Lecture 6 - Exam 2: Interactions Among Microbial Populations Flashcards
What are positive versus negative interactions?
Positive: leads to increase growth rate and population size
Negative: reduced population size and slower growth rate
Interactions among microbial populations has to deal with what?
Population densities. When population density is low, there tends to be more positive interactions. When there is a high population density, then we get negative interactions (competing for resources)
Describe the effect of interaction of neutralism, commensalism, synergism (protocooperation), symbiosis (mutualism), competition, amensalism (antagonism), and predation & parasitism.
Neutralism: 0 & 0
Commensalism: 0 & +
Synergism: + & +
Symbiosis: + & +
Competition: - & -
Amensalism: 0 & -
Predation & Parasitism: + & -
Synergism (mutualism): The relationship between the two populations is __________. They have to have ______ partners.
Obligate ; fixed
What is the difference between predation and parasitism?
Parasitism contact time with its host is longer and can keep the host alive (or it can die). The parasite is usually smaller than its host. Predation contact time is shorter (lion eats rabbit). The size of the predator is usually larger than its prey.
If we have 0 for one population and + for the other is that considered a positive, neutral, or negative interaction?
What about if it is 0 and -?
Positive ; Negative
Describe neutralism.
Lack of interaction between populations. Can be separated by time or space. Ex: microbes at the top of the soil versus microbes in the lower soil profile.
Describe Commensalism.
One population benefits from the presence/activity of a second population but the other remains unaffected. Ex: Photosynthetic organism produces oxygen and that benefits aerobes in the soil.
Describe synergism.
(Protocooperation, syntrophy) Association of mutual benefit to both species, but without that cooperation being obligatory. Don’t have to be fixed partners in a relationship. Ex: The decomposition of organic material is important for the soil. We have one population breaking down one compound and produce another one, and then we have another population breaking down a product produced by the first population. Both populations can work together to completely break down the substrate.
Describe symbiosis (mutualism).
An obligatory relationship between two populations that benefits both populations. Ex: The relationship between the two populations are obligatory, Mycorrhizae (symbiosis between plants and fungi)
What are some symbiosis organism examples?
Mycorrhizae, Legume-rhizobium symbiosis, Actinorhizal symbiosis (involved actinobacteria and woody plants, together they fix nitrogen), Lichens, Leafcutter ants (bring back leaves to their nest but don’t eat them, they feed the fungus.
What are the three types of lichens and how are they classified?
Crustose, foliose, fruticose. They are based on their attachment to the substrate.
Describe each of three types: Crustose, Foliose, and Fruticose
Crustose: Firmly attached to their substrate
Foliose: Not as firmly attached, they sit up more on the rock
Fruticose: Fully standing up and develop short stalks… least attached to substrate.
Lichens are what type of indicators?
Lichens are sensitive ecological indicators… Sensitive to air pollution in cities… if tombstones are not covered in lichens then can be a sign of air pollution.
Describe competition.
A negative relationship between two populations in which both populations are adversely affected with respect to their survival and growth.
Describe amensalism (antagonism).
Growth of one population is restricted by presence of the second population, but the latter is not affected. Involves the chemical compounds (antibiotics, acids ethanol, bacteriocins).
Describe Predation and parasitism.
Direct attack and feeding of one population on the other.
In microbial world, these two things are kind “blurry.”
What are some examples of predation and parasitism?
Protozoa (the main predators in the soil) consume 100-1000 bacteria per hour.
Nematodes prey on bacteria, protozoa, fungi and smaller nematodes.
Nematode trapping fungi. They set up traps for moving animals. They then send in hyphae to digest the contents of the nematodes and small fauna.
Nematodes can catch fungi and there are two types. What are they?
Sticky knobs and sticky net. The fungi here don’t have a septum in their hyphae and they produce these gooey materials and nematodes passing by get stuck in them.
The other type is nonconstricting and constricting rings. It is a more complex trapping mechanism. Fungi with septum in their hyphae. Have three cells forming rings. Some of these rings are nonconstricting and stay in fixed shape. The constricting rings can sense coming through, and they close shut.
Bacterial predators include:
(more difficult to study due to their small size)
Agromyces ramosus, Myxobacteria, Bdellovibrio sp.
Describe Agromyces ramosus.
Catalase-negative actinobacteria and uses manganese complex to remove the reactive oxygen species.
Is non-obligate predator of G+ and G- bacteria, meaning it uses organic material as carbon source and attacks both types of bacteria.
Method of predation: Prey cells produce growth initiation factor and this organism can sense the GIF-Mg2+ complex and attack them.
Describe Myxobacteria.
Gram -, have gliding motility, non-obligate predator of G= and G-, excrete a lot of hydrolytic enzymes that help them digest food and G+ and G- cells, and have group predation (wolfpack strategy)
Describe Bdellovibrio sp.
(bdellovibrio means leech) Tiny vibroid, G-, obligate anaerobe, highly motile (can swim at a speed of 160um/sec), obligate predator for G- bacteria.
Describe the life cycle of Bdellovibrio bacteriovorus
Start as free swimming Bdellovibrio. They will attach to prey (5-10min), and will release an enzyme to lyse the cell wall and rotate to enter the host cell. They will then enter the periplasmic space (15 min) and will modify shape of the host (from rod to spherical) called a Bdelloplast. It will then use the contents of the host cells to become long filaments. These filaments will then divide to become more smaller pieces and then flagella is synthesized and then release hydrolytic enzymes and let themselves out of the host cell. THAT IS HOST DEPENDENT
HOST INDEPENDENT:
Once the the bdellovibrio exist the host cell, they will have an attack phase and free swimming. Then, they will have a nutrient medium and grow in biofilms or filamentous cells in liquid and then will become free swimming bdellovibrio again.
