BIOL 3340
Chapter 6
Chapter 6
Microbial Nutrition
The Common Nutrient
Requirements
All organisms need Carbon, hydrogen, oxygen,
& a source of electrons:
•Macroelements (macronutrients)
C, O, H, N, S, P, K, Ca, Mg, and Fe
required in relatively large amounts
•Micronutrients (trace elements)
Mn, Zn, Co, Mo, Ni, and Cu
required in trace amounts
often supplied in water or in media components
Energy Source
Energy Source
 Phototroph:
 Uses
light as an energy source
 Chemotroph:
 Uses
energy from the oxidation of reduced
chemical compounds
…Nutrition Why?
Carbon is backbone of all organic components
present in cell
 Hydrogen and oxygen are also found in organic
molecules
 Electrons play a role in 1.) energy production
and 2.) biosynthesis of macromolecules

….Types of Nutrition
. Depending on the mode of nutrition
organisms can be categorised:

Heterotrophs


use organic molecules as carbon sources which often
also serve as energy source
Autotrophs


use carbon dioxide as their sole or principal carbon
source
must obtain energy from other sources
Nutritional Types of
Microorganisms
Table 6.2
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Requirements for Nitrogen,
Phosphorus, and Sulfur
Nitrogen is needed for synthesis of
important molecules such as amino
acids, Nucleic acids,
carbohydrates,lipids, enzyme co-factors
and other substances
 nitrogen
is a component of amino acids
 phosphorus is a component of
phospholipids and nucleic acids
 sulfur is found in the amino acids cysteine
and methionine
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Sources of Nitrogen
Microorganisms can get nitrogen from:
 organic molecules
 Nitrogen in ammonia
 nitrate via nitrate reduction to ammonia
(phototrophs and Chemotrophs)
 nitrogen gas via nitrogen fixation
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…Nitrogen Cycle
Sources of Phosphorus
Phosphorus:
 Is present in nucleic acids, phospholipids,
co-factors, some proteins and other cell
components.
 most organisms use inorganic phosphorus,
which is directly incorporated into their
cells
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Sources of Sulphur
Sulfur:
 Is needed for synthesis of some amino
acids (cysteine & methionine),
carbohydrates, biotin and thiamine.
 Most organisms use sulfate and reduce it
by assimilatory sulfate reduction to
sulphur.
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13
Growth Factors
Not all microorganisims have the necessary
enzymes or biochemical pathways to
synthesis all cell components.
 Growth factors- essential cell components
(or their precursors) that the cell cannot
synthesize
 Hence, 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
 Small organic molecules, needed in small
amounts for growth
 function as enzyme cofactors

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Practical Applications of Growth
Factors

Many microorganisms are used to
manufacture large quantities of vitamins
needed for human use
vitamin C produced by Gluconobacter,
Vitamin B12 by Streptomyces ( Refer text bk
for more e.g), Vit D by Saccharomyces
 E.g.,
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Uptake of Nutrients
by the Cell
Some nutrients enter by passive diffusion
 Most nutrients enter by:

 facilitated
diffusion
 active transport
 group translocation
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Passive Diffusion
Molecules move from region of higher
concentration to one of lower
concentration, with rate dependent on size
of the concentration gradient between the
cell exterior and interior
 Small molecules e.gH2O, O2 and CO2 often
move across membranes.

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Facilitated Diffusion
Few similarities to passive diffusion:
 Movement
of substances across a
membrane with the assistance of a
transport protein
 movement of molecules is not energy
dependent
 direction of movement is from high
concentration to low concentration
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Facilitated Diffusion…cont’d

