Microbes are microscopic organisms, categorized into five groups: bacteria, fungi, viruses, protozoa, and algae. Microbial growth reflects changes in population through binary fission and requires specific physical and chemical factors, including temperature, pH, nutrients, and oxygen levels. The bacterial growth curve consists of four phases: lag, log/exponential, stationary, and death phases.

1. Microbial Growth

2. What are microbes??
• A microorganism, or microbe, is a microscopic organism, which may exist in its
single-celled form or in a colony of cells.
• There are 5 basic groups of microorganisms:
a. Bacteria
b. Fungi
c. Viruses
d. Protozoa
e. Algae

3. • Each type has a characteristic cellular composition, morphology,
mean of locomotion, and reproduction.
• Microbes are tiny living things that are found all around us and are
too small to be seen by the naked eye.
• They live in water, soil, and in the air.
• The human body is home to millions of these microbes, some of
which makes us sick, whereas some others are helpful too.

4. Growth??
• Growth in plants and animals is generally an increase in size.
• But, in microorganisms, particularly bacteria, growth, refers to change in
total population, rather than individual cells.
• This chiefly includes binary fission.
• A cell undergoing binary fission is immortal unless, it is deprived of
nutrients or subjected to various stress.
• Microbial growth occurs in a geometric progression.

5. Geometric Progression

6. Requirements for microbial growth
2. Chemical
• Carbon
• Nitrogen, Sulphur
and Phosphorous
• Trace elements
• Oxygen
• Organic growth
factors
1. Physical
• Temperature
• pH
• Osmotic Pressure

7. Physical Factors
1. Physical
• Temperature
• pH
• Osmotic Pressure

8. 1. Temperature
• Optimum temperature required
• Higher temperature: microbial membrane is disrupted
• Lower temperature: membrane solidifies
• 3 types;
1. Psychrophile: -20 to +10 °C eg; Oscillatoria, Chlamydomonas
2. Mesophile: 20 to 45 °C eg; E. coli, Streptococcus pneumoniae
3. Thermophile: 50 to 80 °C eg; Thermus aquaticus, Geogemma barosii

9. 2. pH
• Drastic variation in pH can disrupt the plasma membrane or inhibit
the activity of enzymes and transport proteins
• 3 types;
1. Acidophiles: 0 to 5.5 eg; Thiobacillus, Ferroplasma
2. Neutrophiles: 5.5 to 8 eg; E. coli, Lactobacillus
3. Alkalophiles: 7.5 to 14 eg; Thermococcus alcaliphilus

10. 3. Osmotic Pressure
• It is the minimum pressure which needs to be applied to a solution to
prevent the inward flow of its pure solvent across a semipermeable
membrane.
• Bacteria classified into 2 based on osmotic pressure;
1. Osmophiles: Grow at high sugar concentration eg; Saccharomyces
2. Halophiles: Grow at high salt concentration eg; Halobacterium

11. Chemical Factors
2. Chemical
• Carbon
• Nitrogen, Sulphur
and Phosphorous
• Trace elements
• Oxygen
• Organic growth
factors

12. • Bacteria are normally grown in culture media, where nutrients are
supplied in the form of a solution.
• The essential elements required for growth are usually supplied in
the form of water, macro/micro molecules, inorganic ions etc.
1. Carbon
2. Nitrogen, Sulphur and Phosphorous
3. Trace elements
4. Oxygen
5. Organic growth factors

13. 1. Carbon
• Classified as
1. Autotrophs: eg; Cyanobacteria
2. Heterotrophs: eg; Salmonella
2. Nitrogen, Sulphur and Phosphorous
• Required for synthesis of cellular material
• Nitrogen + Sulphur Protein Synthesis

14. • Nitrogen + Phosphorus Synthesis of DNA, RNA
• Nitrogen: 14% dry weight
• Sulphur and Phosphorous: 4% dry weight
3. Trace Elements
• Fe, Cu, Mo and Zn
• Required for the functioning of enzymes

15. 4. Oxygen
• Classified into 4 types;
1. Obligate aerobes: grows only in the presence of oxygen
2. Obligate anaerobes: grows only in the absence of oxygen
3. Facultative anaerobes: require oxygen but can survive in
absence of oxygen
4. Microaerophile: growth occurs only when oxygen is
diffused into the medium
5. Aerotolerant anaerobes:
exclusively anaerobic (fermentative) type of metabolism
but they are insensitive to the presence of O2
High
Low
Level of O2

16. 5. Organic Growth Factors
• Mainly of 3 types;
1. Purines and Pyrimidines: needed for synthesis of DNA and RNA
2. Amino acids: required for protein synthesis
3. Vitamins: needed as co-enzymes and functional group of certain
enzymes

17. Bacterial Growth Curve
• Consists of 4 phases;
1. Lag phase
2. Log/Exponential Phase
3. Stationary Phase
4. Death Phase

18. Summary
• Microbes
• Growth
• Geometric Growth
• Requirements needed for microbial
growth
• Bacterial Growth Curve

19. Thank You