2010040145495125 by xiagong0815

VIEWS: 0 PAGES: 52

									PA RT II Microbial Nutrition,
    Growth, and Control


          Chapter5
   Microbial Nutrition
           5.   Microbial Nutrition

Outline:
           • Nutrient requirements
           • Nutritional types of microorganisms
           • Uptake of Nutrients by the Cell
           • Culture Medium
           • Isolation of Pure Cultures
                            Concepts
1. Microorganisms require about 10 elements in large quantities, in part
   because they are used to construct carbohydrates, lipids, proteins, and
   nucleic acids. Several other elements are needed in very small
   amounts and are parts of enzymes and cofactors.
2. All microorganisms can be placed in one of a few nutritional
   categories on the basis of their requirements for carbon, energy, and
   hydrogen atoms or electrons.
3. Nutrient molecules frequently cannot cross selectively permeable
   plasma membranes through passive diffusion. They must be
   transported by one of three major mechanisms involving the use of
   membrane carrier proteins. Eucaryotic microorganisms also employ
   endocytosis for nutrient uptake.
4. Culture media are needed to grow microorganisms in the laboratory
   and to carry out specialized procedures like microbial identification,
   water and food analysis, and the isolation of articular microorganisms.
   Many different media are available for these and other purposes.
5. Pure cultures can be obtained through the use of spread plates, streak
   plates, or pour plates and are required for the careful study of an
   individual microbial species.
                 Macronutrients
• 95% or more of cell dry weight is made up of a
  few major elements: carbon, oxygen, hydrogen,
  nitrogen, sulfur, phosphorus, potassium,
  calcium, magnesium and iron.
• The first six ( C, H, O, N, P and S) are
  components of carbonhadrates, lipids, proteins
  and nucleic acids
                  Trace Elements

Microbes require very small amounts of other mineral
elements, such as iron, copper, molybdenum, and zinc;
these are referred to as trace elements. Most are
essential for activity of certain enzymes, usually as
cofactors.
                   Growth Factors

(1)amino acids, (2) purines and pyrimidines, (3) vitamins


  Amino acids are needed for protein synthesis,
  purines and pyrimidines for nucleic acid synthesis.
  Vitamins are small organic molecules that usually
     make up all or part enzyme cofactors, and only
     very small amounts are required for growth.
       Nutritional types of microorganisms
                     Sources of energy,
Major nutritional    hydrogen/electrons,         Representative
type                 and carbon                  microorganisms
Photoautotroph       Light energy, inorganic     Algae, Purple and green
                     hydrogen/electron(H/e-)     bacteria, Cyanobacteria
(Photolithotroph)    donor, CO2 carbon source

Photoheterotroph     Light energy, inorganic     Purple nonsulfur bacteria,
                     H/e- donor,                 Green sulfur bacteria
(Photoorganotroph)
                     Organic carbon source
Chemoautotroph       Chemical energy source      Sulfur-oxdizing bacteria,
                     (inorganic), Inorganic H/e- Hydrogen bacteria,
(Chemolithotroph)    donor, CO2 carbon source Nitrifying bacteria

Chemoheterotroph     Chemical energy source      Most bacteria, fungi,
                     (organic), Organic H/e-     protozoa
(Chenoorganotroph)   donor, Organic carbon
                     source
 Photoautotroph:
     Algae, Cyanobacteria

     CO2 + H2O         Light + Chlorophyll
                                             (CH2O) +O2

 Purple and green bacteria

 CO2 + 2H2S         Light + bacteriochlorophyll
                                                  (CH2O) +
 H2O + 2S
 Photoheterotroph:
Purple nonsulfur bacteria (Rhodospirillum)
CO2 + 2CH3CHOHCH3                 Light + bacteriochlorophyll
                                                                (CH2O)
+ H2O + 2CH3COCH3
    Properties of microbial photosynthetic systems

Property           cyanobacteria   Green and            Purple nonsulfur
                                   purple bacteria      bacteria
Photo - pigment    Chlorophyll     Bcteriochlorophyll   Bcteriochlorophyll

