Microbial

Nutrition,

Ecology, and

Growth

Chapter 7

Copyright The McGraw-Hill Companies, Inc) Permission required for reproduction or display.

To run the animations you must be in Slideshow View. Use the

buttons on the animation to play, pause, and turn audio/text on or

off. Please note: once you have used any of the animation

functions (such as Play or Pause), you must first click in the white

background before you advance the next slide.

Microbial Must Obtain Nutrients

from Environment

7.1 Microbial Nutrition

All living things require a source of elements

Essential Nutrient: any substances that must be provided to an organism

Nutrients are processed and transformed into the chemicals of the cell after absorption

Can also categorize nutrients according to C content

Inorganic nutrients: A combination of atoms other than C and H

Organic nutrients: Contain C and H, usually the products of living things

Chemical Analysis of Microbial

Cytoplasm

Sources of Essential Nutrients

Carbon sources

Nitrogen sources

Oxygen sources

Hydrogen sources

Phosphorus sources

Sulfur sources

Others

Carbon Sources

The majority of C compounds involved in normal structure and metabolism of all cells are organic

Heterotroph: Must obtain C in organic form (nutritionally dependent on other living things)

Autotroph: (self-feeder) Uses inorganic CO2 as its carbon source (not nutritionally dependent on other living things)

Nitrogen Sources

Main reservoir- N2

Primary nitrogen source for heterotrophs- proteins, DNA, RNA

Some bacteria and algae utilize inorganic nitrogenous nutrients

Small number can transform N2 into usable compounds through nitrogen fixation

Regardless of the initial form, must be converted to NH3 (the only form that can be directly combined with C to synthesize amino acids and other compounds)

Oxygen Sources

Oxygen is a major component of organic compounds

Also a common component of inorganic salts

O2 makes up 20% of the atmosphere

Hydrogen Sources

Hydrogen is a major element in all organic and several inorganic compounds

Performs overlapping roles in the biochemistry of cells:

Maintaining pH

Forming hydrogen bonds between molecules

Serving as the source of free energy in oxidation-reduction reactions of respiration

Phosphorus (Phosphate) Sources

Main inorganic source of phosphorus is phosphate (PO4

3-)

Derived from phosphoric acid

Found in rocks and oceanic mineral deposits

Key component in nucleic acids

Also found in ATP

Phospholipids in cell membranes and coenzymes

Sulfur Sources

Widely distributed throughout the environment in mineral form

Essential component of some vitamins

Amino acids- methionine and cysteine

Other Nutrients Important in

Microbial Metabolism Potassium- protein synthesis and membrane function

Sodium- certain types of cell transport

Calcium- stabilizer of cell walls and endospores

Magnesium- component of chlorophyll and stabilizer of membranes and ribosomes

Iron- important component of cytochrome proteins

Zinc- essential regulatory element for eukaryotic genetics, and binding factors for enzymes

Cooper, cobalt, nickel, molybdenum, manganese, silicon, iodine, and boron- needed in small amounts by some microbes but not others

Growth Factors: Essential Organic

Nutrients

Growth factor: An organic compound such as an amino acid, nitrogenous base, or vitamin that

cannot be synthesized by an organism and must

be provided as a nutrient.

For example, many cells cannot synthesize all 20 amino acids so they must obtain them from food

(essential amino acids).

Microbial Nutritional Strategies

Carbon source:

Autotroph: self-feeders use carbon dioxide

Heterotroph: other-feeders use organic carbon

Energy source:

Chemotroph: use organic molecules

Phototroph: use light

Lithotroph: use inorganic molecules like H2S

Every combination is possible and does exist

Nutritional Categories

Saprobes

Free-living microorganisms

Decomposers of plant litter, animal matter, and dead microbes

Most have rigid cell wall, so they release enzymes to the extracellular environment and digest food particles into smaller molecules

Obligate saprobes- exist strictly on dead organic matter in soil and water

Other Chemoheterotrophs

Parasites

Derive nutrients from the cells or tissues of a host

Also called pathogens because they cause damage to tissues or even death

Ectoparasites- live on the body

Endoparasites- live in organs and tissues

Intracellular parasites- live within cells

Obligate parasites- unable to grow outside of a living host

Nutrient Transport

Most nutrients are polar

Do not cross the membrane alone

Requires a carrier

Need to concentrate essential nutrients

Requires energy

The Movement of Molecules:

Diffusion

Diffusion: When atoms or molecules move in a gradient from an area of higher concentration to an area of lower concentration

Will eventually evenly distribute the molecules

Simple or passive diffusion is limited to small nonpolar molecules or lipid soluble molecules

The Movement of Water: Osmosis

Osmosis: Diffusion of water through a selectively permeable membrane

Membrane: is selectively permeable; allows free diffusion of water but can block certain other dissolved molecules

When solute is not diffusible, water will diffuse at a fast rate from the side that has more water to the side that has less water.

