Microbial Nutrition, Ecology, and Growth

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Microbial Nutrition, Ecology, and Growth
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Microbial Nutrition

• Nutrition a process by which chemical
  substances (nutrients) are acquired from the
  environment and used in cellular activities
• All living things require a source of elements
  such as C, H, O, P, K, N, S, Ca, Fe, Na, Cl, Mg-
  but the relative amounts vary depending on the
  microbe
• Essential Nutrient any substances that must be
  provided to an organism
• Macronutrients Required in relatively large
  quantities, play principal roles in cell
  structure and metabolism (ex. C, H, O)
• Micronutrients aka trace elements, present in
  smaller amounts and involved in enzyme function
  and maintenance of protein structure (ex. Mn, Zn,
  Ni)

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Microbial Nutrition contd

• 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

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Chemical Analysis of Microbial Cytoplasm
Nutritional requirements of bacteria determined
by the cells elemental composition.
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Major elements, their sources and functions in
bacterial cells.
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Essential Nutrients

• Carbon
• Nitrogen
• Oxygen
• Hydrogen
• Phosphorus
• Sulfur

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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 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)

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Oxygen Sources

• O is a major component of organic compounds
  (carbohydrates, lipids, nucleic acids and
  proteins)
• Also a common component of inorganic salts
• O2 makes up 20 of the atmosphere

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Hydrogen Sources

• H 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

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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
• Sulfur-containing amino acids- methionine and
  cysteine (disulfide bridges shape protein
  structure)

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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
  (cellular respiration)

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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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How Microbes Feed Nutritional Types
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Main Determinants of Nutritional Type

• Sources of carbon and energy
• Phototrophs- Microbes that photosynthesize
• Chemotrophs- Microbes that gain energy from
  chemical compounds

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Autotrophs and Their Energy Sources

• Photoautotrophs
• Photosynthetic
• Form the basis for most food webs
• Chemoautotrophs
• Chemoorganic autotrophs- use organic compounds
  for energy and inorganic compounds as a carbon
  source
• Lithoautotrophs- rely totally on inorganic
  minerals
• Methanogens- produce methane from hydrogen gas
  and carbon dioxide
• Archae
• Some live in extreme habitats

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Heterotrophs and Their Energy Sources

• Majority are chemoheterotrophs that derive both
  carbon and energy from organic compounds
• Saprobes
• Free-living microorganisms
• Feed primarily on organic detritus from dead
  organisms
• 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
• Facultative parasite- when a saprobe infects a
  host, usually when the host is compromised
  (opportunistic pathogen)

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Figure 7.2
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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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Transport Mechanisms for Nutrient Absorption

• Cells must take nutrients in and transport waste
  out
• Transport occurs across the cell membrane, even
  in organisms with cell walls
• Transport may be
• - active(energy dependent)
• ex. Carrier
  mediated active transport,
• group
  translocation,
• endocytosis
• - passive (energy
  independent)
• osmosis, simple
  diffusion, facilitated diffusion

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The Movement of Water Osmosis

• Osmosis Diffusion of water through a
  selectively permeable membrane
• The membrane is selectively permeable- having
  passageways that allow free diffusion of water
  but can block certain other dissolved molecules
  (solutes)
• When the membrane is between solutions of
  differing concentrations and the 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

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Osmotic Relationships

• The osmotic relationship between cells and their
  environment is determined by the 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
• Said to have high osmotic pressure

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Adaptations to Osmotic Variations in the
Environment

• Example fresh pond water- hypotonic conditions
• Bacteria- cell wall protects them from bursting
• Example high-salt environment- hypertonic
  conditions
• Halobacteria living in the Great Salt Lake-
  absorb salt to make their cells isotonic with the
  environment

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The Movement of Molecules Diffusion and
Transport

• Diffusion When atoms or molecules move in a
  gradient from an area of higher density or
  concentration to an area of lower density or
  concentration
• Diffusion of molecules across the cell membrane
  is largely determined by the concentration
  gradient and permeability of the substance
• Simple or passive diffusion is limited to small
  nonpolar molecules or lipid soluble molecules

