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Lecture notes of 7 pages for the course MCB 201 at FNUniv (Understanding)
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COURSE SYNOPSISMCB 201: GENERAL MICROBIOLOGY I (3 UNITS)
LECTURERS: Prof (Mrs) M.O. Bankole*, Dr S.A. Balogun, Dr (Mrs) O.R. Afolabi
1. Biology of microorganisms: Nutrition, metabolism, growth and reproduction in
microorganisms
Nutritional Requirements
All forms of life, from microorganisms to human beings, share certain nutritional
requirements, in terms of the chemicals necessary for their growth and normal
functioning.
a. Source of Energy: microorganisms can be classified as
- Phototrophs: utilising radiant energy (sunlight) as sole source of energy
- Chemotrophs: depend on oxidation of chemical compounds for their energy.
b. Source of Carbon
- Autotrophs: Carbondioxide is their sole carbon source
- Heterotrophs: organic form of carbon as the sole source of carbon
c. Other nutrients: Water, Vitamins
d. Other elements: Nitrogen, Sulphur, Phosphorus, Sodium, Potassium, Calcium,
Magnesium, Manganese, iron, Zinc, Copper, Cobalt.
Conditions for Growth
a. Temperature: Microorganisms could be classified as:
i. Psychrophiles: they are able to grow at 0˚C or lower, though they grow at
higher temperatures (15˚-20˚C).
ii. Mesophiles: they grow within temperature range of approximately 25˚-40˚C.
iii. Thermophiles: they grow at temperatures between 45˚ – 60˚C. There are
some extreme thermophiles that can withstand temperatures about 100˚C e.g
Thermus aquaticus.
Optimum temperature is the temperature of incubation which allows for most rapid
growth during a short period of time (12 to 24 h).
b. pH:
i. Acidophiles: they grow at acidic pH
ii. Neutrophiles: they grow at neutral pH
iii. Alkalophiles: they grow at basic/alkaline pH
For most bacteria, the optimum pH for growth ranges from 6.5 – 7.5.
c. Oxygen Requirement:
i. Aerobes: grow in the presence of free oxygen
ii. Anaerobes: grow in the absence of free oxygen
iii. Facultative anaerobes: grow either in the presence or absence of free oxygen.
iv. Microaerophiles: grow in the presence of minute quantities of free oxygen.
, d. Additional requirements:
i. Halophiles: grow only in medium with unusually high concentration of salt
(10-15%) found in brines, salt packs, ocean water and certain foods.
2. Role of microorganisms in nature
How they affect people, property and the environment
Microorganisms are widely distributed in the different habitats available in nature. They are
carried by air currents from the earth’s surface to the atmosphere. They are found in seas
and oceans and they can be transported to high altitudes. They are carried by streams and
rivers and found at ocean depths and sea beds. Microorganisms are found abundantly in the
soil too.
Microorganisms occur abundantly where they find nutrients, moisture and conditions
conducive for their growth and reproduction. These conditions are prevail everywhere
around places humans inhabit and that’s why microorganisms are found in the air we
breathe, food we eat, on body surfaces, alimentary canal, mouth, nose etc.
Microorganisms can be found in very harsh environments where other life forms could not
be found such as salt lakes which have high concentrations of salt and thermal vents which
are characterised by exceptionally high temperature.
Microorganisms play several roles in nature that has a wide range of effects on man and the
environment, which could be advantageous or detrimental.
Some of the beneficial roles microorganisms play are as follows:
a. In the production of antibiotics
b. Production of fermented foods: improved flavours and texture in foods
c. Bioleaching of metal from ores
d. Production of alcoholic beverages
e. Production of milk-based products
f. Production of organic acids
g. Production of amino acids and enzymes
h. Remediation of oil spills
i. Biodegradation of sewage
j. Biogas production
k. Production of bio-fertiliser
l. Production of microbial pesticides
m. Production of vaccines
Detrimental roles of microorganisms
a. Deterioration of food/Food spoilage
b. Food borne diseases
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