Microbiology 221: Microbial Ecology

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Microbial ecology

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the interactions of microorganisms with each other and the environment around them

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population

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collection of similar organisms

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community

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mixture of interacting populations

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ecosystem

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the microbial community and its immediate environment

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niche

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what an organism does. interactions that an organism has with all the biotic and abiotic factors in its environment.

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Microbial interactions- positive effects

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Mutualism: +/+
Protocooperation: +/+
Commensalism: +/0

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Microbial interactions- negative effects

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Predation: +/-
Parasitism: +/-
Amensalism: -/0
Competition: -/-

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Mutualism (symbiosis), example

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-Obligatory relationship that is beneficial to both organisms

Example:
-Fungus (mycobiont) provides structure, environmental protection, water and minerals to the algae or cyanobacteria
-algae or cyanobacteria (phycobiont)- a photoautotroph provides organic carbon and other nutrients to the fungus.
-neither of these organisms could survive alone in this habitat.

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Protocooperation (Synergism, example

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-non-obligatory relationship that is beneficial to both organisms.

example:
-Desulfomonile reduces 3-chlorobenzoate to benzoate, which BZ-2 can use as food.
-BZ-2 respires H2 and CO2, which can be converted to methane by Methanospirillum sp., which produces vitamins for Desulfomonile teidjel.

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Syntrophy, example

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-A type of mutualism or protocooperation in which 2 or more different organisms can together degrade some substances that niether could degrade alone.

Example: Interspecies H2 transfer

-anoxic oxidation of CH4 is not favorable unless H2 concentrations are kept very low
-the sulfate reduces need H2 as a source of electrons
-together they can both derive energy from CH4 oxidation that neither could sustain alone

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Commensalism, example

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-Relationship in which one organism benefits while the other is niether harmed nor helped (a one way process)
-examples: bacteria that use the waste products of other bacteria as a substrate. Bacteria can benefit from the environmental changes of others

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Predation

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-The relationship in which one organism (the predator) benefits by attacking and often consuming another organism (the prey)

Example:
-protozoan ciliates (Paramecium) are active predators and bacteria are their prey
-predator prey population dynamics often exhibit a classic oscillatory behavior.

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Lotka-Volterra predator-prey equations

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-explains the oscillatory behavior of predator-prey dynamics

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Parasitism

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-relationship in which the parasite benefits by obtaining nutrients or reproductive capability from the host without killing it.

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Facultative parasites

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Parasites that can live as individuals without a host (ex. Legionella pneumophila, mycoplasma)

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Obligate parasites

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parasites that depend on a host cell to live or reproduce (viruses, Rickettsia)

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Parasites vs. Predators

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Features of predators:
1. brief contact with prey
2. live free of prey
3. usually larger than prey
4. not limited in range of prey species

Features of paracites:
1. prolonged contact with host
2. continually feed on host
3. usually smaller than host
4. often limited to a narrow range of host species.

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Amensalism, example

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-Relationship in which 1 organism has a negative effect on another (a 1 way process).
-Common example is the microbial production of antibiotics and antifungals

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Competition, example

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-Different organisms with in a population or community try to acquire the same resource.
-the resource can be the same space or nutrient.

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Competitive exclusion principle

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-If 2 species compete for exactly the same limited resource, one will succeed and one will decline. No 2 species can occupy the same niche and be stable.

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Niche heterogeneity

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Complex environments are filled with complex communities. Niche heterogeneity may be due to physical heterogeneity or substrate (chemical) heterogeneity.

Examples: activated sludge, soil particles

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homeostasis

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the capacity to maintain a stable community structure in response to environmental purturbations.

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Reductionism

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clockwork view of the world- mechanical.
All natural phenomena can be described by simple elegant equations

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Complexity

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-not easily understand, best defined by identifying what is lacking in current approaches to mode nature with "governing equations".
-many complex processes occur spontaneously in nature in the absence of any apparent central governing control mechanism

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Complex adaptive systems

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-Complexity theory typically deals with systems with hundreds of thousands of interacting parts and tries to understand the collective emergent properties of the dynamical behavior of such systems.

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Classic reductionist view vs. complexity view

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-reductionist: behavior is described by a governing mechanism
-complexity: emergent behavior. complex behavior arises from simple rules