This document discusses the bacterial growth curve, which consists of four phases: lag phase, log or exponential phase, stationary phase, and death phase. It provides details on each phase, including that the lag phase lasts 1-4 hours as bacteria adapt to their environment, the log phase is characterized by rapid, exponential cell division, and the stationary phase occurs when resources are depleted and growth levels off. Mathematical calculations for determining generation time from growth data are also presented, worked through using an example.

1. Reaacredited with B grade with a CGPA of 2.71 in the second cycle of NAAC
affiliated to manomanium sundaranar university, Tirunelveli.
Post graduate & Research Centre – Department of
Microbiology
(government aided)
I SEM CORE: MICROBIAL PHYSIOLOGY AND METABOLISM
(ZMBM13)
UNIT-5
BACTERIAL GROWTH CURVE
S . SARAL BEEVI SUBMITTED TO
REG.NO:20211232516123 GUIDE :DR. VISWANATHAN. PH.D.,
I. M. SC. MICROBIOLOGY ASSISTANT PROFESSOR AND HEAD
ASSIGNED ON : 05/12/2022 SPKC ALWARKURCHI
TAKEN ON : 12/01/2022

2.  INTRODUCTION
 GROWTH CURVE-FOUR PHASES
 LAG PHASE
 LOGPHASE
 LIMITATIONS OF LOG PHASE
 STATIONARY PHASE
 DEATH PHASE
 MATHEMETICAL CALCULATIONS OF GROWTH
CURVE OF BACTERIA
 CALCULATION OF GENERATION TIME
 EXAMPLE
 REFERENCES

3.  Bacterial growth is regulated by nutritional
environment.
 When suitable environment is there that time bacterium
is incubated, its growth leads to increase in number of
cells which allow definite course.

4. The growth curve has got four phases:
 Lag phase
 Log phase or exponential phase
 Stationary phase
 Decline phase

5. LAG PHASE(1-4 HOUR)
➢Bacteria adapt themselves to growth conditions. It is
the period where the individual bacteria are maturing
and not yet able to divide.
➢During the lag phase of the bacterial growth cycle,
synthesis of RNA, enzymes, and other molecules
occurs.
➢Length of this phase depend on type of bacterial
species, culture medium, and environmental factors.

7.  It is a period characterized by cell doubling. The number of new
bacteria appearing per unit time is proportional to the present
population.
 The rate of cell division is currently at its maximum with the
number of bacteria doubling as often as every 20 minutes.
 Exponential growth is balanced growth .i.e., all cellular
constituents are manufactured at constant rates relative to each
other.
 The population is most uniform in terms of chemical and
physiological properties during this phase; therefore log phase
cultures are usually used in biochemical and physiological
studies.

9. Limitations of log phase:
 Exhaustion of nutrition
 Accumulation of toxic metabolites and products
 Rise in cell density
 Change in PH.
(Log phase is the time when cells are most active
Metabolically and is preferred for industrial
purpose)

10.  The rate of growth levels stop during this
period.
 This is because:
❑The nutrients are becoming used up
❑The amount of waste produced by the bacteria
themselves is increasing.
❑The rate at which new cells are produced is
equal to the rate at which other cells are dying.

12.  During this phase more bacteria are dying than
are being produced. This is because:
• Very few nutrients are left
• Many bacteria are poisoned by the waste
produced by such large numbers.
• Finally, after certain time period all the cells
die and culture becomes sterile.

13. Generation time-Doubling time
 During the exponential phase each
microorganism is dividing at constant
intervals.
 Thus the population will double in number
during a specific length of time called the
generation time or doubling time.

14. G (generation time) = (time, in minutes or
hours)/n(number of generations)
G = t/n
t = time interval in hours or minutes
B= number of bacteria at the beginning of a time
interval
b = number of bacteria at the end of the time interval
n = number of generations (number of times the cell
population doubles during the time interval)

15. b = B x 2n (This equation is an expression of growth by binary
fission)
Solve for n:
Log b = log B + n log2 ; n Log2 = log b – log B
n = log b – log B
log2
( The value of log 2 is 0.301 & log b – log B = log b/B )
n = log b – log B ; n = 1 log (b/B)
0 .301 0.301
n = 3.3 log b/B
G = t/n
Solve for G
G = t/(3.3 log b/B)

17. b = 10⁷; B = 10⁴ ; t = 240 minutes
G = t/(3.3 log b/B)
G = 240 minutes
3.3 log 107/104
G = 240 minutes
3.3 log 10³
G = 240 minutes ; G = 240 minutes
3.3 x 3 (Log 10³ = 3) 9.9
G = 24 minutes
Therefore, generation or doubling time is 24 minutes

18. 1. Prescott’s Microbiology
2. Microbiology Principles and Explorations- Jacquelyn
G. Black.
3. www.microbenotes.com
4. www.biologydictionary.net
5. www.microbeonline.com

22.  Communication skill is developed.
 Confidence level is increased.
 Searching capability is increased.
 Gained subject knowledge better.
 Presentation skills are improved.
 Learn the time management.