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Microbial Distribution
- The presence of microbes in the environment is largely determined by their metabolism and ability to acquire necessary nutrients.
- Most microbes remain uncultured, highlighting the concept of "microbial dark matter."
- Microbes often exist in groups, relying on each other's metabolic processes, leading to complementary metabolisms.
Philosophical Perspective
- There are no intrinsically "good" or "bad" microbes; their primary goal is survival and replication.

After attending the lecture, students will be able to:

Define key terminology.
Explain how deep-sea vent ecology aids our understanding of the biosphere's formation.
Define the Deep Biosphere.
Describe the role of microbes in the carbon cycle.
Explain sulfate generation by microbes and its significance.
Outline the five major steps in the nitrogen cycle, detailing starting and ending products and significance of nitrate.
Discuss nitrogen fixation in various oxygen conditions, particularly by Rhizobium species.
Describe soil microbes' roles in the phosphorus cycle, especially in relation to Lake Champlain.
Understand the impacts of climate change and ocean microbial biomass on acidification.

Anoxygenic Photosynthesis: Uses sunlight for energy to convert CO₂ into organic compounds, coupled with the oxidation of elemental sulfur or hydrogen sulfide, typically in anaerobic conditions.
Chemosynthetic Microbes: Obtain energy from the oxidation of inorganic chemicals such as sulfur, typically found in deep hydrothermal vents.
Chemoautotrophic: Microbes that obtain energy through chemosynthesis.
Photoautotrophic: Microbes that derive energy from photosynthesis, using CO₂ as their main carbon source.
Eutrophication: The process involving excessive nutrient enrichment in bodies of water leading to dense algal blooms, oxygen depletion, and negative impacts on aquatic life.

Abiogenesis: Refers to the emergence of life from non-living matter.
- The first 3.8 billion years saw Bacteria and Archaea as the dominant life forms.
Primordial Environment:
- Atmospheric Composition: CO₂, NH₃, N₂, H₂, CH₄, HCN, H₂S, CO, H₂O.
- Ocean Composition: Presence of H₂S and Fe²⁺.
- Temperature Fluctuation: Ranged from approximately 100°C to glacial conditions.
- Factors for Chemical Synthesis: Heat, UV radiation, and lightning may have catalyzed amino acid formation in an organic geochemical broth.
Photosynthesis in Early Conditions:
- Anoxygenic photosynthesis likely thrived in anoxic conditions, converting:
  $6CO₂ + H₂S <br>ightarrow C<em>{6}H</em>{12}O_{6} + 6H₂O + 12S$
- This was mediated by anaerobic organisms similar to present-day photosynthetic bacteria, predating oxygenic photosynthesis.

Research on Deep Sea Vents:
- Deep-sea thermal vents, discovered in 1977, are utilized by scientists to study life's origins.
- Superheated water is expelled carrying various elements, minerals, and heavy metals, leading to a thriving ecosystem.
Microbial Ecosystems:
- Chemosynthetic bacteria establish microbial mats, the foundation of ecosystems around these vents, mainly belonging to Gammaproteobacteria and Epsilonproteobacteria.
- Environmental Conditions:
- Pressure: High, approximately 400 bar (395 atm).
- Temperature: High, between 150-400°C.
- pH: Low, around 3-5.
- Depth: Ranges from 2000 to 7,700 meters.

Formation of Stromatolites:
- Created by cyanobacteria through the secretion of EPS (extracellular polymeric substance) which traps sediments and forms a protective biofilm.
- Fossilized microbial mats serve as records of ancient life, with some dating back ~3.4 billion years.
Photosynthetic Activity:
- Cyanobacteria produce carbohydrates and O₂ through photosynthesis.
- In low light, purple sulfur bacteria utilize H₂S and near-infrared radiation for anoxygenic photosynthesis, leading to elemental sulfur production.
- Anaerobic sulfate-reducing bacteria further reduce SO₄²⁻ to H₂S.

Concept of Deep Biosphere:
- It was proposed in 1998 that one-third of Earth’s biomass carbon resides beneath the ocean floor; microbial communities (mainly Archaea) dominate this environment.
- At depths of 1 km, sediment samples can contain over 1 million intact cells per ml, demonstrating high microbial diversity despite slow metabolic rates reliant on sulfate/nitrate reduction or methanogenesis.
Significance of RNA Transcripts:
- Identifying RNA transcripts related to flagella, lipids, and ATP production emphasizes the complexity of life forms found in the deep biosphere.

Oxygen Cycle: Composed of contributions from plants and cyanobacteria, totaling 50% each.
Water Cycle: Integral to environmental health and nutrient cycle.
Carbon Cycle: Critical for sustaining life.
Nitrogen Cycle:
- Comprises five major steps: nitrogen fixation, nitrification, denitrification, and assimilation processes.
- Nitrate generated is crucial for plant nutrients, with 70% of nitrogen fixation performed by bacteria.
Phosphorus Cycle:
- Limited bioavailability poses challenges for ecosystems; microbial activity plays an essential role in making phosphorus accessible to plants.
Sulfur Cycle:
- Key for many metabolic processes, especially in microbial communities that perform anoxygenic photosynthesis.

Impact of Ocean Acidification:
- Projected drop in seawater pH by 0.2-0.4 units by 2100 due to increased atmospheric CO₂ levels.
- Changes in microbial community structures and functions impact calcification processes, nitrogen fixation, and exacerbated coral bleaching events.

Functions of Environmental Microbes:
- Critical roles include nutrient recycling, environmental refreshing, waste cleanup, and connection to broader life processes.
- The idea of Earth as a single organism reliant on finite resources dependent on microbes for sustainability is highlighted.

Rumen Microbiota:
- Essential for digestion, converting non-protein nitrogen into usable forms, producing volatile fatty acids, and synthesizing peptides/amino acids vital for livestock.
Impact of Antimicrobials in Agriculture:
- Significant usage in livestock can lead to microbial resistance and environmental contamination.
- Antimicrobial residues persist in the environment, affecting soil and water ecosystems.

Emphasis on understanding microbial roles aids in addressing ecological and health-related challenges posed by a changing environment.