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Chapter 7
Microbial Nutrition, Ecology, and Growth
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
2
7.1 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
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
© Kathy Park Talaro
Gases: the atmosphere is a reservoir
for nitrogen, oxygen, and carbon dioxide
essential to living processes.
Plant
litter
Soil
microbes
Nutrients
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.
CO2
The acid or base content (pH) can show extreme variations
from habitat to habitat. Microbes are the most adaptable
organisms with regard to pH.
Acid Base
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. Acidic Neutral
Basic
(alkaline)
pH 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14
Soil community Aquatic microbes Organic compounds
[OH–] [H+]
K °C
320
310
300
290
280
270
260
250
240
230
50
40
30
20
10
0
-10
-20
-30
-40
Figure 7.1 Environmental conditions that influence microbial adaptations
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Microbial Nutrition
• 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
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Chemical Analysis of Cell Contents
• 70% water
• Proteins
• 96% of cell is composed of 6 elements: – Carbon
– Hydrogen
– Oxygen
– Phosphorous
– Sulfur
– Nitrogen
• Done to understand the cell’s nutritional make-up
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Forms, Sources, and Functions of Essential Nutrients
• Carbon-based Nutritional Types
• 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
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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
8
Classification of 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
9
Nutritional Categories
Autotrophs and Their Energy Sources
• Photoautotrophs – energy source is sunlight – Oxygenic photosynthesis
– Anoxygenic photosynthesis
• Chemoautotrophs (lithoautotrophs) – energy source is
inorganic substances, such as hydrogen sulfide
• Methanogens, a kind of chemoautotroph, produce
methane gas under anaerobic conditions
10
© Kathy Park Talaro
Figure 7.2 Methanococcus
jannaschii
Heterotrophs and Their Energy Sources
• 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 11
(b)
(c)
(d)
Figure 7.3 Extracellular Digestion in Bacteria and Fungi
(a) Walled cell is a barrier.
Enzymes are transported outside the wall.
Enzymes hydrolyze the bonds on nutrients.
Smaller molecules are transported across the
wall and cell membrane into the cytoplasm.
Organic debris
Enzymes
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7.3 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
13
Adaptations to Temperature
Three 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
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Three 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
-15 -10 -5 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90
Temperature °C
Psychrophile
Mesophile
Thermophile
Optimum
Maximum Minimum
Figure 7.9
Ecological groups
by temperature of
adaptation
15
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
16
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
Culturing by Oxygen Requirement
© Terese M. Barta, Ph.D.
Photo by Keith Weller, USDA/ARS
Figure 7.12 Growth medium to determine oxygen
requirements. +O2 -O2 usage by bacteria
Figure 7.11 Culturing anaerobic bacteria
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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
Courtesy and © Becton, Dickinson and Company
Figure 7.11b. a CO2
incubator
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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
20
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
21
Miscellaneous Environmental Factors
• Barophiles – can survive under extreme
pressure and will rupture if exposed to normal
atmospheric pressure
22
7.4 Ecological Associations Among Microorganisms
Microbial Associations
Symbiotic
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.
Nonsymbiotic
23
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
Haemophilus
satellite
colonies
Staphylococcus
aureus
growth
© Science VU/Fred Marsik/Visuals Unlimited
Courtesy Arthur Hauck (Germany)
Figure 7.13 Satellitism, a type of commensalism
24
Interrelationships Between Microbes and Humans
• Human body is a rich habitat for symbiotic
bacteria, fungi, and a few protozoa - normal
microbial flora
• Types of relationships: commensal, parasitic,
and synergistic relationships
25
Microbial Biofilms – A Meeting Ground
• 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
26
Figure 7.14 Biofilm Formation and Quorum Sensing
Chromosome
Matrix
Quorum-dependent
proteins
Inducer
molecule
Free-swimming cells settle on a surface and remain there.
Cells synthesize a sticky matrix that holds them tightly to
the substrate.
When biofilm grows to a certain density (quorum), the cells release
inducer molecules that can coordinate a response.
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.
Cells secrete their enzymes in unison to digest food particles.