O2 production      Yes             No                   No
Electron donors    H2O             H2, H2S, S           H2, H2S, S
Carbon source      CO2             CO2                  Organic / CO2
Primary products   ATP + NADPH     ATP                  ATP
of energy
conversion
 Chemoautotroph:

Bacteria                     Electron      Electron     Products
                             donor         acceptor
Alcaligens and               H2            O2           H2O
Pseudomonas sp.
Nitrobacter                  NO2-          O2           NO3- , H2O
Nitrosomonas                 NH4+          O2           NO2- , H2O
Desulfovibrio                H2            SO4 2-       H2O. H2S
Thiobacillus denitrificans
                             S0. H2S       NO3-         SO4 2- , N2
Thiobacillus ferrooxidans
                             Fe2+          O2           Fe3+ , H2O

   Nitrifying bacteria

   2 NH4+ + 3 O2                  2 NO2- + 2 H2O + 4 H+ + 132 Kcal
              Culture media

are needed to grow microorganisms in the
laboratory and to carry out specialized
procedures like microbial identification,
water and food analysis, and the isolation
of particular microorganisms. A wide
variety of media is available for these and
other purposes.
         Pure cultures

can be obtained through the use of
spread plates, streak plates, or pour
plates and are required for the careful
study of an individual microbial species.
              Uptake of nutrients


Nutrient molecules frequently cannot cross selectively
permeable plasma membranes through passive
diffusion and must be transported by one of three
major mechanisms involving the use of membrane
carrier proteins.
1, Phagocytosis – Protozoa
2, Permeability absorption – Most microorganisms



   •   passive transport , simple diffusion
   •   facilitated diffusion
   •   active transport
   •   group translocation
                    passive diffusion




A few substances, such as glycerol, can cross the plasma
membrane by passive diffusion. Passive diffusion is the
process in which molecules move from a region of higher
concentration to one of lower concentration as a result of
random thermal agitation.
                       Facilitated diffusion




The rate of diffusion across selectively permeable membranes
is greatly increased by the use of carrier proteins, sometimes
called permeases, which are embedded in the plasina
membrane. Since the diffusion process is aided by a carrier, it
is called facilitated diffusion. The rate of facilitated diffusion
increases with the concentratioti gradient much more rapidly
and at lower concentrations of the diffusing molecule than that
of passive diffusion
  Active transport

Active transport is the
transport of solute
molecules to higher
concentrations, or against a
concentration gradient,
with the use of metabolic
energy input.
Group translocation
1, Phagocytosis – Protozoa
2, Permeability absorption – Most microorganisms



   •   passive transport , simple diffusion
   •   facilitated diffusion
   •   active transport
   •   group translocation
               passive diffusion



A few substances, such as glycerol, can cross the
plasma membrane by passive diffusion. Passive
diffusion is the process in which molecules move
from a region of higher concentration to one of
lower concentration as a result of random
thermal agitation.
                       Facilitated diffusion




The rate of diffusion across selectively permeable membranes
is greatly increased by the use of carrier proteins, sometimes
called permeases, which are embedded in the plasina
membrane. Since the diffusion process is aided by a carrier, it
is called facilitated diffusion. The rate of facilitated diffusion
increases with the concentration gradient much more rapidly
and at lower concentrations of the diffusing molecule than that
of passive diffusion
A model of facilitated diffusion

The membrane carrier can change
conformation after binding an
external molecule and
subsequently release the molecule
on the cell interior. It then returns
to the outward oriented position
and is ready to bind another solute
molecule.

Because there is no energy input, molecules
will continue to enter only as long as their
concentration is greater on the outside.
  Active transport

Active transport is the
transport of solute
molecules to higher
concentrations, or against a
concentration gradient,
with the use of metabolic
energy input.
                 Group translocation


 The best-known group translocation system is the
 phosphoenolpyruvate: sugar phosphotransferase system
 (PTS), which transports a variety of sugars into procaryotic
 cells while Simultaneously phosphorylating them using
 phosphoenolpyruvate (PEP) as the phosphate donor.


