2. Microbiology
Definition : study of microorganisms, or microbes, a diverse group of generally minute, simple
life forms. Eg. Bactria, algae, fungi.
Eukaryotes : Eukaryote, any cell or organism that possesses a clearly defined nucleus
Prokaryotes : Prokaryote is a single cell or organisms that does NOT have organized nuclei.
Microscopy : Act of using microscope to view tiny things that can not be seen by unaided eye
Culture : Act of cultivating microorganisms or the microorganisms that are cultivated.
6. • organized into 3 categories :
• Internal Structures: Cytoplasm, nucleoid, bacterial chromosome, plasmid,
ribosomes, and storage granules
• Cell envelope: cell membrane, peptidoglycan cell wall or an outer lipid
membrane (only found in Gram-negative cells)
• External structures (appendages & coverings): flagella, fimbriae, sex pilus
and glycocalyx
STRUCTUR OF BACTRIA
7. Growth of Bacteria
• Growth of Bacteria is the orderly increase of all the chemical constituents of the
bacteria.
• Multiplication is the consequence of growth.
• Death of bacteria is the irreversible loss of ability to reproduce. Bacterial growth follows
four phases.
• lag phase
• log phase
• stationary phase
• death phase
8.
9. Factor affecting bacterial growth
• Nutritional supplement
• Temperature
• Ph
• Oxygen Concentration
• Water Availability
• Pressure
• Radiation
• Sources of metabolic energy
10. Nutritional supplement
• Nutrients in growth media must contain all the elements
necessary for the synthesis of new organisms.
• Hydrogen donors and acceptors
• Carbon source
• Nitrogen source
• Minerals : sulphur and phosphorus
• Growth factors: amino acids, purines, pyrimidines; vitamins
• Trace elements: Mg, Fe, Mn.
11. Temperature
• Microorganisms are sensitive to temperature changes
• Usually unicellular
• Enzymes have temperature optima
• If temperature is too high, proteins denature, including enzymes, carriers
and structural components
Temperature ranges are enormous (-20 to 100oC)
13. PH
– Ph is the negative logarithm of the hydrogen ion concentration
– Acidophiles grow best between pH 0 and 5.5
– Neutrophiles grow best between pH 5.5 and 8.0
– Alkalophiles grow best between pH 8.5 and 11.5
– Extreme alkalophiles grow best at pH 10.0 or higher
– Sudden pH changes can inactivate enzymes and damage plasma
membrane
14. OXYGEN CONCENTRATION
– Obligate aerobes are completely dependent on atmospheric O2 for
growth
• Oxygen is used as the terminal electron acceptor for electron
transport in aerobic respiration
– Facultative anaerobes do not require O2 for growth, but do grow
better in its presence
– Aerotolerant anaerobes ignore O2 and grow equally well whether it
is present or not
– Obligate (strict) anaerobes do not tolerate O2 and die in itspresence.
15. WATER AVAILABILITY
• Water is solvent for biomolecules, and its availability is critical for cellular
growth
• The availability of water depends upon its presence in the atmosphere
(relative humidity) or its presence in solution or a substance (water activity,
(Aw))
• Aw of pure water (100%) is 1.0; affected by dissolved solutes such as salts
or sugars.
• Microorganisms live over a range of aW from 1.0 to 0.7. The aW of human
blood is 0.99; seawater = 0.98; maple syrup = 0.90; Great Salt Lake = 0.75.
Water activities in agricultural soils range between 0.9 and 1.0.
16. PRESSURE
Barotolerant organisms are adversely affected by increased pressure, but not as severely as are
nontolerant organisms
–Barophilic organisms require, or grow more rapidly in the presence of increased pressure
–Light : Optimum condition for growth is darkness.
17. RADIATIO
N
-Ultraviolet radiation damages cells by causing the formation of
thymine dimers in DNA.
– Ionizing radiation such as X rays or gamma rays are even more
harmful to microorganisms than ultraviolet radiation
• Low levels produce mutations and may indirectly result in
death
• High levels are directly lethal by direct
damage to cellular macromolecules or
through the production of oxygen free
radicals
18. (B) SOURCES OF METABOLIC ENERGY
• Mainly three mechanisms generate metabolic energy. These
are
• Fermentation
• Respiration and
• Photosynthesis.
An organism to grow, at least one of these mechanisms
must be used.