Osmosis

How Osmosis Works

Please note that due to differing

operating systems, some animations

will not appear until the presentation is

viewed in Presentation Mode (Slide

Show view). You may see blank slides

in the Normal or Slide Sorter views. All animations will appear after viewing

in Presentation Mode and playing each

animation. Most animations will require

the latest version of the Flash Player,

which is available at

http://get.adobe.com/flashplayer.

Osmotic Relationships

Relative concentrations of the solutions on either side of the cell membrane

Isotonic: The environment is equal in solute concentration to the cells internal environment

No net change in cell volume

Generally the most stable environment for cells

Hypotonic: The solute concentration of the external environment is lower than that of the cells internal environment

Net direction of osmosis is from the hypotonic solution into the cell

Cells without cell walls swell and can burst

Hypertonic: The environment has a higher solute concentration than the cytoplasm

Will force water to diffuse out of a cell

Cell will shrink

Osmosis and Cells

Adaptations to Osmotic Variations in the

Environment

Example: fresh pond water- hypotonic conditions

Bacteria- cell wall protects them from bursting

Amoeba- a water vacuole moves excess water out of the cell

Example: high-salt environment- hypertonic conditions

Halobacteria living in the Great Salt Lake- absorb salt to make their cells isotonic with the

environment

Concept Check

What are the osmotic conditions in jellies and jams

compared to the bacterial cytoplasm?

A. Jelly is hypertonic to the cytoplasm

B. Jelly is isotonic to the cytoplasm

C. Jelly is hypotonic to the cytoplasm

Facilitated Diffusion

Used to transport hydrophilic molecules

Protein carrier

No energy required

Movement down the concentration

gradient

Specificity

Saturation

Extracellular

High

Facilitated Diffusion

Intracellular

Co

nc

en

tra

tio

n

Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Facilitated Diffusion

Please note that due to differing

operating systems, some animations

will not appear until the presentation is

viewed in Presentation Mode (Slide

Show view). You may see blank slides

in the Normal or Slide Sorter views. All animations will appear after viewing

in Presentation Mode and playing each

animation. Most animations will require

the latest version of the Flash Player,

which is available at

http://get.adobe.com/flashplayer.

Active Transport

Protein carrier and energy required

Movement against the gradient Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Membrane Membrane Membrane

Protein

Protein

(a)

Extracellular Intracellular Extracellular

Protein

Protein

Intracellular Extracellular Intracellular

Protein

Protein

Protein

Protein

Protein

Protein

Intracellular Extracellular

(b)

Intracellular Extracellular

Membrane Membrane

Active Transport

Please note that due to differing

operating systems, some animations

will not appear until the presentation is

viewed in Presentation Mode (Slide

Show view). You may see blank slides

in the Normal or Slide Sorter views. All animations will appear after viewing

in Presentation Mode and playing each

animation. Most animations will require

the latest version of the Flash Player,

which is available at

http://get.adobe.com/flashplayer.

Endocytosis and Exocytosis

Endocytosis- particles are engulfed

Phagocytosis- process carried out by white blood cells to engulf cells or particles

Pinocytosis- liquids entering the cell

Exocytosis: package and release of substances from a cell

Endo- and Exocytosis

Please note that due to differing

operating systems, some animations

will not appear until the presentation is

viewed in Presentation Mode (Slide

Show view). You may see blank slides

in the Normal or Slide Sorter views. All animations will appear after viewing

in Presentation Mode and playing each

animation. Most animations will require

the latest version of the Flash Player,

which is available at

http://get.adobe.com/flashplayer.

Concept Check

Facilitated diffusion ____________.

A. requires a carrier and energy

B. requires a carrier by not energy

C. requires neither a carrier nor energy

D. modifies the substrate during transport

7.2 Environmental Factors that Influence

Microbes - Temperature

The range of temperatures for the growth of a given microbial species can be expressed as three cardinal temperatures:

Minimum temperature: the lowest temperature that permits a microbes continued growth and metabolism

Maximum temperature: The highest temperature at which growth and metabolism can proceed

Optimum temperature: A small range, intermediate between the minimum and maximum, which promotes the fast rate of growth and metabolism

Some microbes have a narrow cardinal range while others have a broad one

Another way to express temperature adaptation- to describe whether an organism grows optimally in a cold, moderate, or hot temperature range

Temperature Optima Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

5

Psychrophile

Psychrotroph

Thermophile

Mesophile

Extremethermophile

Temperature C

-15 -10 -5 0 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 1051 1011 5120 1251 30

Optimum

Ra

te o

f G

row

th

maximum minimum

Psychrophile

A microorganism that has an optimum temperature below 15C and is capable of growth at 0C.

