Bacterial physiology & bacterial growth

1. Microbial Growth
Dr. Md. Abdullah Yusuf
Assistant Professor, Dept. of Microbiology
National Institute of Neurosciences & Hospital
Dhaka, Bangladesh
Email: ayusuf75@yahoo.com

2. Learning Objective
Meaning of growth
Generation Time
Different growth Requirements
Growth curve with its clinical Significance

3. Microbial growth
Definition
– Means orderly increase in all the components of a cell
– Cell number is not increased
Indicated by increase in microbial population due
to binary fission
Number of progeny increases as per rule of
geometric progression e.g. 1 to 2, 2 to 4, 4 to 8, 8
to 16 etc.

4. Generation or Doubling Time
Time require to divide one bacterium into 2 is
called “generation time or doublung time”
Generally in the range of minutes for ordinary
bacteria and in the range of hours for slow
growing bacteria
Fastest Generation: Escherichia coli, Vibrio
cholerae
Longest Generation time: Mycobacterium leprae

5. Basic Nutritional Requirements
A SOURCE OF ENERGY. This may be
light (the sun or lamps) or
inorganic substances like sulfur, carbon
monoxide or ammonia, or
preformed organic matter like sugar,
protein, fats etc.

6. Basic Nutritional Requirements
A SOURCE OF NITROGEN.
• nitrogen gas
• ammonia
• nitrate/nitrite, or
• nitrogenous organic compound like
protein or nucleic acid

7. Bacterial nutrition
A SOURCE OF WATER.
Requires water in order to grow and reproduce
Some resting stages of cells, like bacterial spores,
can exist for long periods without free water, but
they do not grow or metabolize

8. Bacterial nutrition
A SOURCE OF MINERALS LIKE
IRON, ZINC, COBALT ETC. These are
called TRACE metals that are required by
some enzymes to function.

9. Bacterial nutrition
A SOURCE OF CARBON. This can be
carbon dioxide or monoxide,
Methane or
complex organic material

10. Bacterial nutrition
A SOURCE OF OXYGEN.
All cells use oxygen in a bound form
many require gaseous oxygen (air)
but oxygen is lethal to many microbes.

11. Bacterial nutrition
A Source Of Phosphorous, Sulfur, Magnesium,
Potassium & Sodium.
A Source Of Calcium.
– Most cells require calcium in significant
quantities,
– but some seem to only need it in trace amounts.

12. Bacterial nutrition
Many bacteria can synthesize every complex
molecule they need from the BASIC
MINERALS, but others, said to be
FASTIDIOUS, require PREFORMED organic
molecules like vitamins, amino acids, nucleic
acids, carbohydrates.

13. Other requirements for growth
Environmental (Physical) requirements
– 1. Temperature and moisture
»psychrophiles : Cold loving. 0 - 15o
C.
»mesophiles : Moderate temperature loving.
10 - 45o
C
»thermophiles : Heat loving. 46 - 64o
C.
»extreme thermophiles : 65 - 110o
C.
Have a minimum, optimum, and maximum
temperature of growth

14. The requirements for growth, cont.
Physical requirements
Osmotic Pressure
– Most cells live in isotonic solutions
– Hypertonic solutions dehydrate cells (Used for
food preservation)
»Halophile: Salt loving.
»Extreme or obligate halophiles :require high
salt (archaea).
»Facultative halophiles: can grow in high salt

15. The requirements for growth, cont.
Nutritional (Chemical ) Requirements
– 1. Carbon
»autotroph -Gets carbon from CO2.
»Heterotroph- Gets carbon from organic
source.
– 2. Nitrogen, sulfur, & phosphorous
»Nitrogen for proteins, DNA, RNA, ATP
»Sulfur for some amino acids & vitamins
»Phosphorous for nucleic acids, ATP,
phospholipids

16. The requirements for growth, cont.
Chemical requirements
Trace elements: potassium, magnesium, calcium,
iron, copper, molybdenum, and zinc.
– needed as cofactors for enzymes.
Oxygen
– Both useful and harmful
»Useful in respiration
»Harmful because is a strong oxidizing agent

17. The requirements for growth, cont.
Chemical requirements
– pH
»Optimum for most bacteria : pH 6 to pH 8
»Optimum for yeast: about pH 5
»Acidophiles (Lactobacillus) : grow at very
low pH.
»Alkalophiles (Vibrio cholerae) : grow at
high pH

18. The requirements for growth, cont.
Chemical requirements
Oxygen. Classification of organisms
– obligate aerobe Requires oxygen.
– facultative anaerobe Grows with or without
oxygen.
– obligate anaerobe Grows only in absence of
oxygen.
– microaerophile Grows in low oxygen
concentration and high CO2 tension
– aerotolerant anaerobe Grows in presence of
oxygen, but does not use it

19. The requirements for growth, cont.
Why is oxygen harmful?
– It is a strong oxidizing agent. It pulls electrons
off other molecules.
What is formed in presence of oxygen?
– Singlet oxygen
– Superoxide free radical: O2
-
– Hydrogen peroxide: H202
– Hydroxyl radical: OH-

20. The requirements for growth, cont.
Toxic compounds in turn pull electrons off other
molecules, e.g., lipids, proteins, and nucleic acids.
Result:
– Cell is harmed if it cannot get rid of toxic forms of
oxygen.
To get rid of toxic oxygen compounds, cells need:
– Superoxide dismutase (SOD)
»02
-.
+ 02
-.
+ 2H+
= H202 + 02
– Catalase
»2H202 2H20 + 02

21. I. The requirements for growth, cont.
Chemical requirements,
Organic growth factors may be needed
»Vitamins
»Amino acids
»Purines
»Pyrimidines

22. II. Population growth

23. Population growth, cont.
Steps of binary fission:
– 1. Cell elongates, and DNA replicates.
– 2. Cell wall and plasma membrane increase in
size and form septum.
– 3. Cross wall forms around DNA.
– 4. Cells separate.

24. II. Population Growth, cont.
Generation time varies
with:
– Organism
– Available nutrients
– Temperature
– pH, etc.
Can be short (10 min)
or long (hours)

26. II. Population growth, cont.
Case:
– 1 cell
– Generation time 30 min
– In 10 hrs have 1,048,576 cells
– 10 hrs = 20 generations
Get large numbers of cells quickly
Plot arithmetically or logarithmically

27. Growth curve
When a fresh medium is inoculated with a
given number of cells, and the population
growth is monitored over a period of time,
plotting the data will yield a typical
bacterial growth curve

29. Growth curve
Phases of growth:
– 1. Lag phase
»Cells are adjusting to environment.
»Cells are synthesizing needed
macromolecules
»No Multiplication
– 2. Log phase or exponential phase
»Cells are undergoing binary fission
»Cell wall antibiotics acts well

30. Growth curve
3.Stationary phase
– Growth rate slows down.
– Some cells die.
– Due to depletion of nutrients and/or
accumulation of waste
4. Death phase
– Cells die
– Spore formed

31. Log Phase Continue
Chemostate
Turbidostate
Thermostate

32. Thank You