Few differences from passive diffusion
 uses
carrier molecules (permeases) that
transport closely related solutes
 smaller concentration gradient is required for
significant uptake of molecules
 effectively transports glycerol, sugars, and
amino acids

more prominent in eucaryotic cells than in
procaryotic cells
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•rate of facilitated
diffusion increases
more rapidly and
at a lower
concentration
•diffusion rate in
facilitated diffusion
reaches a plateau
when carrier becomes
saturated
Figure 6.3
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…….Model of facilitated Diffusion
Figure 6.4
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Active Transport
Movement of substances across a membrane with
the assistance of a transport protein
(permeases).Active transport pumps are
usually carrier proteins.
 Energy-dependent process ( ATP)
 Moves molecules against the
concentration gradient i.e Movement of
solutes from low  high concentration
 Concentrates molecules inside cell.
 E.g ATP/ABC Transporters
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…Active transport



ATP-binding cassette transporters (ABC
transporters):
The target solute binds to a soluble cassette protein (in
periplasm of gram-negative bacterium, or located bound
to outer leaflet of plasma membrane in gram-positive
bacterium).
The target-cassette complex then binds to an integral
membrane ATPase pump that transports the target
across the plasma membrane.
..ATP/ABC Transporters
ATP-binding
cassette
transporters
 observed in
Bacteria,
Archaea, and
eucaryotes

Figure 6.5
25
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Group Translocation
Group translocation system: A
molecule is transported while being
chemically modified.
 For e.g this GTS transports a variety of
sugars while phosphorylating them to
sugar phosphotransferase systems (PTS):
PEP (phosphoenolpyruvate) + sugar
(outside) pyruvate + sugar-phosphate
(inside)(PTS)

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….Group Translocation
Iron Uptake
 Ferric iron is very insoluble so uptake is
difficult
 Microorganisms use siderophores ( Greek for
Iron bearers), low molecular weight organic
molecules to aid uptake of Ferric iron.

Siderophore complexes with ferric ion
complex is then transported into cell.
Figure 6.8
27
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Culture Media
Most 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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Types of Media
Table 6.4
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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
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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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Enriched media:
1. Blood Agar culture
from human throat
2. Chocolate Agar use to grow
sexually transmitted disease
Neisseria gonorrhoeae
Figure 6.9
32
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…Types of Media
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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…Types of Media
Differential media
 distinguish
between different groups of
microorganisms based on their biological
characteristics
 e.g., blood agar
 hemolytic
 e.g.,
versus nonhemolytic bacteria
MacConkey agar
 lactose
fermenters versus nonfermenters
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Isolation of Pure Cultures
Pure culture:
 population
of cells arising from a single cell
Plating:
 spread plate, streak plate, and pour plate
are techniques used to isolate pure
cultures
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The Streak Plate and
Spread Plate
involve spreading a mixture of cells on an
agar surface so that individual cells are
well separated from each other
 each cell can reproduce to form a
separate colony (visible growth or cluster
of microorganisms)

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Spread Plate Technique
1. dispense cells onto
medium in petri dish
Figure 6.11 (a)
4. spread cells
across surface
2. - 3. sterilize spreader
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Streak Plate Technique
Figure 6.10
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Appearance of a Spread Plate
Figure 6.11 (b)
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The Pour Plate
sample is diluted several times
 diluted samples are mixed with liquid agar
 mixture of cells and agar are poured into
sterile culture dishes

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Figure 6.12
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Colony Growth

most rapid at edge of colony
 oxygen
edge
and nutrients are more available at
slowest at center of colony
 in nature, many microorganisms form
biofilms on surfaces
 colony morphology is sometimes useful in
identifying organisms

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Bacterial Colony Morphology
Figure 6.13 (a)
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Bacterial Colony Morphology
Commonly observed
colonies
Bacillus subtilis-
snowflakes colonies
on nutrient- poor
agar.
Figure 6.13 (b) and (c)
44
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Bibliography
Lecture PowerPoints Prescott’s Principles of
Microbiology-Mc Graw Hill Co.
 http://en.wikipedia.org/wiki/Scientific_metho
d
 https://files.kennesaw.edu/faculty/jhendrix/bi
o3340/home.html
 http://student.ccbcmd.edu/courses/bio141/lec
guide/unit3/viruses/ssvir.html
