of the most common ways bacteria are grown in a lab is called batch
batch culture, bacteria are added to a fixed amount of liquid growth
a solution that contains nutrients for bacterial growth and allowed to grow
under defined environmental conditions.
growth in batch culture follows a predictable pattern of four phases:
Immediately after they are added to a new media bacteria must adjust their
metabolism to the new environment before they begin growing and dividing. The
number of bacteria in the culture does not change during this phase.
Bacteria actively grow and divide, and the number of bacteria in the culture
an essential nutrient in the media is depleted, growth slows substantially,
such that growth rate in the culture becomes equal to death rate. The number of
bacteria in the culture is unchanged.
culture conditions can no longer sustain any growth, bacteria die off
Phases 2-4 will happen in every batch culture, given enough time. However, it
is possible for no lag phase to be observed if little or no adjustment of
metabolism is needed for the bacteria to begin reproducing in their new
following experiments was conducted to investigate the variables that affect
bacterial growth in batch culture.
A batch culture of E. coli, a common bacterial species used
for lab studies, was grown in a nutrient rich media called LB.
When this culture reached log phase, 0.5 ml samples of the liquid media was
removed and used to inoculate each of two 1L flasks. Each of these flasks
contained a different type of liquid growth media. The new cultures were then
allowed to grow at 37°C.
of the cultures was monitored by taking periodic measurements of the optical
or OD600, of
the growth media. Optical density is a measurement of how easily light is able
to pass through the media, and it is directly related to the
concentration of living bacteria in the media. The resulting measurements are
graphed in Figure 1.
Eight 1L flasks of minimal growth media were inoculated with bacteria: four
with E.coli, and
four with P.
The flasks were then incubated at 37°C under one of two conditions--either
with, or without oxygen--and OD600
measurements were taken every hour to monitor growth.
measurements stopped rising, the bacteria was separated from the media and
weighed. These measurements were used to calculate growth
the percentage of carbon source(s) in the growth media that was converted to
biological material. Growth yield can be used to determine how efficiently the
bacteria are able to use energy during a given set of growth conditions. The
results of these calculations are shown in Table 1.