Prokaryote Metabolism and Ecology: Videos & Practice Problems

Dig Deeper into Prokaryotic Metabolism

Prokaryotic metabolism refers to the diverse ways microorganisms obtain energy, electrons, and carbon to grow and survive.

Key Terminology

• Phototrophs: Organisms that obtain their energy directly from sunlight.
• Chemotrophs: Organisms that obtain their energy from chemical compounds in their environment.
• Lithotrophs: Organisms that supply their electron transport chain with electrons from reduced inorganic molecules, such as water or iron.
• Organotrophs: Organisms that supply their electron transport chain with electrons from organic molecules containing carbon and hydrogen, like glucose.
• Autotrophs: Organisms that fix inorganic carbon dioxide to produce their own organic molecules through processes like carbon fixation.
• Heterotrophs: Organisms that consume organic molecules to obtain carbon for building cellular components.
• Electron transport chain (ETC): A series of protein complexes that transfer electrons to generate energy for the cell.
• Aerobes: Microbes that require oxygen as the final electron acceptor in their electron transport chain and grow only in oxygen-rich environments.
• Anaerobes: Microbes that grow in environments with little or no oxygen and do not use oxygen as the final electron acceptor.
• Obligate aerobes: Organisms that absolutely require oxygen to survive and grow.
• Facultative anaerobes: Organisms that can grow with or without oxygen but grow better in its presence due to higher ATP production.
• Microaerophiles: Organisms that require low levels of oxygen because high concentrations are toxic to them.
• Obligate anaerobes: Organisms that cannot tolerate oxygen and grow only in its absence.
• Aerotolerant anaerobes: Organisms that grow equally well with or without oxygen, showing tolerance to both conditions.
• Biofilms: Communities of microbes encased in a sticky extracellular polymeric substance (EPS) composed of polysaccharides, proteins, glycoproteins, glycolipids, and lipids.
• Extracellular polymeric substances (EPS): The slime-like matrix secreted by microbes that encases biofilms and protects the community.
• Carbon fixation: The process by which autotrophs convert inorganic carbon dioxide into organic molecules.
• Inorganic molecules: Molecules that do not contain both carbon and hydrogen, such as water (H₂O) and iron (Fe).
• Organic molecules: Molecules containing carbon and hydrogen, such as glucose (C₆H₁₂O₆).

Real-World Applications

• Understanding microbial metabolism helps in medical microbiology, such as targeting obligate aerobes like Mycobacterium tuberculosis, which require oxygen to cause lung infections.
• Biofilms are important in healthcare and industry because they can form on medical devices or pipes, leading to persistent infections or biofouling; studying their EPS matrix aids in developing strategies to prevent or disrupt them.
• Microbial classification based on energy, electron, and carbon sources guides environmental biotechnology, such as using chemolithotrophs in bioremediation to detoxify inorganic pollutants.

Common Misconceptions

• Not all microbes that use oxygen are the same; for example, facultative anaerobes can survive without oxygen but prefer it because it yields more energy.
• Phototrophs don’t just live in sunlight; some can also use organic or inorganic molecules as electron or carbon sources, showing metabolic diversity.
• Autotrophs don’t “eat” food like animals; instead, they fix carbon dioxide to build their own organic molecules, which is different from heterotrophs that consume organic carbon.
• Biofilms are not just random clumps of bacteria; they are highly organized communities protected by a complex extracellular matrix that helps microbes survive harsh conditions.
• Oxygen is not always beneficial; for some microbes like obligate anaerobes, oxygen is toxic and prevents their growth entirely.