Download Four most common elements utilized by all

Four most common elements utilized by all microorganisms are;
(1) Carbon (2) Hydrogen (3) Oxygen (4) Nitrogen
Note: organic compounds usually supply the hydrogen and the
oxygen to organism as well as carbon.
Nitrogen
Microorganims require large quantities of nitrogen for biosynthesis
 Inorganic sources of nitrogen can be utilized to produce organic
compounds
 Nitrogen can be assimilated (incorporated) into organic
molecules by different routes
Nitrogen Assimilation – during anaerobic respiration, molecules
other than oxygen are used as final electron acceptor in the electron
transport system. Assimilation is the process by which inorganic
compounds are reduced to serve this purpose during anaerobic
conditions. (inorganic nitrogen sources listed in decreasing
abundance)
1. N2 atmospheric nitrogen (78%) (Nitrogen fixation – the process
of reducing atmospheric nitrogen to ammonia)
a. few microorganisms can use nitrogen gas directly
b. Free-living bacteria (Azotobacter, Klebseilla, Clostridium)
c. Symbiotic bacteria (Rhizobium in association with
legumes)
d. Cyanobacteria (Anabaea)
e. Atmospheric nitrogen, or N2, is converted into two
molecules of ammonia under the action of the enzyme
nitrogenase
f. This is highly exergonic; utilizes 16 ATPs to make 2 NH3
g. N2 + H+ + e- + ATP →(nitrogenase)→ NH3
2. NO3 – nitrate
a. much more oxidized than the nitrogen in ammonia
b. must first be reduced to ammonia before conversion into
an organic form
c. can be formed by processes of nitrification (Nitrification is
the aerobic process by which ammonia is oxidized to
NO2, and then further oxidized to NO3.
d. Nitrosomonas and nitrosococcus are involved in the first
oxidative step
e. Nitrobacter (a chemolithoautotroph) is involved in the
second step.
f. This process can occur anaerobically in Nitrosomonas
eutropha but the products are nitrite and nitric oxide.
Note: the electron acceptor in this reaction is nitrogen
dioxide.
3. NH3 ammonia (ammonia incorporation/assimilation)
a. can be incorporated into organic material relatively easily
and directly
b. It is more reductive than other forms of inorganic nitrogen
(reduction is the process by which hydrogen atoms or
protons are added to a compound or molecule thus
reducing it oxidative state)
Phosphorus is also important for cell survival
1. Phosphorus is obtained from organic and inorganic sources
a. Inorganic sources can be utilized directly for cellular
material
b. Organic phosphate must be hydrolyzed at ester linkages
by phosphatases
2. Phosphorus important in formation of nucleic acids, proteins,
and phospholipids
3. it is an ATP coenzymes
The role of sulfur and sulfate Reduction
1. Inorganic sulfate (SO4) is utilized directly but first must be
activated
2. it’s reduced to H2S by utilizing 2 molecules of ATP and sulfate
reductase
3. this is a main constituent of amino acids, cysteine and
methionine, tRNA, coenzymes, and organic cofactor
[nonprotein substance needed by an enzyme for normal
activity] for an enzyme
4. organic sulfur can be added to cell directly by addition of
cysteine and/or methionine in growth media
 Other elements are required for growth and metabolism
but in much smaller amounts (K+, Mg, Ca++, Fe++)
 some organisms also require sodium or silicon but these
are a select few
Growth Factors – These compounds are essential to cell components
by cannot be synthesized by the organism requiring them. There are
three main classes of growth factors;
1. amino acids
2. purines & pyrimidines
3. vitamins
Amino Acids
 Synthesized by cell or provided by exogenous sources
(exogenous = derived or developed outside of the body;
originating externally)
 Needed for protein synthesis
Purines & pyrimidines
 Used for nucleic acids or coenzymes
Vitamins
 Small organic molecules used as enzyme cofactors
 Refer to table 5.3
3. Nitrogen source
Nitrogen is needed for the synthesis of such molecules as amino
acids, DNA, RNA and ATP. Depending on the organism, nitrogen,
nitrates, ammonia, or organic nitrogen compounds may be used as a
nitrogen source.
4. Minerals
a. sulfur
Sulfur is needed to synthesisize sulfur-containing amino acids and
certain vitamins. Depending on the organism, sulfates, hydrogen
sulfide, or sulfur-containing amino acids may be used as a sulfur
sorce.
b. phosphorus
Phosphorus is needed to synthesize phospholipids, DNA, RNA, and
ATP. Phosphate ions are the primary source of phosphorus.
c. potassium, magnesium, and calcium
These are required for certain enzymes to function as well as
additional functions.
d. iron
Iron is a part of certain enzymes.
e. trace elements
Trace elements are elements required in very minute amounts, and
like potassium, magnesium, calcium, and iron, they usually function
as cofactors in enzyme reactions. They include sodium, zinc,
copper,molybdenum, manganese, and cobalt ions. Cofactors usually
function as electron donors or electron acceptors during enzyme
reactions.
