Microbiology of the Built Environment — Metal Leaching, Bioremediation, and Water Treatment Explained | Chapter 22 from Brock Biology of Microorganisms

How do microbes influence our built environments, from water systems to industrial sites and even the air we breathe indoors? Chapter 22 of Brock Biology of Microorganisms uncovers the fascinating world of environmental microbiology—revealing both the risks and rewards of microbial activity in human-designed spaces. Whether you're preparing for AP Biology or deepening your scientific understanding, this comprehensive guide summarizes key processes and concepts explored in the chapter.

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Microbial Leaching and Acid Mine Drainage

Certain bacteria and archaea can extract valuable metals from low-grade ores—a process called microbial leaching. Species like Acidithiobacillus ferrooxidans facilitate copper, uranium, and gold recovery by oxidizing metal sulfides in large leach dumps. While this boosts metal production, improper pyrite handling can trigger acid mine drainage, a major environmental issue that acidifies water and leads to iron precipitation. The dominant microbes vary with temperature and can include Archaea such as Sulfolobus.

Bioremediation of Environmental Pollutants

Microorganisms are nature’s clean-up crew. Bioremediation uses aerobic and anaerobic bacteria to degrade harmful substances:

• Hydrocarbon degradation: Bacteria like Alcanivorax break down oil and fuel.
• Uranium cleanup: Genera such as Shewanella, Geobacter, and Desulfovibrio convert soluble uranium to an insoluble form.
• Chlorinated compounds: Dehalococcoides species dechlorinate pollutants like PCE and TCE.
• Plastic biodegradation: Ideonella sakaiensis produces enzymes (PETase and MHETase) that break down PET plastics.

Bioremediation offers promising solutions for cleaning up oil spills, toxic waste, and persistent plastics.

Wastewater Treatment: Microbial Management for Public Health

Wastewater treatment relies heavily on microbial processes:

• Primary Treatment: Physically removes large solids.
• Secondary Treatment: Uses activated sludge and trickling filters for microbial breakdown of organic material.
• Tertiary Treatment: Eliminates excess nutrients like phosphorus (using PAOs) and nitrogen (via nitrification and denitrification).
• Advanced Techniques: Methods like anammox and aerobic granular sludge make treatment more compact and efficient.

Digesting sludge can even produce methane as a renewable energy source. However, emerging contaminants like pharmaceuticals are challenging to remove, highlighting ongoing innovation in the field.

Drinking Water Treatment and Microbial Risks

Ensuring safe drinking water involves several treatment steps:

• Sedimentation, coagulation/flocculation, filtration, and disinfection.
• Chlorination remains a standard for residual protection, while UV disinfection offers a chemical-free alternative.
• Biofilms in distribution pipes may harbor microbes such as Mycobacterium, Legionella, and Pseudomonas. Opportunistic pathogens can be protected by protozoa within these biofilms.

Ongoing monitoring is crucial to protect public health.

Indoor Microbial Ecology: The Built Microbiome

Modern buildings—from homes to subways—are teeming with diverse microbial communities. These microbiomes are shaped by humans, pets, and even the air, with molecular tools revealing unique "fingerprints" left by occupants. Cleaning practices and the use of antimicrobials alter the balance of indoor microbes. Plumbing fixtures, such as toilets and showerheads, serve as important microbial reservoirs.

Microbially Influenced Corrosion (MIC) and Infrastructure

Microbial activity can also damage infrastructure. In anoxic (oxygen-poor) conditions, microbes accelerate corrosion of buried metals:

• Sulfate-reducing bacteria produce hydrogen sulfide (H₂S).
• Iron reducers and methanogens extract electrons from metals.
• Fungi and bacteria secrete acids that degrade concrete, leading to problems such as crown corrosion in sewer pipes.

Understanding these processes helps engineers design more durable systems.

Glossary: Key Terms from Chapter 22

• Acid mine drainage: Acidic water produced from sulfide mineral oxidation.
• Bioremediation: Microbial cleanup of pollutants.
• BOD: Biological oxygen demand — oxygen used by microbes during decomposition.
• Chlorination: Water disinfection with chlorine.
• Anammox: Anaerobic ammonium oxidation in wastewater treatment.
• Flocculation: Clumping of particles for easier removal.
• PETase: Enzyme that breaks down PET plastics.
• MIC: Microbially influenced corrosion.
• Crown corrosion: Sulfuric acid degradation of sewer pipes.
• Bioaugmentation: Adding selected microbes to boost remediation.

Conclusion: The Importance of Environmental Microbiology

Chapter 22 demonstrates that understanding microbes in the built environment is essential for engineering sustainable cities, improving public health, and harnessing biotechnology for environmental cleanup. The intersection of microbiology and technology is opening new frontiers in resource recovery, water safety, and urban ecology.

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