Physical Requirements:
Temperature- Most microorganisms grow well at the temperatures favored by humans but able to grow at extremes.
Classified under three groups- psychrophiles (cold-loving microbes), mesophiles (moderate temperature
loving microbes), and thermophiles (heat-loving microbes). Most bacteria grow within a range of their
minimum and maximum temperate which is only about 30 degrees apart from one another. They grow
best however in the middle of the range. There are three catagories of temperature. Minimum growth
(lowest a species can grow at), optimum growth (where the species grows best at), and maximum
growth ( highest a species can grow at. To help see that the optimum growth temperature is usually at
the top, often a graph of growth response over temperature range is used. Above the top of that range,
the rate usually drops of rapidly because the necessary enzymatic systems in the cell are inactivated due
to the high temperatures. Ranges and growth temperatures are not always rigid. One example is
Psychrophiles who originally were thought to grow only at zero degrees but in reality can grow at zero
but also have an optimum temperature of 15 degrees. Psychrotrophs are organisms that are usually
found in low temperature food spoilage due to their ability to grow well at refrigerator temperatures.
These organisma are much more common than the psychrophiles. Refrigeration is the most common
way to preserve food supplies in homes because of the idea that microbial growth decreases the lower
the temperature. They can even survive subzero freezing, however, they do slowly decline in
temperature with that.
pH- most bacteria grow best in a narrow pH range near neutrality and few grow at extremes of either highs
or lows of pH. Acidophiles however are tolerant of acidity. Bacteria growth in laboratories often produce
acids that interfere with their own growth, so chemical buffers are needed to help balance in the growth
medium.
Osmotic Press.- microorganisms get most of their nutrients in solution surrounding them, and because they are made
up of 80-90% water, they require water for growth. Plasmolysis is caused by a osmotic loss of water, or a
shrinkage of the cytoplasm. Addition of salts in a solution increase the osmotic pressure. Organisms
that are adapted to high salt concentrations and actually need them for growth are extreme halophiles
or obligate halophiles. Faculative halophiles do require this.
Some Chemical Requirements:
Carbon- most important requirements for growth besides water becaue it is the structural back boneof living
matter.
Trace Elements- the small amount of other materials a microbe requires that are essential for functions of certain
enzymes. Sometimes these are added in a laboratory, other times they are added naturally.
Temperature- Most microorganisms grow well at the temperatures favored by humans but able to grow at extremes.
Classified under three groups- psychrophiles (cold-loving microbes), mesophiles (moderate temperature
loving microbes), and thermophiles (heat-loving microbes). Most bacteria grow within a range of their
minimum and maximum temperate which is only about 30 degrees apart from one another. They grow
best however in the middle of the range. There are three catagories of temperature. Minimum growth
(lowest a species can grow at), optimum growth (where the species grows best at), and maximum
growth ( highest a species can grow at. To help see that the optimum growth temperature is usually at
the top, often a graph of growth response over temperature range is used. Above the top of that range,
the rate usually drops of rapidly because the necessary enzymatic systems in the cell are inactivated due
to the high temperatures. Ranges and growth temperatures are not always rigid. One example is
Psychrophiles who originally were thought to grow only at zero degrees but in reality can grow at zero
but also have an optimum temperature of 15 degrees. Psychrotrophs are organisms that are usually
found in low temperature food spoilage due to their ability to grow well at refrigerator temperatures.
These organisma are much more common than the psychrophiles. Refrigeration is the most common
way to preserve food supplies in homes because of the idea that microbial growth decreases the lower
the temperature. They can even survive subzero freezing, however, they do slowly decline in
temperature with that.
pH- most bacteria grow best in a narrow pH range near neutrality and few grow at extremes of either highs
or lows of pH. Acidophiles however are tolerant of acidity. Bacteria growth in laboratories often produce
acids that interfere with their own growth, so chemical buffers are needed to help balance in the growth
medium.
Osmotic Press.- microorganisms get most of their nutrients in solution surrounding them, and because they are made
up of 80-90% water, they require water for growth. Plasmolysis is caused by a osmotic loss of water, or a
shrinkage of the cytoplasm. Addition of salts in a solution increase the osmotic pressure. Organisms
that are adapted to high salt concentrations and actually need them for growth are extreme halophiles
or obligate halophiles. Faculative halophiles do require this.
Some Chemical Requirements:
Carbon- most important requirements for growth besides water becaue it is the structural back boneof living
matter.
Trace Elements- the small amount of other materials a microbe requires that are essential for functions of certain
enzymes. Sometimes these are added in a laboratory, other times they are added naturally.