5. Water
6. Growth factors
Growth factors are organic compounds such as amino acids, purines,
pyrimidines, and vitamins that a cell must have for growth but cannot
synthesize itself. Organisms having complex nutritional requirements
and needing many growth factors are said to be fastidious.
7. Some Relationships Between Bacterial Growth and Pathogenicity
a. Ability to compete for limited nutrients
Often the ability to be pathogenic is directly related to the bacterium's
ability to compete successfully with host tissue and normal flora for
limited nutrients. One reason the generation time of bacteria growing
in the body is substantially slower than in lab culture is because
essential nutrients are limited.
To be pathogenic, a bacterium must be able to multiply in host tissue.
The more rapid the rate of replication, the more likely an infection
may be established. Pathogens, therefore, are able to compete
successfully for limited nutrients in the body.
Generally bacteria compete for nutrients by synthesizing specific
transport systems or cell wall components capable of binding limiting
substrates and transporting them into the cell.
For example, the body makes considerable metabolic adjustment
during infection to deprive microorganisms of iron. Iron is essential for
both bacterial growth and human cell growth. Bacteria synthesize iron
chelators (compounds capable of binding iron) called siderophores.
Many siderophores are excreted by the bacterium into the
environment, bind iron, and then re-enter the cell. Others are found
on the cell wall where they bind iron and transport it into the
bacterium. The body has iron chelators of its own (transferrin and
lactoferrin). The ability of bacterial iron chelators to compete
successfully with body iron chelators may be essential to pathogenic
bacteria. Some bacteria such as Neisseria gonorrhoeae, Neisseria
meningitidis, and Hemophilus influenzaea, however, have receptors
for human lactoferrin and transferrin and can utilize iron bound to
these compounds.
b. Anaerobic environment
In some cases, a normal product of fermentation may allow bacteria
to be more pathogenic. For example, Clostridium perfringens, which
causes gas gangrene, is an obligate anaerobe. When endospores
enter a deep wound with no oxygen, the endospores can germinate.
The vegetative Clostridia, which get their energy from fermentation,
can ferment tissue sugar to produce gases (carbon dioxide and
hydrogen) as end products. The gases accumulate in the enclosed
space and physically tear the tissue allowing the organism to spread.
This spreading ability is further aided by alpha, kappa, and mu
exotoxins mentioned in Unit 1.)
c. Temperature
Most pathogens have evolved to grow best at body temperature
(37C).
3. Some Relationships Between Factors Influencing Growth and the
Control of Bacteria
a. Temperature
1. Cold temperature, temperature below the minimum for growth,
generally has a static effect. It inhibits growth by slowing the rate of
metabolism and possibly causing ice crystals to form. Examples
include refrigeration, freezing, and extreme low cold.
2. High temperature, temperatures above the maximum for growth,
generally has a cidal effect. It kills organisms by denaturing enzymes
(moist heat) or causing desiccation and oxidation of proteins (dry
heat). Examples include autoclaving, boiling, dry heat, incineration,
and pasteurization.
b. Oxygen
1. The lack of oxygen may inhibit aerobic bacteria and molds (canned
foods for example), but it has no effect on obligate anaerobes and
facultative anaerobes.
2. The presence of oxygen may kill obligate anaerobes. For example,
a hyperbaric chamber employing saturated oxygen under pressure
may sometimes be of value in controlling gas gangrene caused by
anaerobic Clostridium species.
c. pH
Organic acids, such as calcium proprionate, potassium sorbate,
methylparaben, and sodium benzoate, are frequently used as food
preservatives. The low pH denatures microbial proteins.
d. Osmotic pressure
1. In conjunction with antibiotics or enzymes that alter peptidoglycan
(penicillins, cephalosporins, monobactems, glycopeptides,lysozyme,
etc.), a normal hypotonic environment which causes water to flow into
the bacterium may lead to bacterial lysis. Without these agents,
however, the peptidoglycan prevents osmotic lysis.
2. Making the bacterium's environment hypertonic by adding salts or
sugars may have a static effect on microorganisms by causing
plasmolysis (dehydration and shrinkage of the cytoplasmic
membrane due to an outflow of water). This is sometimes used in
food preservation.