True psychrophiles are obligate with respect to cold and cannot grow above 20C.

Psychrotrophs or facultative psychrophiles- grow slowly in cold but have an optimum temperature

above 20C.

Red Snow- Psychrophile

Mesophile

An organism that grows at intermediate temperatures

Optimum growth temperature of most: 20C to 40C

Temperate, subtropical, and tropical regions

Most human pathogens have optima between 30C and 40C

Thermophile

A microbe that grows optimally at temperatures greater than 45C

Vary in heat requirements

General range of growth of 45C to 80C

Hyperthermophiles- grow between 80C and 120C

Environmental Factors- Gas

Atmospheric gases that most influence microbial growth- O2 and CO2

Oxygen gas has the greatest impact on microbial growth

As oxygen enters into cellular reactions, it is transformed into several toxic products

Most cells have developed enzymes that go about scavenging and neutralizing these chemicals

Superoxide dismutase

Catalase

Several General Categories of Oxygen

Requirements

Aerobe: can use gaseous oxygen in its metabolism and possesses the enzymes needed to process toxic oxygen products

Obligate aerobe: cannot grow without oxygen

Facultative anaerobe: an aerobe that does not require oxygen for its metabolism and is capable of growth in the absence of it

Microaerophile: does not grow at normal atmospheric concentrations of oxygen but requires a small amount of it in metabolism

Gas Requirements

Anaerobe: lacks the metabolic enzyme systems for using oxygen in respiration

Strict or obligate anaerobes: cannot tolerate any free oxygen in the immediate environment and will die if exposed to it.

Aerotolerant anaerobes: do not utilize oxygen but can survive and grow to a limited extent in its presence

Carbon Dioxide

All microbes require some carbon dioxide

in their metabolism

Capnophiles grow best at a higher CO2

tension than is

normally present in the

atmosphere

Effects of pH

Majority of organisms live or grow in habitats between pH 6 and 8

Acidophiles, Neutrophiles, Alkaliphiles

Obligate acidophiles

Euglena mutabilis- alga that grows between 0 and 1.0 pH

Thermoplasma- archae that lives in hot coal piles at a pH of 1 to 2, and would lyse if

exposed to pH 7

Osmotic Pressure

Most microbes live either under hypotonic or isotonic conditions

Osmophiles- live in habitats with a high solute concentration

Halophiles- prefer high concentrations of salt

Obligate halophiles- grow optimally in solutions of 25% NaCl but require at least 9% NaCl for

growth

Miscellaneous Environmental

Factors Nonphotosynthetic microbes tend to be damaged by

the toxic oxygen products produced by contact with light

Other types of radiation that can damage microbes are ultraviolet and ionizing rays

Barophiles: deep-sea microbes that exist under hydrostatic pressures ranging from a few times to over 1,000 times the pressure of the atmosphere

All cells require water- only dormant, dehydrated cells tolerate extreme drying

Concept Check

What sort of microbe only grows in the presence of

oxygen?

A. Anaerobe

B. Facultative anaerobe

C. Aerobe

D. Halophile

Ecological Associations Among

Microorganisms

Most microbes live in shared habitats.

Interactions can have beneficial, harmful, or no particular effects on the organisms involved.

They can be obligatory or nonobligatory to the members.

They often involve nutritional interactions.

Symbiosis

A general term used to denote a situation in which two organisms live together in a close partnership

Mutualism: when organisms live in an obligatory but mutually beneficial relationship

Commensalism: the member called the commensal receives benefits, while its coinhabitant is neither harmed nor benefited

Satellitism: when one member provides nutritional or protective factors needed by the other

Parasitism: a relationship in which the host organism provides the parasitic microbe with nutrients and a habitat

Satellitism

Nonsymbiotic Relationships

Synergism

an interrelationship between two or more free-living organisms that benefits them but is not necessary for their survival

Antagonism

an association between free-living species that arises when members of a community compete

Biofilms

Estimated to contribute to 80% of chronic

infections

Resistant to most antibiotic treatments

Mixed communities of organisms

Quorum sensing

Interrelationships Between microbes

and Humans

Normal microbiotia: microbes that normally live on the skin, in the alimentary tract, and in other

sites in humans

Can be commensal, parasitic, and synergistic relationships

7.3 The Study of Microbial Growth

Growth takes place on two levels

Cell synthesizes new cell components and increases in size

The numger of cells in the population increases

The Basis of Population Growth: Binary Fission

Binary Fission

Asexual process

Within 24 hours, one cell can result in

4.7 x 1021 cells

5,100 tons

Ribosomes

1

2

3

4

5

Cell wall

Cell membrane

Chromosome 1

Chromosome 2

When septum is

complete, cells

are considered

divided. Some

species will

separate completely

as shown here, while

others remain attached, forming chains or doublets, for example.

