PHCY219 – Microbiology Section 1 – Lecture 2 Judith Bateman
Lecture 2 – Microbial Growth
1.Describe microbial growth and process of binary fission
Microbial growth refers to the growth of the population (# in the colony) rather than the
size of the individual cell.
Need to know this diagram for the first objective of the
This top rod cell is called the parent cell
Duplication of bacterial chromosome can be seen in the
second part of the diagram
The bacteria make more cell wall and form the septum.
From the diagram we can also see that the DNA migrates.
The cell divides.
Now there are two separate cells (two daughter cells)!
Binary fission complete.
This diagram represents binary fission of coccyl (spherical)
bacteria. It demonstrates that this type of division can lead
to a great increase in population number. Refer to table.
1 | P a g e PHCY219 – Microbiology Section 1 – Lecture 2 Judith Bateman
Generation mean time = how long it take the division process to finish (i.e. – time it takes
for a cell to divide)
- Generation mean time varies for different species. For example, E. coli takes 20
minutes whereas M. tuberculosis takes a whole day!
We can plot the growth on a graph, however because
the growth is exponential, it can be difficult to graph
with a linear scale. So we use logarithmic scale instead.
The division plane is important
because it dictates the cell
If plane of division is in the
same plane it makes a chain.
If the plane of division is in
many planes that the result will
be a cluster of bacteria
2 | P a g e PHCY219 – Microbiology Section 1 – Lecture 2 Judith Bateman
- Physical Factors
o Gaseous Atmosphere
Definitions (memorise these!)
Aerobes These organisms need oxygen
In the electron transport chain, the terminal
electron acceptor is oxygen
Anaerobes They like to live in places where there is an
absence of oxygen
Their final electron acceptor in the electron
transport chain is NOT oxygen. It is exogenous e.g.
– nitrate & sulphate
NOTE: Fermentation absence of electron
Facultative Anaerobes They can grow with or without (but they don’t
grow as well without oxygen). Indicates that they
might have two different ways of metabolism to
Microaerophiles These organisms like to live in areas where there is
oxygen but not too much
Capnophiles An abundance of carbon dioxide is needed for
capnophiles to grow.
This diagram illustrates that different
microbes have different
requirements for oxygen. We can tell
by the different distributions along
the column. If there is a dense
distribution near the top then it’s
likely that they need oxygen.
Conversely if the organisms are
packed at the bottom, then operate
in the absence of oxygen. This is why
some blood cultur