PEP + sugar (outside)           pyruvate + sugar-P (inside)
The phosphoenolpyruvate: sugar phosphotransferase system of E.
coli. The following components are involved in the system:
phosphoenolpyruvate, PEP; enzyme 1, E I; the low molecular
weight heat-stable protein, HPr; enzyme 11, E II,- and enzyme III,
E III.
               Simple comparison of transport systems
Items              Passive          Facilitated   Active        Group
                   diffusion        diffusion     transport     translocation

                   Non              Yes           Yes           Yes
carrier proteins

transport speed    Slow             Rapid         Rapid         Rapid


against gradient Non                Non           Yes           Yes


                                    Specificity   Specificity   Specificity
transport          No specificity
molecules
metabolic          No need          Need          Need          Need
energy

Solutes            Not changed      Changed       Changed       Changed
molecules
Mode of action of antibacterial antibiotics
Symbiosis of peptidoglycan
                           Questions
1. Throughout history, spices have been used as preservatives and to
   cover up the smell/taste of food that is slightly spoiled. The
   success of some spices led to a magical, ritualized use of many of
   them and possession of spices was often limited to priests or other
   powerful members of the community. a. Choose a spice and trace
   its use geographically and historically. What is its common-day use
   today? b. Spices grow and tend to be used predominantly in
   warmer climates. Explain.
2. Design an experiment to determine whether an antimicrobial agent
   is acting as a cidal or static agent. How would you determine
   whether an agent is suitable for use as an antiseptic rather than as a
   disinfectant?
3. Suppose that you are testing the effectiveness of disinfectants with
   the phenol coefficient test and obtained the following results.
                 Chapter 6 Microbial growth


Outline

    • The Growth Curve
    • Cell life cycle
    • Measurement of Microbial Growth
    • Measurement of Cell Mass
    • Growth Yields and the Effects of a Limiting Nutrient
    • The Continuous Culture of Microorganisms
    • The Chemostat
    • The Influence of Environmental Factors on Growth
                        Concepts

1.    Growth is defined as an increase in cellular constituents
     and may result in an increase in an organism's size,
     population number, or both.
2. When microorganisms are grown in a closed system,
   population growth remains exponential for only a few
   generations and then enters a stationary phase due to
   factors like nutrient limitation and waste accumulation.
   If a population is cultured in an open system with
   continual nutrient addition and waste removal, the
   exponential phase can be maintained for long periods.
  3. A wide variety of techniques can be used to study
   microbial growth by following changes in the total cell
   number, the population of viable microorganisms, or the
   cell mass.
4. Water availability, pH, temperature, oxygen
    concentration, pressure, radiation, and a number of
    other environmental factors influence microbial growth.
    Yet many microorganisms, and particularly bacteria,
    have managed to adapt and flourish under
    environmental extremes that would destroy most
    organisms.
Growth definition:

Growth may be generally defined as a steady
increase in all of the chemical components of an
organism. Growth usually results in an increase
in the size of a cell and frequently results in cell
division
                 Cell life cycle in Eukaryotic cells

G1   Primary growth phase of the cell during which cell enlargement occurs, a
gap phase separating cell growth from replication of the genome

S    phase in which replication of the genome occurs

G2 Phase in which the cell prepares for separation of the replicated genomes,
this phase includes synthesis of microtubules and condensation of DNA to
form coherent chromosomes, a gap phase separating chromosome replication
from miosis.

M    phase called miosis during which the microtubular apparatus is associated
and subsequently used to pull apart the sister chromosomes.

