Elements of microbial nutrition ecology and growth chapter 7
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Elements of Microbial Nutrition, Ecology and Growth Chapter 7. Microbial nutrition. Macronutrients – required in large quantities; play principal roles in cell structure & metabolism proteins, carbohydrates

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Microbial nutrition
Microbial nutrition

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

    • proteins, carbohydrates

  • Micronutrientsor trace elements – required in small amounts; involved in enzyme function & maintenance of protein structure

    • manganese, zinc, nickel


  • 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

Chemical composition of cytoplasm
Chemical composition of cytoplasm

  • 70% water

  • proteins

  • 96% of cell is composed of 6 elements

    • Carbon

    • Hydrogen

    • Oxygen

    • Phosphorous

    • Sulfur

Obtaining carbon
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


  • 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.


  • 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


  • 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


  • 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)


  • 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

Important mineral ions
Important mineral ions

  • Potassium

  • Sodium

  • Calcium

  • Magnesium

  • Iron

Growth factors
Growth factors

  • organic compounds that cannot be synthesized by an organism & must be provided as a nutrient

    • essential amino acids, vitamins

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

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

Transport mechanisms
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

Environmental influences on microbial growth
Environmental influences on microbial growth

  • temperature

  • oxygen requirements

  • pH

  • electromagnetic radiation

  • barometric pressure

3 cardinal temperatures
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

3 temperature adaptation groups
3 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

Microbial associations
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

Microbial associations1
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

Growth curve1
Growth curve

  • Lag phase – “flat” period of adjustment, enlargement; little growth

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

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

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