Lecture Notes: Microorganisms in Aquatic Environments and Deep-Sea Vents

Overview

• Discussion includes the importance of microorganisms in aquatic environments and deep-sea ocean vents.
• Focus on energy utilization by microorganisms and the carbon cycle.

Microorganisms in Aquatic Environments

• Photosynthetic Bacteria: Includes Polygobacter ubique, which uses proteorhodopsin for energy.
• Energy in Oceans: Historically underestimated until rhodopsins were discovered.

Deep-Sea Ocean Vents

• Discovery: First discovered in 1977 by geologists.
• Environment Characteristics:
  • Volcanic activity between tectonic plates.
  • Temperatures range from 5 to 400°C.
  • pH varies from acidic to neutral.
  • Rich in hydrogen sulfide, methane, and other reduced compounds.
• Energy Source: Unlike surface ecosystems, energy is derived from Earth's core, not sunlight.

Available Chemistry in Deep-Sea Vents

• Inorganic Compounds: Used by chemoautolithotrophs for energy.
• Electron Acceptors and Donors: Oxygen, nitrate, nitrite (acceptors); hydrogen, ammonia, methane (donors).

Microorganisms in Deep-Sea Vents

• Sulfide Oxidizers: Convert hydrogen sulfide to sulfate.
• Methanogens: Use hydrogen gas to produce methane.
• Methylotrophs: Oxidize methane to CO2 and water.
• Examples:
  • Methanococcus jannaschii and Pyrococcus abyssi can grow at temperatures over 100°C.
  • Geoglobus ahangari uses iron as an electron acceptor.
  • Thermococcus atlanticus is a protein-metabolizing thermophile relevant to biotechnology.

Symbiotic Relationships

• Tube Worms: Engage in mutualistic relationships with bacteria; utilize CO2 and H2S via hemoglobin proteins.

The Carbon Cycle

• Origin of Carbon: Fusion in stars.
• Carbon Storage: 99.5% in rocks and sediments.
• Carbon Cycle Dynamics:
  • Pre- and post-industrial flux.
  • Microbial role in respiration and photosynthesis.

Carbon Fixation Pathways

• Calvin Cycle: Common in plants.
• Alternative Pathways: Reductive acetyl-CoA pathway (notably low ATP requirement).

Methylotrophs

• Function: Oxidize methane to CO2, leveraging an electron transport chain.
• Adaptations: Some can function anaerobically by using nitrite as an electron acceptor.

Global Carbon Cycle

• Anthropogenic Impact: Small but significant contribution to CO2 increase.
• Microbial Contribution: Significant in cycling carbon through photosynthesis and respiration.

Immune System Introduction (Not covered in detail but briefly introduced)

• Components: Physical barriers, innate and adaptive immunity.
• Misconception Addressed: Immune system presence outside circulatory system.