Septum formation

begins.

Protein band forms in

center of cell.

Chromosome is

replicated and new

and old chromosomes

move to different sides

of cell.

A young cell.

Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Bacterial Cell Cycle

Please note that due to differing

operating systems, some animations

will not appear until the presentation is

viewed in Presentation Mode (Slide

Show view). You may see blank slides

in the Normal or Slide Sorter views. All animations will appear after viewing

in Presentation Mode and playing each

animation. Most animations will require

the latest version of the Flash Player,

which is available at

http://get.adobe.com/flashplayer.

The Rate of Population Growth

Generation or doubling time: The time required for a complete fission cycle

Each new fission cycle or generation increases the population by a factor of 2

The length of the generation time- a measure of the growth rate of an organism

Average generation time- 30 to 60 minutes under optimum conditions

Can be as short as 10 to 12 minutes

This growth pattern is termed exponential

Graphing Bacterial Growth

The data from growing bacterial populations are graphed by plotting the number of cells as a function of time

If plotted logarithmically- a straight line

If plotted arithmetically- a constantly curved slope

To calculate the size of a population over time: Nf = (Ni)2

n

Nf is the total number of cells in the population at some point in the growth phase

Ni is the starting number

N denotes the generation number

Population Growth

Concept Check

If you have 100 bacteria with a doubling time of 20

minutes in media, how many cells would there be

in two hours under optimal growth conditions?

A. 600

B. 1,200

C. 3,200

D. 6,400

The Population Growth Curve

A population of bacteria does not maintain its potential growth rate and double endlessly

A population displays a predictable pattern called a growth curve

The method to observe the population growth pattern:

Place a tiny number of cells in a sterile liquid medium

Incubate this culture over a period of several hours

Sampling the broth at regular intervals during incubation

Plating each sample onto solid media

Counting the number of colonies present after incubation

Stages in the Normal Growth Curve

Lag Phase

Exponential Growth Phase

Stationary Growth Phase

Death Phase

Growth Curve

Lag Phase

Relatively flat period

Newly inoculated cells require a period of adjustment, enlargement, and synthesis

The cells are not yet multiplying at their maximum rate

The population of cells is so sparse that the sampling misses them

Length of lag period varies from one population to another

Exponential Growth (Logarithmic or

log) Phase

When the growth curve increases geometrically

Cells reach the maximum rate of cell division

Will continue as long as cells have adequate nutrients and the environment is favorable

Stationary Growth Phase

The population enters a survival mode in which cells stop growing or grow slowly

The rate of cell inhibition or death balances out the rate of multiplication

Depleted nutrients and oxygen

Excretion of organic acids and other biochemical pollutants into the growth medium

Death Phase

The curve dips downward

Cells begin to die at an exponential rate

Potential Importance of the Growth Curve

Implications in microbial control, infection, food microbiology, and culture technology

Growth patterns in microorganisms can account for the stages of infection

Understanding the stages of cell growth is crucial for working with cultures

In some applications, closed batch culturing is inefficient, and instead, must use a chemostat or continuous culture system

Methods of Analyzing Population Growth

Turbidometry- a tube of clear nutrient solution becomes turbid as microbes grow in it

Use spectrophotometer

Enumeration of Bacteria

Direct or total cell count- counting the number of cells in a sample microscopically

Uses a special microscope slide (cytometer)

Used to estimate the total number of cells in a larger sample

Automated Counting

Coulter counter- electronically scans a culture as it passes through a tiny pipette

Flow cytometer also measures cell size and differentiates between live and dead cells

Real-time PCR allows scientists to quantify bacteria and other microorganisms that are

present in environmental or tissue samples

without isolating or culturing them

Automated Counting

Concept Check

Suppose that you have a suspension that contains

both live and dead microbial cells. What method

would be best to determine the number of live?

A. Cytometer

B. Coulter counter

C. Spectrophotometer

D. Colony counts after dilution