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Microbial Nutrition,

Ecology, and Growth

Chapter 7

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Microbial Must Obtain Nutrients from

Environment

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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

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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)

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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

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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

(PO43-)

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

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Sulfur Sources

Widely distributed throughout the environment in

mineral form

Essential component of some vitamins

Amino acids- methionine and cysteine

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).

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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

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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

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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

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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

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Osmotic Relationships

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

Isotonic: The environment is equal in solute concentration to the cell’s internal environment

Hypotonic: The solute concentration of the external environment is lower than that of the cell’s internal environment

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

Osmotic Relationships: Osmosis and Cells

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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.

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

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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

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 microbe’s 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

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Temperature Optima

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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

Rate

of

Gro

wth

maximum minimum

Psychrophile

A microorganism that has an optimum temperature

below 15°C and is capable of growth at 0°C.

True psychrophiles are obligate with respect to cold

and cannot grow above 20°C.

Psychrotrophs or facultative psychrophiles- grow

slowly in cold but have an optimum temperature

above 20°C.

“Red Snow”-

Psychrophile

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Mesophile

An organism that grows at intermediate

temperatures

Optimum growth temperature of most: 20°C

to 40°C

Temperate, subtropical, and tropical regions

Most human pathogens have optima between

30°C and 40°C

Thermophile

A microbe that grows optimally at temperatures

greater than 45°C

Vary in heat requirements

General range of growth of 45°C to 80°C

Hyperthermophiles- grow between 80°C and

120°C

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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

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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

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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

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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

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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

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Biofilms

Estimated to contribute to

80% of chronic infections

Resistant to most

antibiotic treatments

Mixed communities of

organisms

Quorum sensing

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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