Microbial Growth and Nutritional Requirements

Study Notes

Microbial Growth

Microbial growth involves an increase in the quantity of cellular constituents, leading to an increase in cell number and population mass.
Microbial growth follows a specific pattern described by the microbial growth curve.
The generation time is the time it takes for bacteria to double in number during a specific time period.
The generation time varies depending on the type of bacteria.

Nutritional Requirements

Macronutrients are required in large amounts by microorganisms and are used to create carbohydrates, proteins, lipids, and nucleic acids. Examples include carbon, oxygen, nitrogen, hydrogen, phosphorus, and sulfur.
Micronutrients are required in small amounts and are often minerals that act as cofactors for enzymes. Examples include manganese, zinc, cobalt, molybdenum, nickel, and copper.
Some bacteria have symbiotic relationships with their hosts, where they benefit from the host while also contributing to the host's biological processes.
- Nitrogen-fixing bacteria in the root nodules of legumes convert atmospheric nitrogen into ammonia, providing the plant with a nitrogen source.
- Escherichia coli in the human alimentary canal help prevent harmful bacteria growth.
- Cellulose digesting bacteria in the alimentary canal of ruminants aid in digestion.
Parasitic bacteria live in the bodies of animals and plants, obtaining nutrients from their host. These bacteria can cause disease by exploiting the host or secreting toxins.

Energy and Carbon Sources

Photoautotrophs obtain energy from sunlight and use carbon dioxide as their carbon source for photosynthesis.
Photoheterotrophs obtain energy from sunlight but use organic compounds as their carbon source.
Chemoautotrophs use chemical energy from inorganic sources like CO2 to produce food.
Chemoheterotrophs use chemical energy from organic compounds like carbohydrates, proteins, and lipids to produce food.

Nitrogen Sources

Microorganisms can obtain nitrogen from organic sources (amino acids, peptides, proteins) or inorganic sources (ammonium salts, nitrates).
Nitrogen is used to synthesize proteins, amino acids, RNA, and DNA.
Nitrogen-fixing bacteria can directly convert atmospheric nitrogen into ammonia.

Growth Factors

Growth factors are required in small amounts and fulfill specific roles in metabolism.
Three main categories of growth factors:
- Purines and pyrimidines: used in nucleic acid synthesis.
- Amino acids: used in protein synthesis.
- Vitamins: used as coenzymes for certain enzymes.

Environmental Factors

Temperature is a crucial factor for microbial growth.
Different types of microorganisms have different temperature optima:
- Psychrophiles: thrive in cold environments (-20°C to +20°C).
- Mesophiles: thrive in moderate temperatures (20°C to 45°C).
- Thermophiles: thrive in high temperatures (45°C to 80°C).
- Hyperthermophiles: thrive in very high temperatures (70°C to 110°C).
Oxygen requirement varies depending on the type of microorganisms:
- Obligate aerobes: require oxygen for growth.
- Microaerophiles: require low oxygen concentrations for growth.
- Facultative anaerobes: can grow with or without oxygen.
- Aerotolerant anaerobes: can tolerate oxygen but do not use it for growth.
- Obligate anaerobes: cannot grow in the presence of oxygen.
pH also impacts growth:
- Acidophiles: thrive in acidic environments (pH 0 to 5.5).
- Alkaliphiles: thrive in alkaline environments (pH 7.5 to 14).
- Neutrophiles: thrive in neutral environments (pH 5.5 to 8).
Osmotic pressure, which is the pressure needed to prevent water movement across a semipermeable membrane, also influences growth:
- Isotonic solution: equal water and solute concentration inside and outside the cell.
- Hypertonic solution: higher water concentration inside the cell, leading to water loss.
- Hypotonic solution: higher water concentration outside the cell, leading to water gain.
Salt concentration also affects growth:
- Halophiles: require high salt concentrations for growth.
- Halotolerant: can tolerate high salt concentrations but do not require them for growth.