Download QUIZ A - UniMAP Portal

QUIZ
ERT 317 BIOCHEMICAL ENGINEERING
1) Describe microbial growth and what are the results of growth to
microorganisms or cells?
[10 Marks]
 GROWTH - is the most essential response of microbes to their
physiochemical environment
 Result – replication and change in cell size
2) Demonstrate or illustrate the microbial growth phases by a graph or
diagram.
[10 Marks]
3) Explain each phases of microbial growth from the diagram.





[25 Marks]
Lag phase (adaptation)– just after inoculation, they take some time to
adjust to the new environment. Consequently, they start consuming the
nutrients in the medium and multiply
depending on composition of nutrient, new enzymes are synthesized,
some other enzymes are repressed & the internal machinery of cells is
adapted to the new environmental conditions
these changes reflect the intracellular mechanisms for regulation of
metabolic processes discussed in chapter 4
cell mass increase a little without an increase in cell number density
Pseudolag phase- when the inoculum is small and has a low fraction of
viable cells (poor condition of inoculum)
 Besides that low concentration of some nutrient and growth factors
and the age of the inoculum culture may also cause a long lag phase.
(the lag period increases with the age of inoculum.)
 Inoculum should be young and active. Inoculum size=5-10% by volume
 Diauxic growth – multiple lag phases is observed when the medium
contains more than 1 carbon sources. This caused by a shift in
metabolic pathways in the middle of a growth cycle.
 Log phase (logarithmic growth phase) – Cells have adjusted to their
new environment
 once the growth process starts, the cell multiply in an exponential order
(rapid). The growth is very fast. This is also known as exponential growth
phase. This phase is very important and all the kinetic growth
parameters are studied in this phase. Since the growth is exponential in
nature, when the cell concentration is plotted versus time on a semi-log
plot, the log phase results in straight line.
 This is a period of balanced growth – All component of cell grow at the
same rate. The average composition of a single cell remain
approximately constant during this phase.
Deceleration growth phase: growth decelerates due to either
depletion of one or more essential nutrients or the accumulation of
toxic by-products of growth. These changes occurred over a very short
period of time.
 The rapidly changing environment results in unbalanced growth
 During unbalanced growth, cell composition and size will change td
will not be equal.
 In this phase, the stresses induced by nutrient depletion or waste
accumulation cause a restructuring of the cell to increase the
prospects of cellular survival in a hostile environment.

Stationary phase – Once the cell numbers reach a maximum (point C),
they stop growing any more (net growth rate is zero). Hence, the
growth become stagnant and the growth continues to point D. It is
probably in this period, that they start converting the substrate into
metabolic products. More and more amount of substrate goes for
biochemical reaction to yield some useful products.
 Even though the net growth rate is zero during stationary phase, cells
are still metabolically active and produce secondary metabolites.
 Primary metabolites are growth related products
 Secondary metabolites are non-growth related.
 These phenomena may take place during stationary phase:
1. Total cell mass concentration may stay constant, but the number of
viable cells may decrease
2. Cell lysis may occur and viable cell mass may drop.
Cells may not be growing but may have active metabolism to produce
secondary metabolites.
•
•
•
•
•
Stationary phase
The cells catabolizes cellular reserves for new building blocks & for
energy-producing monomers – endogenous metabolism
The cell must always expend energy to maintain an energized
membrane and transport of nutrients and for essential metabolic
functions such as motility and repair of damage to cellular structures.
This energy maintenance is called maintenance energy.
The reason for termination of growth may be either exhaustion of an
essential nutrient or accumulation of toxic products.
If inhibitory product is produced and accumulates in the medium, the
growth rate will slow down, depending on the inhibitor production, and
at a certain level of inhibitor concentration, growth will stop.
 Death phase – the cells start decaying. After point D, probably cells
face shortage of substrate for their consumption. Hence, they start
decaying.
 The death phase (or decline phase) follows the stationary phase. Some
cell death may start during the stationary phase. Often, dead cell lyse,
and intercellular nutrients release into medium are used by the living
organism during stationary phase.
 At the end of the stationary phase (because of nutrient depletion or
toxic product accumulation, the death phase begins. The
reestablisment of the culture may be possible in the early death phase
if cells are transferred into a nutrient-rich medium.
4) List the three major categories of microbial products and give
examples.
[10 Marks]