Foundations in Microbiology

Chapter

7

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Fifth Edition

Talaro

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Elements of Microbial Nutrition, Ecology and Growth

Chapter 7

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Microbial nutrition

• Macronutrients – required in large quantities; play principal roles in cell structure & metabolism – proteins, carbohydrates

• Micronutrients or trace elements – required in small amounts; involved in enzyme function & maintenance of protein structure– manganese, zinc, nickel

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Nutrients

• 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

• Organic nutrients- contain carbon and hydrogen atoms and are usually the products of living things– methane (CH4), carbohydrates, lipids, proteins, and nucleic

acids

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Chemical composition of cytoplasm

• 70% water

• proteins

• 96% of cell is composed of 6 elements– Carbon– Hydrogen– Oxygen– Phosphorous– Sulfur

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Obtaining Carbon

• Heterotroph – an organism that 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 dependent on other living things

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Nitrogen

• Main reservoir is nitrogen gas (N2)• 79% of earth’s atmosphere is N2

• Nitrogen is part of the structure of proteins, DNA, RNA & ATP – these are the primary source of N for heterotrophs

• Some bacteria & algae use inorganic N nutrients (NO3

-, NO2-, or NH3)

• Some bacteria can fix N2

• Regardless of how N enters the cell, it must be converted to NH3, the only form that can be combined with carbon to synthesis amino acids, etc.

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Oxygen

• major component of carbohydrates, lipids and proteins

• plays an important role in structural & enzymatic functions of cell

• component of inorganic salts (sulfates, phosphates, nitrates) & water

• O2 makes up 20% of atmosphere

• essential to metabolism of many organisms

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Hydrogen

• major element in all organic compounds & several inorganic ones (water, salts & gases)

• gases are produced & used by microbes

• roles of hydrogen– maintaining pH– forming H bonds between molecules– serving as the source of free energy in oxidation-

reduction reactions of respiration

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Phosphorous

• main inorganic source is phosphate (PO4-3)

derived from phosphoric acid (H3PO4) found in rocks & oceanic mineral deposits

• key component of nucleic acids, essential to genetics

• serves in energy transfers (ATP)

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Sulfur

• widely distributed in environment, rocks, sediments contain sulfate, sulfides, hydrogen sulfide gas and sulfur

• essential component of some vitamins and the amino acids: methionine & cysteine

• contributes to stability of proteins by forming disulfide bonds

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Important mineral ions

• Potassium

• Sodium

• Calcium

• Magnesium

• Iron

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Growth factors

• organic compounds that cannot be synthesized by an organism & must be provided as a nutrient– essential amino acids, vitamins

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Carbon source

Energy source

photoautotrophs CO2 sunlight

chemoautotrophs CO2 Simple inorganic chemicals

photoheterotrophs organic sunlight

chemoheterotrophs organic Metabolizing organic cpds

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• Saprobes – decompose dead organisms, recycle elements, release enzymes to digest materials

• Parasites – utilize tissues and fluids of a living host and cause harm

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saprobes

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Transport mechanisms• Passive transport –do not require energy, substances

exist in a gradient and move from areas of higher concentration towards areas of lower concentration– Diffusion– Osmosis - water– Facilitated diffusion – requires a carrier

• Active transport – require energy and carrier proteins, gradient independent– Carrier-mediated active transport– Group translocation – transported molecule

chemically altered– Bulk transport – endocytosis, exocytosis, pinocytosis

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diffusion

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osmosis

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passive transport

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Active transport

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Bulk transport

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Environmental influences on microbial growth

• temperature

• oxygen requirements

• pH

• electromagnetic radiation

• barometric pressure

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3 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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3 temperature adaptation groups

1. Psychrophiles – optimum temperature below 15oC, capable of growth at 0oC

2. Mesophiles – optimum temperature 20o-40oC, most human pathogens

3. Thermophiles – optimum temperature greater than 45oC

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3 temperature adaptation groups

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Oxygen requirements

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Microbial associations

• Symbiotic – organisms live in close nutritional relationships; required by one or both members– Mutualism – obligatory, dependent; both

members benefit– Commensalism – commensal member benefits,

other member not harmed– Parasitism – parasite is dependent and benefits;

host is harmed

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Microbial associations

• Non-symbiotic – organisms are free-living; relationships not required for survival– Synergism – members cooperate and share

nutrients– Antagonism – some member are inhibited or

destroyed by others

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Binary Fission

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Population growth

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Growth curve

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Growth curve1. Lag phase – “flat” period of adjustment, enlargement;

little growth

2. Exponential growth phase – a period of maximum growth will continue as long as cells have adequate nutrients & a favorable environment

3. Stationary phase – rate of cell growth equals rate of cell death cause by depleted nutrients & O2, excretion of organic acids & pollutants

4. Death phase – as limiting factors intensify, cells die exponentially in their own wastes

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Turbidity

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Direct microscopic count

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Electronic counting