Microbiology: Chapter 28
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- What determines whether associations are mutualistic, cooperative, or commensal?
- Classification by benefit determines whether an association is mutualistic (both parties benefit and need each other), cooperative (both benefit but not obligatory), or commensal (one org is helped while the other is neither helped nor harmed).
- Describe the termite-protozoan mutualistic relationship.
- A protozoan lives in the gut of termites. The termite ingests cellulose and lignin, which it cannot digest; the protozoan digests them and releases acetate (fermentation) which the termite lives off of.
- Describe the lichen mutualistic association.
- Ascomycete (mycobiont), a fungus, provides water and minerals while green or blue-green algae (phycobiont) provides oxygen, energy, other nutrients, and fixes carbon which feeds the fungus.
- Describe the zooxanthellae mutualistic association.
- Zooxanthellae are spherical algal cells harbored by marine invertabrates. Reef building corals get most of their energy from the endosymbiotic algae and provide pigments that protect the algae from harmful UV.
- Describe the mutualistic association of the hydro-thermal vent tube worm.
- The red gutless tube worm contains an endosymbiotic bacteria. Here is the relationship: the tube worm's gills absorb H2S, CO2, and O2; the vasculature transfers H2S bound to Hb to the body; the bacteria then oxidize H2S and use the H to fix CO2 for the worm to live off of.
- Describe the mutualistic association of the rumen.
- This occurs in the rumen of cows and some other animals; The ruminants ingest complex carbs which mix in the rumen with a complex microbial community. Bacterial fermentation occurs resulting in short-chain fatty acids, CO2, CH4, and vitamins, which the host utilizes.
- Which of the previous examples are endosymbiotic and which are ectosymbiotic relationships?
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Endosymbiotic: zooxanthellae, tube worm, lichens (?)
Ectosymbiotic: rumen, termite-protozoa - What is the basis for the relationship of Eubostrichus with its bacterial ectosymbiotes?
- The relationship between Eubostrichus dianae, nematode, and its ectosymbiotic bacteria is an example of cooperation; both benefit but not obligatory. The sulfide-oxidizing bacteria live on the outside of the nematode, decreasing levels of toxic sulfid. As the nematode moves around the bacteria gain nutrients and then later fall off and the nematode eats the nurtient rich bacteria.
- What determines whether associations are predative?
- In predative associations, the microbe attacks or engulfs the prey, which can be smaller or larger than itself, and this prey usually dies.
- What determines whether associations are parasitic?
- In parasitic associations, the microbe is helped while the host is harmed; the host must be much larger than the parasite and the association may lead to its death, however it may not.
- What determines whether associations are amensalistic?
- In amensalistic associations, one organism releases a specific compound that has a negative effect on another organism.
- What determines whether associations are competitive?
- In competitive associations, different microbes are 'competing' for the same resource(s).
- Give an example of each: predation, parasitism, amensalism, and competition.
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Predation: Bdellovibrio-penetrates bacterial host periplasm and grows up in now dead host; the cell is then lysed and the parasites progeny are released.
Parasitism: Corynebacterium diptheriae and Rhizophydium sphaerocarpum with algae.
Amensalism: Attine Ants-use antibiotic producing bacteria(Steprtomycetes) to control Escovopsis, an aggressive fungus that destroys the ants' funal gardens.
Competition: Competitive Exclusion Principle-when 2 orgs compete for the same limiting resource, one will exclude the other. - What processes are involved in nutrient cycling?
- Nutrient cycling is biogeochemical cycling, it involves both biological and chemical processes, oxidation-reduction reactions, and it involves both aerobic and anaerobi environments.
- What are the various roles of fermentation, respiration and carbon fixation in the carbon cycle?
- In the carbon cycle, fermentation forms CO2 and partially oxidized carbon compounds (ethanol, acetice acide). Respiration: Anaerobic respiration can form CH4 from CO2 (methanogenesis) and aerobic respiration fo CH4 forms CO2. Carbon fixation (by photoautotrophs or chemoautotrophs) converts CO2 into organic carbon that can then go through methanogenesis, respiration, or fermentation.
- What would be representative classes (defined by role, not taxonomy) of organisms for these processes?
- (?)Representative classes of organisms that perform the roles mentioned would be fermenters, respirers, and carbon fixers.
- What are the processes of mineralization and immobilization?
- Mineralization is the process in which excess organic matter is decomposed to release simpler, inorganic compounds (CO2, NH4+, CH4, H2). Immobilization is the incoporation of a simple, soluble substance into the bodyof an organism, making it unavailable for use by other orgs.
- How does assimilatory Sulfur reduction differ from dissimilatory Sulfur reduction?
- In assimilatroy Sulfur reduction, sulfate is reduced to incorporate it into organic material (used in biosynthesis of AAs/prots); no energy is made available. In dissimilatory Sulfur reduction (anaerobic), sulfate/sulfite is used as an electron acceptor and is reduced but not incorporated incorporated into organic matter during biosynthetic processes.
- How do aerobic sulfur oxidizers differ from anaerobic sulfur oxidizers in their use of the sulfur?
- Aerobic chemolithotrophic sulfur oxidizers (?)reduce sulfur for use in AA/prot biosynthesis, while anaerobic photolithotrophic sulfure oxidizers use sulfate as an external electron acceptor to form sulfide.
- What roles in the nitrogen cycle are played by nitrogen fixers?
- Nitrogen fixers (only proks) form organic nitrogen; nitrogenase conversion of dinitrogen to ammonium ions.
- What roles in the nitrogen cycle are played by denitrifying bacteria?
- Denitrifying bacteria (anaerobic) use nitrate as an electron acceptor and results in the production of nitrogen gas (N2) and nitrous oxide (N2O), although nitrite (NO2-) can also accumulate.
- What roles in the nitrogen cycle are played by nitrifying bacteria?
- Nitrifying bacteria (aerobic) oxidize ammonium ions (NH4+) to nitrite (NO2-) and oxidize this to nitrate (NO3-).
- What is the anammox reaction?
- The anammox reaction is a way that nitrogen gas can be formed by anaerobes and permits the denitrification of sewage effluents.
- What are biofilms?
- Biofilms are organized layers of microbial cells on surfaces.
- Give an example of a biofilm on a living surface.
- Examples of biofilms on a living surfaces are teeth, skin, and lungs.
- Give an example of a biofilm on a non-living surface.
- Examples of biofilms on non-living/inert surfaces are rocks, contact lenses, and prostheses.
- Why are biofilms important in medicine?
- Biofilms are important in medicine because control of biofilms on surfaces such as catheters, prostheses, contact lenses, and dialysis units is a constant issue. Also, biofilms can protect pathogens form disinfectants, create a focus for later occurrence of disease, or release micoroorganisms and microbial products that may affect the immunological system of a susceptible host.
- Why are biofilms important in the environment?
- Biofilms are important in the environment because biofilms have a profound impact on the development of ecosystems.