Microbial Interactions - MicroCore Review Center

Which of the following is not true regarding Allee's Principle?

• Both positive and negative interactions may occur even within a single population

• Highly suitable for explaining density-independent interactions

• With increasing population density, positive interactions could theoretically increase the growth rate to some asymptotic limit

• Positive interactions predominate at low population densities and negative ones at high population densities

Answer explanation

According to Allee’s principle, both positive and negative interactions may occur even within a single population. Such interactions, originally observed on animals and plants, are interrelated and are population density dependent. Allee’s principle is highly suitable for explaining density-dependent interactions that occur between microbial populations.

Which of the following is not true regarding symbiosis?

• Interaction between populations existing in close association with each other

• May involve either unicellular or multicellular organisms

• Participants are not always represented at 1:1 ratio

• They are only positive interactions (such as mutualism), separate from amensalism.

• None of the aforementioned

Answer explanation

In symbiosis, both positive and negative interactions can occur. Image from: https://ib.bioninja.com.au/standard-level/topic-4-ecology/41-species-communities-and/species-interactions.html

Associations an be described in terms of the following, except:

• Durability

• Dependency

• Specificity

• Location

• None of the aformentioned

Answer explanation

Associations can also be described in terms of:

-dependency (obligate or facultative)

-durability (persistent or transient)

-specificity (specific or non-specific)

-location (ecto-living outside, endo-living within)

Which of the following is an example of cooperation?

• Marine nematode-bacteria

• Lichen

• Tube worm-bacteria

• Termite and cellulolytic microorganisms

• Flashlight fish and bioluminescent bacteria

Answer explanation

The bacteria protect the nematode by decreasing sulfide concentrations near the worm, and the worm uses the bacteria as a food source.

Mutualism is an obligatory microbial interaction where mutualist and host are metabolically dependent on each other. Cooperation is a non-obligatory microbial interaction where mutualist and host are not metabolically dependent on each other.

Choose the best answer. Which type of interaction is observed when the wasteproduct of one microorganism is the substrate for another species?

• Amensalism

• Mutualism

• Commensalism

• Cooperation

• Competition

Answer explanation

Commensalism is a low specificity relationship which displays a one-way positive exchange of materials.

Which of the following causes competition?

• Modification of the environment to make it more suited for another

• Abundance of resources

• Overlap in the niche

• Production of antimicrobials and metabolic products

Which of the following competitive phenotypes in microbes has an effect of disrupting other's competitive phenotype?

• Inhibit quorum sensing

• Type VI secretion systems (contact -dependent)

• Production of structural and motility molecules

• Siderophore secretion

• Digestive enzyme secretion

Which of the following is not true about predation?

• Predator engulfs or attacks the prey and normally results in the death of the prey

• It is density independent

• It requires the coexistence of the predator and prey

• Impacts both prey and predator

Answer explanation

Higher-density populations may attract predators who wouldn’t bother with a sparser population. When these predators eat individuals from the population, they decrease its numbers but may increase their own. Image from: https://www.khanacademy.org/science/ap-biology/ecology-ap/population-ecology-ap/a/mechanisms-of-population-regulation#:~:text=Predation.,but%20may%20increase%20their%20own.

Which is not an example of parasitism?

• Ascaris suum - pigs

• Yersinia pestis - humans

• Nostoc - fungi

• Ralstonia solanacearum - tomato

Answer explanation

Nostoc is by far the most common genus of cyanobacteria in lichens, especially in the temperate and cool regions of the world. The lichen symbiotic Nostoc genotypes are closely related to plant symbiotic and free-living forms of the same genus. Image from: Rikkinen J (2013) Molecular studies on cyanobacterial diversity in lichen symbioses. MycoKeys 6: 3-32. https://doi.org/10.3897/mycokeys.6.3869

What type of interaction exists between Methanospirillum and Desulfonomonile tiedjei?

• Cooperation

• Commensalism

• Competition

• Predation

• Mutualism

Answer explanation