Chapter 19 Microbial Interactions - BIOL 3340

Symbiosis

An association of two or more different species of organisms.

Ectosymbiont

Organism located on surface of another (usually larger) organism.

Endosymbiont

Organism located within another organism.

Symbiont

Any organism that has a specific relationship with another that can be characterized as mutualism, cooperation, or commensalism.

Mutualism

Some reciprocal benefit to both partners; relationship with some degree of obligation.

Microorganism-insect mutualisms

Endosymbiotic microbe provides needed vitamins and amino acids; insect host provides secure habitat and nutrients.

Aphid-Buchnera aphidicola interaction

Bacteria provides aphids the 10 essential amino acids absent from their sap diet; inability of these organisms to grow separately indicates co-evolution.

Protozoan-Termite relationship

Termite provides food for protozoan; protozoan digests cellulose in wood particles, providing nutrients for termite.

Zooxanthellae Mutualism

Marine invertebrates harbor zooxanthellae; dinoflagellates provide organic carbon to host.

Coral bleaching

Loss of either the photosynthetic pigments from the zooxanthellae or the complete expulsion of the dinoflagellates; caused by temperature increase.

Sulfide-Based Mutualism

Tube worm-bacterial relationships that exist thousands of meters below ocean surface.

Chemolithotrophic bacterial endosymbionts

Live within specialized organ (trophosome) of host tube worm; fix CO2 with electrons provided by H2S.

Rumen

Upper part of the ruminant stomach; contains large, diverse population of microbes.

Ruminants

Ruminant and microbial community have a mutualistic relationship.

Methanogenic archaea

In cows, CO2, H2, and acetate are used by methanogenic archaea to generate methane (CH4).

Methanogens

Methanogens synthesize many of the vitamins needed by their animal host, and they efficiently remove H2.

Cooperation

Benefits both organisms in relationship.

Cooperative relationship

Differs from mutualism because cooperative relationship is not obligatory.

Commensalism

One organism benefits and the other is neither harmed nor helped.

Commensal

Organism that benefits.

Examples of Commensalism

Microbial succession during spoilage of milk; Fermenting bacteria promote growth of acid-tolerant species; Formation of biofilms; Initial colonizer helps other microorganisms attach.

Amensalism

Negative impact of one organism on another based on release of a specific compound.

Antibiotic production

Antibiotic production by fungi and bacteria inhibits or kills other microorganisms.

Attine ants

Attine ants cultivate a garden of fungi belonging to the genus Leucocoprinus; dependent upon actinobacteria in the genus Pseudonocardia that produce inhibitory compounds that prevent the growth of Escovopsis spp.

Predation

Among microbes involves a predator species that attacks, usually killing its prey.

Vampirococcus

Vampirococcus has an epibiotic mode of attacking prey.

Daptobacter

Daptobacter penetrates prey then directly consumes the cytoplasmic contents.

Bdellovibrio

Bdellovibrio penetrates cell wall, grows outside plasma membrane.

Myxococcus

Myxococcus cells use gliding motility to creep, overtake their prey, and release degradative enzymes.

Parasitism

One organism gains (parasite) and the other is harmed (host).

Mycobiont

Fungal partner that provides water, minerals, sheltered environment, and firm substratum for growth.

Phycobiont

Alga or cyanobacterial partner that provides organic carbon and oxygen.

Genomic Reduction

Outcome of long-term parasitic relationship where the parasite loses unused genomic information.

Competition

Occurs when two organisms try to acquire or use the same resource.

Competitive exclusion principle

One organism dominates.

Resource sharing

Two organisms share the resource and both survive at lower population levels.