Microbio Lecture 19 - PART 1

Symbiosis Types

• Mutualism:

  • Fungi (mycorrhizal) and plants form a mutualistic relationship.

  • Fungi deliver nitrogen, phosphorus, and water to plants.

  • Plants fix carbon and provide nutrients to the fungus.

  • Benefits both parties; fungi cannot survive independently of the plant.

Mycorrhizal Fungi and Plant Growth

• Plants grow better with mycorrhizal fungi compared to without.

• Fungi connect the roots of different plants, enabling nutrient sharing in forests.

• Large fungal colonies can represent the largest living organism on Earth.

Microbial Metabolism and Symbiosis

• Metabolism is a foundation of symbiotic interactions (e.g. Hawaiian bobtail squid, syntrophy).

• Relationships depend on chemical communication.

• Examples: Plant nodulation and the human microbiome.

Root Nodules Formation

• Leguminous plants (e.g., soybeans, clover) can fix nitrogen through a partnership with bacteria.

• Nodules contain nitrogen-fixing bacteria.

• Specific types of rhizobia are attracted and selected by plants.

• Plants secrete nutrients in the rhizosphere to favor specific rhizobia growth.

Nitrogen Fixation

• Nitrogenase enzyme is crucial for nitrogen fixation and is sensitive to oxygen.

• Plants provide controlled oxygen to the nodule using leg hemoglobin.

• Specific chemical signals (flavonoids and nod factors) ensure correct host-microbe interactions.

Human Microbiome

• Less diverse than environmental microbiomes.

• Important functions: digestion, immune system interaction, disease protection, vitamin production, and impacting behavior and brain function.

• Most research focuses on gut microbiome, primarily in the large intestine.