Download Chapter 5 Lecture Notes: Microbial Nutrition

Chapter 5 Lecture Notes: Microbial Nutrition
I.
The common nutrient requirements
A. macroelements
1. major (g/L)
a) C, O, H, N, S, P
b) uses: part of proteins, nucleic acids, carbohydrates, and lipids
c) sources
(1) Carbon and oxygen frequently supplied together
(a) autotrophs = use CO2 as sole C source
(b) heterotrophs = use reduces, preformed organic
materials as C source
(2) Hydrogen
(a) lithotrophs = reduced inorganic molecules
(b) organotrophs = organic molecules
(3) Nitrogen
(a) can be part of the compounds that supply C
(b) amino acids
(c) ammonia
(d) nitrate
atmospheric nitrogen
(4) Phosphorus
(a) inorganic phosphate (PO34-)
(5) Sulfur
(a) sulfate
(b) amino acid cysteine
2. minor (mg/L)
a) K, Ca, Mg, Fe
b) uses: mostly cofactors for some enzymes and proteins
c) sources:
(1) K+, Ca2+, Mg2+ - mostly free ions and salts
(2) Fe
(a) free ions
(b) iron salts
(c) bound to compounds in animal hosts (i.e. hemoglobin,
lactoferrin)
B. microelements or trace elements (µg/L)
usually metals that serve structural and catalytic roles for some enzymes
C. Growth factors = Organic compounds that are required for growth because they can
not be synthesized by a particular organism and are part of essential cell components
1. Amino acids (for proteins)
2. Vitamins (small organic molecules used as cofactors in enzymes)
3. Purines and pyrimidines (for nucleic acid synthesis)
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II.
Energy requirements
A. phototrophs = use light energy
B. chemotrophs = oxidation of organic or inorganic compounds that are composed of the
elements described above for energy
III.
Nutritional types of organisms: For the most part, fall into the following classes:
Major nutritional types
Phototrophs
Lithoautotrophs
IV.
Chemotrophs
Organoheterotrophs
Lithoautotrophs
Organoheterotrophs
Uptake of nutrients by the cell
A. General concepts
1. Specific uptake of compounds
2. Uptake from a dilute solution/environment
3. Passage of compounds through outer membrane occurs via specific and "nonspecific" porins via simple diffusion (therefore, the concentration in the periplasm
must be less than that of the external environment – see simple diffusion below)
4. Passage of compounds through sieve-like periplasm without impediment
5. Passage of nutrients is through a selectively permeable plasma membrane by
the mechanisms described below:
B. Passive diffusion
1. Movement of molecules from an area of higher concentration to one of lower
concentration as a result of random thermal agitation
2. Rate of transport depends on the difference in solute [] between the inside and
outside of the cell (Fig. 5-1). Therefore, inefficient for most compounds because
difference in solute concentration is not high enough for reasonable transport rate.
3. Compounds transported
a) only those that can penetrate the inner and outer membranes
b) water, oxygen, carbon dioxide but not H+ or other ions
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C. Facilitated diffusion (Fig. 5-2)
1. Membrane spanning carrier proteins aid in diffusion off a compound across a
membrane
2. Carrier proteins are specific for the compound to be transported
3. Energy for the transport is derived from the concentration gradient (transport
is from high concentration to low concentration.
4. Used for glycerol transport in some prokaryotes.
5. Much more important in eukaryotes
D. Active transport (Fig. 5-3)
1. Energy-dependent transport of solutes from a lower concentration to a higher
one via specific membrane bound carrier proteins
2. Frequently, periplasmic binding proteins help deliver compound to the correct
plasma membrane transport protein
3. Types (based on energy course)
a) ATP-dependent (i.e. variety of sugars such as arabinose, maltose,,
amino acids)
b) proton motive force (PMF) dependent – force resulting from a
difference in pH ([H+]) and charge across the plasma membrane via the
electron transport chain
(1) primary active transport = metabolism-linked mechanism that
generates PMF
(2) secondary active transport = uses PMF from primary active
transport to transport a specific compound
(a) symport – transport of two compounds by one carrier
down the concentration gradient of one of the compounds
(i.e. lactose transport)
(b) antiport – transport of two compounds in opposite
directions by one carrier; Na/H antiporter sets up a Na
gradient that is used for symport of sugars and amino acids
E. Group translocation
1. Energy-dependent transport of a molecule into the cell while being chemically
altered
2. Energy in the form of reaction in which the compound is PO4
3. PTS system as an example (Fig. 5-4)
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F. Fe transport
1. Very scarce nutrient
a) in environment most iron is insoluble ferric hydroxide
b) in human host most iron is sequestered by the cells or bound to carrier
proteins called transferin and lactoferin
2. Mechanism to acquire Fe:
a) Secretion of siderophore, small molecules that have a high affinity for
iron (Fig. 5-4) à siderophores bring iron back to the cell à either entire
siderophore:Fe compex or just Fe is transported through outer membrane
via specific receptor, through periplasm via periplasmic binding proteins
à transport through plamsa membrane and into cytoplasm
b) hemolysins – lyse RBC for hemoglobin (which contains Fe) à
binding proteins for heme and/or hemoglobin in the outer membrane
c) Recepor proteins for lactoferrin and transferin in the outer membrane
G. Endocytosis in eukaryotes is main method for acquisition of nutrients (also by
receptor mediated diffusion)
V.
Culture media:
A. General considerations:
1. Must know about nutrition to design an appropriate medium for cultivation of
a particular microbe.
2. Different organisms grow best on different medias
3. Consider what the natural environment is
B. Types
1. Defined – all components are known
2. Complex (tryptic soy broth, nutrient broth)
a) contains unidentified components such as
(1) peptones: partial digestion of proteinaceous animal or plant
materials à C, N, energy, may be deficient in minerals/vitamins
(2) extracts: animal or plant tissues are extracted by boiling and
then dried à high content of vitamins, amino acids, nitrogen
bases, but may be deficient in heat labile substances
3. Selective media
a) media that favors growth of a particular class of organisms
b) i.e. MacConkey Agar has bile salts in it which inhibit gram positive
bacteria so gram negative bacteria are enriched for
4. Differential media
a) media that distinguishes between different groups of organisms based
on biological characteristics on that media
b) Example - blood agar differentiates between bacteria that do and do
not make a hemolysin that lyses red blood cells
c) Example - MacConkey agar because there is a dye in it that causes
bacteria that are fermenting a sugar to turn pink; those that are not are
white
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