1
1
2
2
3
3
4
4
5
5
27
7.5 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
28
The Basis of Population Growth: Binary Fission
Cell wall Ribsomes
A young cell at early phase of cycle 1
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.
2
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.
3
The septum is synthesized completely
through the cell center, and the cell
membrane patches itself so that there
are two separate cell chambers.
4
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.
5
Cell membrane Chromosome 1 Chromosome 2
Figure 7.15
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The 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
(a)
Number
of cells
Number of
generations
2 4 8 16
Exponential
value
1
1 3 4
21 22 23 24 25
32
5 2
(21) (22) (222) (2222) (22222)
(b)
( ) ( ) Number
of cells
Log of
number
of cells
using the
power
of 2
Time
0
9
10
11
*12
0
500
1000
1500
2000
2500
3000
3500
4000
4500* Figure 7.16
Determinants of Population Growth The Viable Plate Count: Batch Culture Method
1
Samples taken at equally spaced intervals
60 min
0.1
ml
120 min 180 min 240 min 300 min 360 min 420 min 480 min 540 min 600 min
500 ml
(0.1 ml)
Flask inoculated
Sample is
diluted in
liquid agar
medium
and poured
or spread
over surface
of solidified
medium
Plates are
incubated,
colonies
are counted
*Only means that too few cells are present to be assayed.
1,150,000
<1*
<10,000
2
5,000
4
20,000
7
35,000
13
65,000
23
15,000
45
225,000
80
400,000
135
675,000
230
None
Total estimated
cell population
in flask
Number of
colonies (CFU)
per 0.1 ml
31
Figure 7.18 The Population Growth Curve
In laboratory studies, populations typically display a predictable pattern over time – growth curve
Stages in the normal growth curve:
1. Lag phase – “flat” period of adjustment, enlargement; little growth
5 0
10 15 20 25 30 35 40
2
3
4
5
6
7
8 9
10 Stationary phase
T otal cells in population, live and dead, at each phase
Few cells Live cells Dead cells (not part of count)
The final
outcome
varies with
the culture.
Hours
Lo
gri
thm
(10
n)
of
Via
ble
Cell
s
32
The Population Growth Curve Stages in the normal growth curve:
1. Lag phase
2. Exponential growth phase – a period of maximum growth will continue as long as cells have adequate nutrients and a favorable environment
5 0
10 15 20 25 30 35 40
2
3
4
5
6
7
8 9
10 Stationary phase
T otal cells in population, live and dead, at each phase
Few cells Live cells Dead cells (not part of count)
The final
outcome
varies with
the culture.
Hours
Lo
gri
thm
(10
n)
of
Via
ble
Cell
s
33
The Population Growth Curve Stages in the normal growth curve:
1. Lag phase
2. Exponential growth phase
3. Stationary phase – rate of cell growth equals rate of cell death caused by depleted nutrients and O2, excretion of organic acids and pollutants
5 0
10 15 20 25 30 35 40
2
3
4
5
6
7
8 9
10 Stationary phase
T otal cells in population, live and dead, at each phase
Few cells Live cells Dead cells (not part of count)
The final
outcome
varies with
the culture.
Hours
Lo
gri
thm
(10
n)
of
Via
ble
Cell
s
34
The Population Growth Curve Stages in the normal growth curve:
1. Lag phase
2. Exponential growth phase
3. Stationary phase
4. Death phase – as limiting factors intensify, cells die exponentially
5 0
10 15 20 25 30 35 40
2
3
4
5
6
7
8 9
10 Stationary phase
T otal cells in population, live and dead, at each phase
Few cells Live cells Dead cells (not part of count)
The final
outcome
varies with
the culture.
Hours
Lo
gri
thm
(10
n)
of
Via
ble
Cell
s
35
Other Methods of Analyzing Population Growth
• Turbidometry – most simple, use a spectrophotometer
• Degree of cloudiness, turbidity, reflects the relative population size
(1)
(2) (b)
Percent of light
transmitted
(a) © Kathy Park Talaro/Visuals Unlimited
Figure 7.19
T ~ A or T ~ A
