General requirements
for the bacterial growth:
Factors Influencing
Bacterial Growth
1. Physical requirements
a. Temperature
Bacteria have a minimum,
optimum, and maximum temperature for growth and can be divided into 3 groups
based on their optimum growth
temperature:
1. Psychrophiles are cold-loving bacteria. Their optimum growth temperature is below
20 degree Celsius and also as low as 2-6 degree celsius. They are usually found
in the Arctic and Antarctic regions and in streams fed by glaciers.eg. Yersinia
enterocolitica,Listeria monocytogenes,etc.
2. Mesophiles are bacteria that grow best at moderate temperatures. Their
optimum growth temperature is between 25C and 45C. Most bacteria are mesophilic
and include common soil bacteria and bacteria that live in and on the body.eg.
Salmonella.Shigella,Staphyllococcus,Vibrio,etc.
3. Thermophiles are heat-loving bacteria. Their optimum growth
temperature is between 60 C and 70C and are comonly found in hot springs and in
compost heaps.Bacillus stearothermophilus.
4. Hyperthermophiles are bacteria that grow at very high
temperatures. Their optimum growth temperature is between 70C and 110C. They
are usually members of the Archae and are found growing near hydrothermal vents
at great depths in the ocean.
b. Oxygen requirements
Microorganisms show a
great deal of variation in their requirements for gaseous oxygen. Most can be
placed in one of the following groups:
1. Obligate aerobes are organisms that grow only in the presence of oxygen. They obtain their energy through
aerobic respiration .
2. Microaerophiles are organisms that require a low concentration
of oxygen (2% to 10%) for growth, but higher concentrations are inhibitory.
They obtain their energy through aerobic respiration
3. Obligate anaerobes are organisms that grow only in the absense of oxygen and, in fact, are often inhibited or
killed by its presense. They obtain their energy through anaerobic respiration or fermentation.
4. Aerotolerant anaerobes , like obligate anaerobes, cannot use oxygen to
transform energy but can grow in its presence. They obtain energy only by
fermentation and are known as
obligate fermenters.
5. Facultative anaerobes are organisms that grow with or without oxygen,
but generally better with oxygen. They obtain their energy through aerobic
respiration if oxygen is present,
but use fermentation or anaerobic respiration if it is absent. Most bacteria are facultative
anaerobes.
c. pH
Microorganisms can be
placed in one of the following groups based on their optimum pH requirements:
1. Neutrophiles grow best at a pH range of 5 to 8.
2. Acidophiles grow best at a pH below 5.5.eg. Lactobacillus
acidophilus in adult vagina.
d. Moisture
2/3 part of bacterial cell contains
water.so, water is very essential for the growth of bacteria.
2. Nutritional requirements
In addition to a proper
physical environment, microorgaisms also depend on an available source of
chemical nutrients.Microorganisms are often grouped according to their energy
source and their source of carbon.
a. Energy source
1. Phototrophs use radiant energy (light) as their primary energy source.
2. Chemotrophs use the oxidation and reduction of chemical compounds as their primary energy
source.
b. Carbon source
Carbon is the structural
backbone of the organic compounds that make up a living cell. Based on their
source of carbon bacteria can be classified as autotrophs or heterotrophs.
1. Autotrophs : require only carbon dioxide as a carbon source. An autotroph can
synthesize organic molecules from inorganic nutrients.
2. Heterotrophs : require organic forms of carbon. A Heterotroph cannot synthesize
organic molecules from inorganic nutrients.
Combining their
nutritional patterns, all organisms in nature can be placed into one of four
separate groups: photoautotrophs, photoheterotrophs, chemoautotrophs, and
chemoheterotrophs.
1. Photoautotrophs use light as an energy source and carbon dioxide as their main carbon source. They include
photosynthetic bacteria (green sulfur bacteria, purple sulfur bacteria, and
cyanobacteria), algae, and green plants. Photoautotrophs transform carbon
dioxide and water into carbohydrates and oxygen gas through photosynthesis .
Cyanobacteria, as well
as algae and green plants, use hydrogen atoms from water to reduce carbon
dioxide to form carbohydrates, and during this process oxygen gas is given off
(an oxygenic process). Other photosynthetic bacteria (the green sulfur bacteria
and purple sulfur bacteria) carry out an anoxygenic process, using sulfur,
sulfur compounds or hydrogen gas to reduce carbon dioxide and form organic
compounds.
2. Photoheterotrophs use light as an energy source but
cannot convert carbon dioxide into energy. Instead they use organic compounds as a carbon source. They include the green
nonsulfur bacteria and the purple nonsulfur bacteria.
3. Chemolithoautotrophs use inorganic compounds such as hydrogen sulfide, sulfur, ammonia, nitrites, hydrogen gas,
or iron as an energy source and carbon dioxide as their main carbon source.
4. Chemooganoheterotrophs use organic compounds as both an energy source and a carbon source. Saprophytes live on dead organic matter while parasites get their nutrients from
a living host. Most bacteria, and all protozoans, fungi, and animals are
chemoorganoheterotrophs.
c. 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.
d. Minerals
1. 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.
2. phosphorus
Phosphorus is needed to
synthesize phospholipids DNA, RNA, and ATP . Phosphate ions are the primary source of
phosphorus.
3. potassium, magnesium, and calcium
These are required for
certain enzymes to function as well as additional functions.
4. iron
Iron is a part of
certain enzymes.
5. 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.
f. 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 .
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