    Eukaryotic cell:        G1         S         G2          M

    Prokaryotic cell:       G1          R              D
 Binary fision

Most bacterial cells reproduce asexually by binary fision, a
process in which a cell divides to produce two nearly equal-
sized progeny cells. Binary fision involves three processes:
Increase in cell size (cell elongation),
DNA replication
Cell division
           Growth curve of bacteria




1. Lag Phase
2. Exponential Phase
3. Stationary Phase
4. Death Phase
           Growth curve of bacteria




1. Lag Phase
2. Exponential Phase
3. Stationary Phase
4. Death Phase
                                      Stationary Phase



                  Logarithmic
                  growth phase                                          Death Phase




                Lag Phase



     (a)        Lag phase: cells begin to synthesize inducible enzymes and use stored food
    reserves.
•   (b)    Logarithmic growth phase: the rate of multiplication is constant.
•   (c)    Stationary phase: death rate is equal to rate of increase.
•   (d)    Death phase: cells begin to die at a more rapid rate than that of reproduction.
        generation time

   The time required for a cell to divide (and its
   population to double) is called the generation time.
   Suppose that a bacterial population increases from103 cells
   to 109 cells in 10 hours. Calculate the generation time.

                          Nt = No x 2n        G = t log2 / log Nt – log No
Number of cells




                           No = number of bacteria at beginning of time interval.
                           Nt = number of bacteria at end of any interval of time (t).
                           G = generation time
                           T = time , usually expressed in minutes
                           n = number of generation

                  Time
fermenter
Continuous culture
of microorganisms




 Chemostat




Chemostat used for continuous cultures. Rate of growth can be
controlled either by controlling the rate at which new medium
enters the growth chamber or by limiting a required growth
factor in the medium.
Effect of temperature on bacterial growth rate




Bacteria grow over a range of temperatures; they do not
reproduce below the minimum growth temperattire nor
above the maximum growth temperature. Within the
temperature growth range there is an optimum growth
temperature at which bacterial reproduction is fastest.
Enzymes exhibit a Q10 so that within a suitable
temperature range the rate of enzyme activity doubles for
every 10' C rise in temperature.
Microorganisms are classified as psychrophiles,
mesophiles.thermophiles, and extremethemophiles
based on their optimal growth temperature.
Effect of oxygen concentration – reduction potential


  Effect of oxygen concentration on the growth of various
  bacteria in tubes of solid medium
厌氧菌的培养
(a) Obligate aerobes-growth occurs only in the short
distance to which the oxygen diffuses into the medium.
(b) Facultative anaerobes growth is best near the surface,
where oxygen is available, but occurs throughout the tube.
(c) Obligate anaerobes-oxygen is toxic, and there is no
growth near the surface.
(d) Aerotolerant anaerobes-growth occurs evenly
throughout the tube but is not better at the surface because
the organisms do not use oxygen.
(e) Microaerophiles, aerobic organisms that do not tolerate
atmospheric concentrations of oxygen-growth occurs only
in a narrow band of optimal oxygen concentration.
Effect of pH value on microbial growth



Bacteria: Neutral condition
Fungi:    Acidic condition
Actinomycetes: Alkaline condition
                         Water activity

The water activity of a solution is 1/100 the relative
humidity of the solution (when expressed as a percent), or
it is equivalent to the ratio of the solution's vapor
pressure to that of pure water.

                   aw = P solution / P water

Approximate lower aw limits for microbial growth:
0.90 – 1.00 for most bacteria, most algae and some fungi as
Basidiomycetes,Mucor, Rhizopus.
0.75 for Halobacterium, Aspergillus…
0.60 for some saccharomyces species
                         Plasmolysis

If the concentration of solutes, such as sodium chloride, is
higher in the surrounding medium (hypertonic), then water
tends to leave the cell. The cell membrane shrinks away
from the cell wall (an action called plasmolysis), and cell
growth is inhibited.

           Normal cell           Plasmolyzed cell
        Control of microbial growth


Definitions:

Sterilization – the process of destroying all forms of
microbial life on an object or in a material.
Disinfection – the process of destroying vegetative
pathogens but not necessary endospores.
Antisepsis – chemical disinfection of skin, mucous
membranes or other living tissues

								
To top