Ch. 9 Microbial Growth

Nutrient

A nutrient is any substance that an organism requires for survival, growth, and reproduction. Nutrients are essential for metabolism and can include elements, compounds, and ions that bacteria need to form cellular structures and carry out metabolic processes.

Macronutrients

Macronutrients are required in large quantities and are critical for building cellular structures and energy production. Examples include: Carbon (C), Nitrogen (N), Phosphorus (P), Sulfur (S), and Oxygen (O).

Micronutrients

Micronutrients are required in small amounts but are still crucial for enzyme activity and metabolism. Examples include: Iron (Fe), Magnesium (Mg), Zinc (Zn), and Copper (Cu).

Examples of macronutrients

Carbon (C): Found in organic compounds or CO₂. Nitrogen (N): Obtained from organic compounds (proteins, nucleic acids) or from atmospheric nitrogen (N₂). Phosphorus (P): Important for ATP, nucleic acids. Sulfur (S): Found in sulfur-containing compounds like sulfates or hydrogen sulfide. Oxygen (O): Required for aerobic respiration.

Examples of micronutrients

Iron (Fe): Used in electron transport and cytochrome synthesis. Magnesium (Mg): Important for stabilizing structures like ribosomes and for enzyme activation. Zinc (Zn): Functions as a cofactor in enzyme activity. Copper (Cu): Used in respiratory enzymes and electron transport.

CHNOPS

Carbon (C): Obtained from organic compounds (heterotrophic) or CO₂ in the atmosphere (autotrophic). Hydrogen (H): Comes from water (H₂O) or organic compounds. Nitrogen (N): Acquired from atmospheric nitrogen (N₂) via nitrogen fixation or from organic nitrogen in amino acids. Oxygen (O): Available from water (H₂O) or atmospheric oxygen (O₂). Phosphorus (P): Obtained from inorganic phosphates (PO₄³⁻). Sulfur (S): Sourced from sulfur-containing compounds like hydrogen sulfide (H₂S) or sulfates (SO₄²⁻).

Role of trace elements

Trace elements are vital for bacterial metabolism. They are typically needed in small amounts but act as cofactors for enzymes, enabling them to catalyze biochemical reactions. For example: Iron (Fe) is used in respiration and electron transport. Zinc (Zn) is a cofactor for many enzymes, including those involved in DNA synthesis and protein synthesis. Copper (Cu) is involved in redox reactions.

Autotroph

An autotroph is an organism that produces its own food from inorganic substances using light or chemical energy. Types: 1. Phototrophs: Use light as an energy source (e.g., cyanobacteria). 2. Chemotrophs: Use inorganic chemicals (such as hydrogen sulfide or ammonia) as an energy source (e.g., nitrifying bacteria, sulfur bacteria).

Heterotroph

A heterotroph is an organism that obtains its carbon and energy by consuming organic compounds produced by other organisms. Types: 1. Saprophytes: Obtain nutrients from decaying organic matter (e.g., fungi, decomposers). 2. Parasites: Live off a host and often cause harm to it (e.g., Plasmodium causing malaria). 3. Commensals: Live in close association with a host but do not harm it (e.g., Lactobacillus in the human gut).

Psychrophiles

Psychrophiles are microorganisms that thrive in very cold temperatures (0-20°C), e.g., Psychrobacter.

Mesophiles

Mesophiles grow at moderate temperatures (20-45°C), including many human pathogens, e.g., Escherichia coli.

Thermophiles

Thermophiles thrive in higher temperatures (45-70°C), e.g., Thermus aquaticus.

Hyperthermophiles

Survive and grow at extremely high temperatures (70-100°C), e.g., Thermococcus species.

Obligate Aerobes

Require oxygen for growth (e.g., Mycobacterium tuberculosis).

Obligate Anaerobes

Cannot survive in the presence of oxygen (e.g., Clostridium botulinum).

Facultative Anaerobes

Can grow with or without oxygen, prefer oxygen but can switch to anaerobic processes if necessary (e.g., Escherichia coli).

Microaerophiles

Require low oxygen concentrations (e.g., Campylobacter jejuni).

Aerotolerant Anaerobes

Do not require oxygen but can tolerate it (e.g., Lactobacillus).

Acidophiles

Thrive in acidic environments (pH 0-5) (e.g., Ferroplasma).

Neutrophiles

Prefer neutral pH (pH 6-8), common in many bacteria including human pathogens (e.g., Escherichia coli).

Alkaliphiles

Grow in alkaline conditions (pH 9-11), e.g., Bacillus alcalophilus.

Halophiles

Require high salt concentrations (3-10% NaCl), e.g., Halobacterium.

Halotolerant

Can tolerate high salt concentrations but don't require them, e.g., Staphylococcus aureus.

Barophiles (Piezophiles)

Thrive in high-pressure environments (e.g., deep-sea bacteria).

Barotolerant

Can survive under higher pressures but do not require them.

Biofilms

Communities of microorganisms that stick to surfaces and are surrounded by a protective layer of extracellular polymeric substances (EPS). They provide protection to bacteria from environmental stresses, antibiotics, and the immune system.

General-purpose media

Supports growth of a wide range of bacteria (e.g., nutrient agar).

Selective media

Allows only certain types of bacteria to grow while inhibiting others (e.g., MacConkey agar).

Differential media

Differentiates bacteria based on metabolic properties (e.g., lactose fermentation) (e.g., EMB agar).

Enriched media

Provides extra nutrients for fastidious bacteria (e.g., blood agar).

Streak plate method

A technique to isolate individual colonies for obtaining a pure culture.

Binary fission

The process by which a bacterial cell divides into two identical daughter cells.

Generation time

The time it takes for a bacterial population to double in number, which can vary widely depending on species and environmental conditions (e.g., E. coli can double in 20 minutes under ideal conditions).

Lag phase

Bacteria are metabolically active but not dividing yet, preparing for growth.

Exponential (Log) phase

Rapid cell division and exponential growth.

Stationary phase

The rate of bacterial growth equals the rate of cell death due to nutrient depletion and waste accumulation.

Death phase

Cells die faster than they reproduce, and population size decreases.

Growth curves

Help scientists understand bacterial behavior under different conditions, such as nutrient usage, growth rates, and responses to antibiotics or environmental stress.

Direct methods

Counting bacterial cells under a microscope (e.g., using a Petroff-Hausser chamber), performing colony counts from plate counts.

Indirect methods

Measuring the turbidity of a culture (optical density) using a spectrophotometer, measuring metabolic activity, or gas production.