This was an assignment of preparing “A lecture note on Microbial Growth and Nutrition, and Clones, Enzymes and Informative Hybridizations” for the course "General Microbiology" Hope you will find it useful.

1. A lecture note on Microbial Growth and
Nutrition, and Clones, Enzymes and
Informative Hybridizations.
Prepared by Md. Akram Hossain
B. Sc. In Food and Process Engineering, HSTU
M. Sc in Agro – Processing, BSMRAU

2. Microbial Growth

3. Microbial growth
• In everyday language, growth refers to an increase
in size.
• But microbial growth refers to the growth of a
population (or an increase in the number of cells).
• In favorable conditions, microbial growth occurs,
sexually and asexually (usually occurs by binary
fission or sometimes by budding).

4. Microbial growth
Binary fission
• In binary
fission, a cell
duplicates its
components
and divides
into two cells.

5. Microbial growth
Budding
• Cell division in yeast and a few
bacteria occurs through
budding. In that process, a
small, new cell develops from
the surface of an existing cell
and subsequently separates
from the parent cell.

6. Microbial growth
Phases of growth
Microorganisms display four major phases of growth.
These phases form the microbial growth curve :
• (1) the lag phase,
• (2) the log
(logarithmic) phase,
• (3) the stationary
phase, and
• (4) the decline phase

7. Microbial growth > Phases of growth
The lag Phase
• In the lag phase, the organisms are metabolically
active—growing and synthesizing various
substances but not increasing in number.

8. Microbial growth > Phases of growth
The log Phase
• In the log phase, organisms divide at an exponential,
or logarithmic, rate and with a constant generation
time.
• generation time. (also called division time) the time required for a population of cells to
double in number. the time required for a generation of individuals to be born, reach sexual
maturity and reproduce.

9. Microbial growth > Phases of growth
The stationary phase
• In the stationary phase, the number of new cells
produced equals the number of cells dying. The
medium contains limited amounts of nutrients and
may contain toxic quantities of waste materials.

10. Microbial growth > Phases of growth
The decline phase
• In the decline phase, or death phase, many cells
lose their ability to divide and eventually die. A
logarithmic decrease in the number of cells results.

11. Microbial growth
Measuring bacterial growth
• Growth can be measured by
serial dilution, in which
successive 1:10 dilutions of a
liquid culture of bacteria are
made and transferred onto an
agar plate; the colonies that
arise are counted. Each colony
represents one live cell from
the original sample.

12. Microbial growth
Measuring bacterial growth
• Growth also can be measured by direct microscopic
counts, the most probable number (MPN) technique,
filtration, observing or measuring turbidity,
measuring products of metabolism, and obtaining the
dry weight of cells.

13. Microbial Nutrition

14. Microbial Nutrition
• The growth of microorganisms is affected by
nutritional factors, as well as by physical factors.
• Nutrients needed by microorganisms include
carbon, nitrogen, sulfur, phosphorus, certain trace
elements, and vitamins.

15. Microbial Nutrition
• All organisms, including microbes, can be classified
metabolically according to their nutritional pattern-
their source of energy and their source of carbon.
• First considering the energy source, we can
generally classify organisms as phototrophs or
chemotrophs.
• For their principal carbon source, they can be
autotrophs (self-feeders) and heterotrophs (feeders
on others).

16. Microbial Nutrition

17. Microbial Nutrition
• Chemoautotrophs (Chemolithotrophs) - use
inorganic substrates as sources of energy and C02
as the main source of carbon.
• Chemoheterotrophs (Chemorganotrophs) - utilize
organic substrates for both needs.
• Photoautotrophs (Photolithotrophs) - use light as
energy source and C02 as carbon source.
• Photoheterotrophs (photoorganotrophs) - use light
as energy source and organic carbon.

18. Microbial nutrition
Nutrient Transport Processes
Having found a source of a given nutrient, a
microorganism must: have some means of taking it
up from the environment and possess the
appropriate enzyme systems to utilize it.
A substance can be transported across the cell
membrane in one of three ways, known as
• simple diffusion,
• facilitated diffusion and
• active transport.

19. Microbial nutrition > Nutrient Transport Processes
Simple diffusion
• Movement of substances directly across a
phospholipid bilayer, with no need for a transport
protein
• Movement from high to low concentration
• No energy expenditure (e.g. ATP) from cell
• Small uncharged molecules may be transported via
this process, e.g. H2O, O2, CO2

20. Microbial nutrition > Nutrient Transport Processes
Facilitated Diffusion
• Movement of substances across a membrane with
the assistance of a transport protein
• Movement from high to low concentration
• No energy expenditure (e.g. ATP) from cell
• Two mechanisms: Channel & Carrier Proteins

21. Microbial nutrition > Nutrient Transport Processes
Active Transport
• Movement of substances across a membrane with
the assistance of a transport protein
• Movement from low to high concentration
• Energy expenditure (e.g. ATP or ion gradients) from
cell
• Active transport pumps are usually carrier proteins

22. Microbial nutrition
Growth media
• In nature, microorganisms grow on natural media,
or the nutrients available in water, soil, and living or
dead organic material.
• In the laboratory, microorganisms are grown in
synthetic media:
• A defined medium is one whose precise chemical
composition is known.
• An undefined or complex medium is one whose precise
chemical composition is not known.

23. Microbial nutrition
Growth media
• Diagnostic media are
• A selective medium is one that favors the growth of a
particular organism or group of organisms, often by
suppressing the growth of others.
• A differential medium allows colonies of a particular
organism to be differentiated from others growing in the
same culture.
• An enrichment culture uses a selective medium to
encourage the growth of an organism present in low
numbers.

24. Clones and hybridization

25. Clones
• Clones are organisms that are exact genetic copies.
Every single bit of their DNA is identical.
• Clones can happen naturally—identical twins are
just one of many examples. Or they can be made in
the lab.

26. Clones
• When scientists clone a gene, they isolate and
make exact copies of just one of an organism's
genes. Cloning a gene usually involves copying the
DNA sequence of that gene into a smaller, more
easily manipulated piece of DNA, such as a plasmid.
This process makes it easier to study the function
of the individual gene in the laboratory.

28. DNA–DNA hybridization
• DNA–DNA hybridization generally refers to a
molecular biology technique that “measures the
degree of genetic similarity between pools of DNA
sequences.”
• It is usually used to determine the genetic distance
between two organisms. This has been used
extensively in phylogeny and taxonomy.

29. DNA–DNA hybridization

30. Thank you