage if
environmental conditions change
frequently

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Figure 6.2

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Requirements for Nitrogen,
Phosphorus, and Sulfur
• needed for synthesis of important
molecules (e.g., amino acids, nucleic
acids)
• nitrogen supplied in numerous ways
• phosphorus usually supplied as inorganic
phosphate
• sulfur usually supplied as sulfate via
assimilatory sulfate reduction

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Sources of Nitrogen
• organic molecules
• ammonia
• nitrate via assimilatory nitrate
reduction
• nitrogen gas via nitrogen fixation

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Sources of Phosphorus and
Sulfur
• phosphorus
– most organisms use inorganic
phosphorus which is directly
incorporated into their cells
• sulfur
– most organisms use sulfate and reduce
it by assimilatory sulfate reduction

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Growth Factors
• organic compounds
• essential cell components (or their
precursors) that the cell cannot
synthesize
• must be supplied by environment if
cell is to survive and reproduce

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Classes of Growth Factors
• amino acids
– needed for protein synthesis
• purines and pyrimidines
– needed for nucleic acid synthesis
• vitamins
– function as enzyme cofactors??
• Heme
– Function in O2 binding

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Table 6.4

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Microbial Production of
Growth Factors
• microorganisms can synthesize
many growth factors
• large-scale industrial production of
growth factors, such as vitamins

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Uptake of Nutrients
• microbes can only take in dissolved
particles across a selectively permeable
membrane
• some nutrients enter by passive diffusion
• microorganisms use transport
mechanisms
– facilitated diffusion – all microorganisms
– active transport – all microorganisms
– group translocation – Bacteria and Archaea
– endocytosis – Eukarya only

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Passive Diffusion
• molecules move from region of
higher concentration to one of lower
concentration between the cell’s
interior and the exterior
• H2O, O2, and CO2 often move across
membranes this way

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Facilitated Diffusion
• similar to passive diffusion
– movement of molecules is not energy
dependent
– direction of movement is from high
concentration to low concentration
– size of concentration gradient impacts
rate of uptake

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Facilitated Diffusion…
• differs from passive diffusion
– uses membrane bound carrier molecules
(permeases)
– smaller concentration gradient is required
for significant uptake of molecules
– effectively transports glycerol, sugars, and
amino acids
• more prominent in eukaryotic cells than
in bacteria or archaea

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Figure 6.3
•rate of facilitated
diffusion increases
more rapidly and
at a lower
concentration
•diffusion rate
reaches a plateau
when carrier
becomes
saturated

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Figure 6.4

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Active Transport
• energy-dependent process
– ATP or proton motive force used
• move molecules against the gradient
• concentrates molecules inside cell
• involves carrier proteins (permeases)
– carrier saturation effect is observed at
high solute concentrations

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ABC Transporters
• primary active transporters use ATP
• ATP-binding cassette transporters
• observed in Bacteria, Archaea, and
eukaryotes
• Consist of
– 2 hydrophobic membrane spanning domains
– 2 cytoplasmic associated ATP-binding domains
– Substrate binding domains

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Figure 6.5

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Secondary Active Transport
• major facilitator superfamily (MFS)
• use ion gradients to cotransport
substances
– protons
– symport – two substances both move in
the same direction
– antiport – two substances move in
opposite directions

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Figure 6.6

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Group Translocation
• energy dependent transport that
chemically modifies molecule as it is
brought into cell
• best known translocation system is
phosphoenolpyruvate: sugar
phosphotransferase system (PTS)
– many anaerobic bacteria transport sugars
while phosphorylating them using
phosphoenolpyruvate (PEP) as the
phosphate donor

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Figure 6.7

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Iron Uptake
• microorganisms
require iron
• ferric iron is very
insoluble so uptake is
difficult
• microorganisms
secrete siderophores
to aid uptake
• siderophore
complexes with ferric
ion
• complex is then
transported into cell
Figure 6.8

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Culture Media
• need to grow, transport, and store
microorganisms in the laboratory
• culture media is solid or liquid
preparation
• must contain all the nutrients required by
the organism for growth
• classification
– chemical constituents from which they are
made
– physical nature
– function

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Table 6.5

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Chemical and Physical
Types of Culture Media
Defined or synthetic
Complex

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Defined or Synthetic Media
• all components
and their
concentrations
are known
Table 6.6

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Complex Media
• contain some
ingredients of
unknown
composition
and/or
concentration
Table 6.7

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Some Media Components
• peptones
– protein hydrolysates prepared by partial
digestion of various protein sources
• extracts
– aqueous extracts, usually of beef or yeast
• agar
– sulfated polysaccharide used to solidify
liquid media; most microorganisms cannot
degrade it

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Functional Types of Media
Supportive
Enriched
Selective
Differential

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Functional Types of Media
• supportive or general purpose media
– support the growth of many
microorganisms
– e.g., tryptic soy agar
• enriched media
– general purpose media supplemented
by blood or other special nutrients
– e.g., blood agar

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Figure 6.9

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Selective Media
• favor the growth of some
microorganisms and inhibit growth
of others
• e.g., MacConkey agar
– selects for gram-negative bacteria

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Differential Media
• distinguish between different groups of
microorganisms based on their biological
characteristics
• e.g., blood agar
– hemolytic versus nonhemolytic bacteria
• e.g., MacConkey agar
– lactose fermenters versus nonfermenters

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Table 6.8

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Isolation of Pure Cultures
• population of cells arising from a
single cell developed by Robert Koch
• allows for the study of single type of
microorganism in mixed culture
• spread plate, streak plate, and pour
plate are techniques used to isolate
pure cultures

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The Streak Plate
• involves technique of spreading a
mixture of cells on an agar surface
so that individual cells are well
separated from each other
– involves use of bacteriological loop
• each cell can reproduce to form a
separate colony (visible growth or
cluster of microorganisms)

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Figure 6.10

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The Spread Plate and Pour
Plate
• spread plate
– small volume of diluted mixture containing
approximately 30–300 cells is transferred
– spread evenly over surface with a sterile bent rod
• pour plate
– sample is serially diluted
– diluted samples are mixed with liquid agar
– mixture of cells and agar are poured into sterile
culture dishes
• both may be used to determine the number of
viable microorganisms in an original sample

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Figure 6.11

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Figure 6.12

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Microbial Growth on Solid
Surfaces
• colony characteristics that develop when
microorganisms are grown on agar
surfaces aid in identification
• microbial growth in biofilms is similar
• differences in growth rate from edges to
center is due to
– oxygen, nutrients, and toxic products
– cells may be dead in some areas

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Figure 6.13