6. Microbial Growth
for microbial growth:
subgroups physical and chemical.
include: Temperature, pH and osmotic pressure.
include: Sources of carbon, nitrogen, oxygen, hydrogen, sulfur,
phosphorous and trace elements.
most microorganisms grow at temperatures favored by humans.
cold loving microbes. Many wont grow at room temp.
Microbes grow in a
small range of temps. their maximum and minimum temps. Often vary by only
species grows at a particular minimum, optimum and maximum
growth temperature (Fig 6.1).
Some archea grow at extremes like hypertermophiles.
bacteria grow best near neutral 6.5ΰ7.5.
This is why pickles
and sauerkraut are protected because most bacteria can not survive in that
are they made?
do you combat this problem?
can grow in acidic environs including some at a pH of 1.
Fungi tend to live
in slightly acidic environs pH 5-6.
Ex: Saccharomyces cerevisiae.
Pressure: microbes need a certain osmotic pressure to maintain integrity
and get nutrients.
If a microbe is in a
hypertonic solution (what is this?) water will leave the cell and the cell
is a shrinkage of the cell plasma membrane (Fig. 6.4).
halophiles on the other
hand require high salt concentrations to survive.
Facultative halophiles are able to grow in high-salt conditions up to 2%
some even up to 15%.
Carbon is the
structural backbone of living matter and necessary for all organic
get most of their carbon from the source of their energy; proteins,
carbohydrates and lipids.
Chemoautotrophs get their carbon from CO2.
Nitrogen, sulfur and
synthesis needs nitrogen and phosphorous.
synthesis needs nitrogen and some sulfur.
makes up about 14% of the dry weight of the cell.
bacteria use Nitrogen fixation to get usable nitrogen this can be
done as a free living organism or as in symbiosis.
Roots of legumes like soybeans, beans and peas.
elements are very small amounts of certain elements that are needed.
Ex: Iron, copper,
a necessity of life or a poison (Table 6.1)?
Oxygen is poisonous
at high concentrations and is often combined with hydrogen to form water
neutralizing the poison.
Some microbes do use
since water doesnt dissolve well in water or in many environments.
many organisms are facultative anaerobes.
grow in the absence or presence of oxygen.
and most importantly yeast.
cannot use molecular oxygen and most are harmed by it.
oxygen includes H2O2, Superoxide (O2-)
and hydroxyl radical (OH.).
obligate anaerobes dont have the enzymes to deal with these reactive
oxygen species (ROS).
anaerobes cannot use oxygen but tolerate it well.
only grow in low concentrations of oxygen.
growth factors directly obtained from the environment.
Ex = vitamins
is nutrient material prepared for microorganism growth.
introduced into a culture are an inoculum.
that grow in or on a culture are referred to as a culture.
Culture media must
is a complex polysaccharide made from a marine algae.
Used in jellies and
Important properties: microbes cannot degrade it, liquefies at 100oC and solidifies at 40oC.
is one in which the exact chemical composition is known.
Used for laboratory
experimental work or autotrophic bacteria.
is made up of nutrients from extracts of yeasts, meat, plants or digests
Nutrient broth and
growth Media and Methods.
Must use reducing
media that contain chemicals like sodium thioglycolate that combine
with oxygen to deplete it.
If you need to grow an anaerobe on a plate a anaerobic jar may be used (Fig 6.5).
cannot be cultured easily on laboratory media.
Mycobacterium leprae cultured in armadillos.
may have special incubators for anaerobes and capnophiles (microbes
that grow better with increased CO2) (Fig 6.7).
and differential media are used to detect the presence of specific
media are used to suppress the growth of unwanted bacteria and encourage
the growth of desired microbes.
Example: Sabourads dextrose agar which has a pH of 5.6 is used to isolate fungi because of pH.
media make it easier to distinguish between colonies of the desired
organism from other colonies.
Streptococcus pyogenes the bacteria causes lysis of the
blood cells in blood agar and makes a ring around the cells.
is usually a liquid media and provides nutrients and environmental
conditions that favor the growth of a particular microbe.
To increase the
number of a microbes to prevent missing a microbe that may be in small
Often used on soil
or fecal samples.
