4/23/2025 Notes | BIOL 412

Topic: Symbioses

LEARNING OBJECTIVES

  • coevolution is a big claim to make

  • molecular mechanisms of interaction

  • classify symbioses based on their outcome

INTRO TO SYMBIOSES

  • 3-10 times microbial cells than human cells on the human body

  • 1/3 of metabolites in human blood are bacterial in origin

  • Symbioses: a prolonged and intimate relationship between two species

    • not necessarily positive; can be neutral, negative, or positive

    • can be microbe-microbe or microbe-macrobe

  • Microbiome: all microorganisms living in a particular environment through a particular span of time; can refer to organisms themselves or to their combined genetic material

  • Partnership Specificity: degree to which associations are strictly between two species, or allow for partner exchange

  • What is consortia?

  • Mutualism (+/+)

    • ex. lichens

      • fungi provides anchoring and protection

      • phototroph provides carbon source

      • ecological pioneers (colonize newly-disturbed land)

  • Metabolism and Nutrition (+/+)

    • sponges embed bacteria into epithelial cells to allow for greater nutrient uptake

    • ruminants and fermenters carry bacteria for many generations

    • cases study #1

      • insect associated microorganisms with restricted diets

      • defined diet experiments in aphids

      • depend on microbial organisms to derive animo acids and vitamins from sap

      • sources of microbial transmission

        • horizontal transmission via direct contact or environmental reservoir

        • vertical transmission via parent

      • genome reduction

        • high A-T content (up to 70%)

        • high mutation rates

        • 0.14-0.80 Mbp

      • bacteriome: specialized host organs

      • bacteriocytes: specialized host cells

  • Facilitation Commensalism (+/0)

  • Antagonism (+/-)

  • Parasitism (+/-)

  • Predation (+/-)

    • examples

      • filter feeders (sponges, clams)

      • detrivores (fiddler crab)

      • bacterivores (protozoans)

    • examples above are not prolonged, so not symbiosis

    • ex. bacterial parasite on tomato plant

      • symbiosis

  • Amensalism (0/-)

  • Competition (-/-)

  • When did microorganisms first interact with plants/animals?

    • from the very beginning of multicellularity

    • choanoflagellates (early “animals”)

      • multicellularity is induced by secretion of sulfonolipids by bacteria

    • land plants

      • fossils of plant-microbe associations

      • patterns of association across plant lineages

      • nutrients in soil derived from metabolic capabilities of bacteria and extended reach of hyphae

ANIMAL-MICROBE INTERACTIONS

  • animals evolved in a microbial world

  • ex.

    • termites

    • bobtail squid and Vibrio fisheri

  • look at Symbiosis slides for what to focus on in the textbook readings