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Facilitated Diffusion

• Utilizes a carrier protein that binds a specific
  substance, changes the conformation of the
  carrier protein, and the substance is moved
  across the membrane
• Once the substance is transported, the carrier
  protein resumes its original shape
• Carrier proteins exhibit specificity
• Saturation The rate of a substance is limited
  by the number of binding sites on the transport
  proteins

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Figure 7.6
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Active Transport

• Nutrients are transported against the diffusion
  gradient or in the same direction as the natural
  gradient but at a rate faster than by diffusion
  alone
• Requires the presence of specific membrane
  proteins (permeases and pumps)
• Requires the expenditure of energy
• Items that require active transport
• monosaccharides, amino acids,
  organic acids,
• phosphates, and metal ions

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Active transport contd

• 1. Carrier mediated (Specialized pumps)- an
  important type of active transport
• 2. Group translocation couples the transport of
  a nutrient with its conversion to a substance
  that is immediately useful inside the cell
• 3. Endocytosis A form of active transport.
  Transporting large molecules, particles, lipids,
  or other cells
• Ex. Phagocytosis- amoebas
  and certain white
• blood cells
  ingesting whole cells or large
• solid matter

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a) Carrier mediated active transport
b) Group translocation
c) Endocytosis
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Environmental Factors that Influence Microbes

• Temperature Adaptations
• Microbial cells cannot control their temperature,
  so they assume the ambient temperature of their
  natural habitat
• The range of temperatures for the growth of a
  given microbial species can be defined by three
  cardinal thermal points
• 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 (psychrophile), moderate (mesophile), or hot
  (thermophile) temperature range

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Figure 7.8
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Psychrophile

• A microorganism that has an optimum temperature
  below 15C and is capable of growth at 0C.
• Obligate psychrophiles -cannot grow above 20C.
• Psychrotrophs or facultative psychrophiles- grow
  slowly in cold but have an optimum temperature
  above 20C.

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Psychrophilic Chlamydomonas nivalis survives in
snow
Microscopc view of snow alga
Figure 7.9
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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

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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
  (Archae bacteria)

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Gas Requirements

• 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 toxic super oxides
• Detoxified by enzymes (found in all aerobic
  organisms)
• Superoxide dismutase
• Catalase

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Several General Categories of Oxygen Requirements

• Aerobes
• 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
• Anaerobe
• lacks the metabolic enzyme systems for using
  oxygen in respiration
• - Strict, or obligate, anaerobes also
  lack the enzymes for processing toxic oxygen
• and 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

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Culturing anaerobes
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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 on growth

• Majority of organisms live or grow in habitats
  between pH 6 and 8
• Three cardinal points for pH
• Minimum
• Maximum
• Optimum (may vary)
• Acidophiles - Optimum pH lt 7
• Neutrophiles- Optimum pH 7
• Alkalinophiles- Optimum pH gt 7

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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

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Symbiosis

• A general term used to denote a situation in
  which two organisms live together in a close
  partnership
• Members are termed symbionts
• Three main types of symbionts
• 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
Figure 7.12
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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

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The Study of Microbial Growth

• Growth takes place on two levels
• Cell synthesizes new cell components and
  increases in size (cell growth)
• The number of cells in the population increases
• (population growth)
• The Basis of Population Growth Binary Fission

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Figure 7.13
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Figure 7.14
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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
• As long as the environment is favorable, the
  doubling effect continues at a constant rate
• 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

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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

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Stages in the Normal Growth Curve

• Data from an entire growth period typically
  produce a curve with a series of phases
• Lag Phase
• Exponential Growth Phase
• Stationary Growth Phase
• Death Phase

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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

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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

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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

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Death Phase

• The curve dips downward
• Cells begin to die at an exponential rate

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Figure 7.15
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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