Microbial Nutrition

Essential Nutrients

Microorganisms require specific nutrients for growth, metabolism, and cellular structure. These nutrients are classified based on their quantity requirements and roles in the cell.

• Essential nutrient: Any substance that must be provided to an organism for survival and growth.

• Macronutrients: Required in large quantities; crucial for cell structure and metabolism.

  • Examples: Carbon (C), Hydrogen (H), Oxygen (O)

• Micronutrients: Needed in smaller amounts; involved in enzyme function and protein structure maintenance.

  • Also called trace elements

  • Examples: Manganese (Mn), Zinc (Zn), Nickel (Ni)

Categorizing Nutrients by Carbon Content

• Inorganic nutrients: Do not contain both C and H; found in earth's crust, water, atmosphere.

  • Examples: Magnesium sulfate, ferric nitrate, sodium phosphate, oxygen, carbon dioxide, water

• Organic nutrients: Contain both C and H; usually products of living things.

  • Examples: Methane, carbohydrates, lipids, proteins, nucleic acids

Chemical Analysis of the Microbial Cytoplasm

• Water comprises about 70% of all cellular components.

• Organic compounds make up 97% of dry cell weight.

• Elements CHONPS (Carbon, Hydrogen, Oxygen, Nitrogen, Phosphorus, Sulfur) account for 96% of dry cell weight.

• Most elements are available as compounds, not pure elements.

• A few nutrient types enable synthesis of thousands of cellular compounds.

Chemical Composition of E. coli

Microbial Nutrition: Carbon and Energy Sources

Key Terms

• Heterotroph: Obtains carbon from organic sources.

• Autotroph: Uses inorganic CO2 as carbon source; can convert CO2 into organic compounds.

• Phototroph: Derives energy from sunlight via photosynthesis.

• Chemotroph: Obtains energy from chemical compounds.

Nutritional Categories of Microbes

Autotrophs and Their Energy Sources

• Photoautotrophs: Photosynthetic; produce organic molecules using CO2.

• Chemoorganic autotrophs: Use organic compounds for energy, inorganic for carbon.

• Chemolithoautotrophs: Rely on inorganic minerals; do not require sunlight or organic nutrients.

Heterotrophs and Their Energy Sources

• Chemoheterotrophs: Obtain both carbon and energy from organic compounds; use cellular respiration or fermentation.

• Saprobes: Free-living decomposers; recycle organic nutrients from dead matter.

• Parasites: Derive nutrients from living hosts; may cause disease (pathogens).

  • Ectoparasites: Live on body surface

  • Endoparasites: Live in organs/tissues

  • Intracellular parasites: Live within cells

  • Obligate parasites: Cannot grow outside host

Essential Nutrients: Functions and Sources

Other Important Nutrients

• Potassium (K): Protein synthesis, membrane function

• Sodium (Na): Cell transport

• Calcium (Ca): Stabilizes cell wall and endospores

• Magnesium (Mg): Chlorophyll component, stabilizes membranes/ribosomes

• Iron (Fe): Cytochrome proteins in respiration

• Zinc (Zn): Regulatory element for eukaryotic genetics

Transport Mechanisms in Microbes

Diffusion and Osmosis

• Diffusion: Movement of molecules from high to low concentration.

• Osmosis: Diffusion of water across a selectively permeable membrane; water moves from high to low concentration until equilibrium is reached.

Cell Responses to Osmosis

Transport Processes in Cells

Active Transport

• Moves nutrients against the concentration gradient or faster than diffusion alone.

• Requires specific membrane proteins (permeases, pumps).

• Requires energy expenditure (ATP).

• Examples: monosaccharides, amino acids, organic acids, phosphates, metal ions.

Endocytosis

• Endocytosis: Cell engulfs substances by enclosing them in its membrane, forming a vacuole.

• Phagocytosis: Ingestion of whole cells or large solid matter (by amoebas, white blood cells).

• Pinocytosis: Ingestion of liquids or molecules in solution.

Concept Check

• An organism that derives its energy and carbon from organic molecules is a chemoheterotroph.

Temperature-Related Growth Capabilities

Cardinal Temperatures

• Minimum temperature: Lowest temperature for growth/metabolism; below this, activity stops.

• Maximum temperature: Highest temperature for growth/metabolism; above this, proteins denature.

• Optimum temperature: Promotes fastest growth/metabolism; intermediate between minimum and maximum.

Microbial Groups by Temperature Preference

• Psychrophiles: Optimum below 15°C; can grow at 0°C; rarely pathogenic.

• Psychrotrophs: Grow slowly in cold; optimum 15–30°C; Staphylococcus aureus and Listeria monocytogenes can grow at refrigerator temperatures.

• Mesophiles: Most medically significant microbes; grow at 20–40°C; human pathogens optimal at 30–40°C.

• Thermoduric microbes: Survive short high temperature exposure; usually mesophiles; include Bacillus and Clostridium.

• Thermophiles: Grow optimally above 45°C; found in volcanic soils, compost, sun-exposed habitats; extreme thermophiles grow at 80–121°C.

Ecological Groups by Temperature Range

Microbial growth rates vary with temperature, and different groups are adapted to specific ranges, as shown in growth curves (see referenced figure).

Additional info:

• These notes cover foundational concepts in microbial nutrition and growth, including nutrient classification, transport mechanisms, and temperature-related adaptations, which are essential for understanding microbial physiology and laboratory cultivation.