Example: soil sample looking for bacteria that grow on phenol. Culture ΰ Move ΰ Grow ΰMove ΰ Grow Growth is the enrichment stage.
starting materials contain many organisms.
If these materials
are plated out they will form colonies that are exact copies of the
A visible colony arises from a single spore or vegetative cell or from a group of the same organism attached to one another in clumps or chains.
work requires pure colonies.
One way to recover
pure single colonies is the streak plate method (Fig 6.10).
work well when the numbers of that cell type are low.
selective enrichment first if cell number is low.
is a process by which a culture is placed in suspension medium and frozen
at temperatures between 50oC and 95oC.
Most commonly done
at ~-80oC in ultra-low freezers.
Suspension media is
often Nutrient broth and 15% glycerol.
Lyophilization (freeze-drying) the organism is quik frozen as above and dried under a
culture growth: Analyzing the growth of bacterial cultures is an essential
part of bacteriology.
Bacterial growth refers not to the increase in size of cells but the
increase of numbers of cells.
A few bacteria reproduce by budding.
the time required for a cell to divide (Fig 6.12).
When the number of
cells in each generation is expressed as the power of 2 the exponent tells
the number of doublings (generations) that have occurred.
time can be as low as 20 minutes (E. coli) and as high as 24 hours
20 generations a single cell of E. coli would be over 1,000,000.
generations = 10 hours = 1,000,000,000
to graph such high numbers that is why logarithmic scales are used, bacterial
growth curve (Fig 6.13).
representations are much easier to graph and is necessary for proper
understanding of microbial populations.
Microbial Growth: When a few bacteria are inoculated into a liquid and the
population counted at intervals it is possible to plot a bacterial
Four Basic Phases of Growth: Lag phase, Log Phase Stationary phase and death phase (Fig 6.14).
of intense metabolic activity including DNA and enzyme sythesis.
The log phase or
exponential growth phase- cellular reproduction is at its most active.
equals a constant minimum rate that is why you see a straight line.
are at their most sensitive here many antimicrobial agents work best
during this phase by interfering with growth (Penicillin).
phase is when cell death equals new cells and the metabolic
activity of cells decline.
be combated by replacing spent medium with fresh medium.
Death phase or logarithmic decline occurs when deaths outnumber new cells.
Measurement of Growth.
populations are usually measured by cell number per milliliter or
by population mass.
Because of the
incredible numbers of cells in a bacterial population they are usually measured
indirectly or directly in small sample sizes.
Dilutions are done
to count cells more easily.
Assumes that each living cell produces a single colony.
however form from chains or clumps and are expressed as colony forming
Serial dilutions down to approximately < or = 250 cells are best (Fig. 6.15).
Pour plates and
spread plates (Fig 6.16).
have colonies suspended in the medium
be hard to visualize.
have the cells spread across the surface of a solidified medium.
spread with a bent glass rod.
bacteria can be passed through a filter to trap them and then they can be
transferred to a petri plate containing appropriate medium.
to recover bacteria out of water.
Statistical estimating technique based on the fact that the more bacteria
the more dilutions needed to get no bacteria.
most often for bacteria that do not grow on solid media.
Microscopic count uses a specifically designed Petroff-Hausser cell counter slide to microscopically count the cells in a known volume (Fig 6.19).
uses a spectrophotometer to estimate the number of cells (Fig 6.20).
a spectrophotometer light is transmitted through a dilution of the
culture (usually a 1:10 dilution)
microbe numbers increase light passing through the culture decreases.
output is often absorbance or optical density.
is a logarithmic expression of the amount of light that gets through the
number of cells per absorbance unit is a known constant for most
turbidity use in cell counting.
Yeast 1.0 A600 unit = 107 cells (10,000,000).
A600= absorbance at a wavelength of 600 nm.
So if you are
reading a 1:10 dilution of your yeast culture and the absorbance from the
spectrophotometer reads as 0.1 you have a culture that has an A600
of 1.0 and has 10,000,000 cells per milliliter.
How many cells if the reading was 0.2?
activity can be used to
estimate cell number, the amount of some product produced in normal
organism activity can be used to estimate cell number.
CO2 or acid is directly proportional to cell count.
can be used especially for molds and other filamentous microorganisms.
is dried and then weighed.