CH. 21 & 22 Microbial Ecology Flashcards
What is the hydrologic cycle and what are the components that drive this?
The cyclic exchange of water between the atmosphere and biosphere
Water precipitates as rain -> fall to Earth -> water pass through the ground and picked up nutrients causing carbon runoff to accelerate and oxygen to deplete -> returned by evaporation to the air
How does microbial activity affect the hydrologic cycle? What is BOD and what do high/low BOD values indicate? How is BOD measured?
Microbial oxygen consumption creates a biochemical oxygen demand (BOD)
BOD is the amount of oxygen removed from the environment by aerobic respiration
High BOD threatens the viability of fish and other aquatic animals when oxygen levels are less than 5mg/L. Low BOD indicates less oxygen is being removed = water is purer
What are zones of hypoxia? What is their significance? How do these occur?
Large regions of the ocean with low oxygen that lack most fishes and invertebrates (also known as dead zones)
Its significance is that heterotrophs increase in their response to the influx of organic nutrients, yet, aerobic respiration from the heterotrophs depletes oxygen leading to a high number of the aquatic animals death and the increase of heterotrophic bacteria feeding on the dead organisms
What is eutrophication? How does this occur?
The excessive richness of nutrients (NH4, NO3, PO4, etc.) in a lake or other body of water (frequently due to runoff from the land) causes a dense growth of plant life and death of animal life from lack of oxygen
What is the purpose of wastewater treatment? Describe the stages of wastewater treatment typically found at a treatment plant.
It is to decrease the BOD and the level of human pathogens before water is returned to local rivers
Stages:
-Preliminary treatment (removes solid debris)
-Primary treatment (fine screens & sedimentation tanks remove insoluble particles)
-Secondary treatment (microbial decomposition of organic content by activated sludge)
-Tertiary treatment (chlorination or other chemical applications to eliminate pathogens)
What is activated sludge? How do methanogens contribute to wastewater treatment?
A process for removing/treating wastewater using air and a biological floc composed of bacteria and protozoa
Methanogens contribute to wastewater treatment by breaking down organic acids efficiently
Why is the presence of filamentous bacteria important?
Filamentous bacteria are the base of the structure to which other bacteria can attach/settle and form flocs (flocculation) to prepare the solids for subsequent removal. They help create the optimal ratio of filamentous to planktonic types
What are saprophytes?
-Microorganisms that feed on the decayed matter
-Composed of amoebae, ciliated protozoans, stalked ciliates, etc.
-Has an important protozoan flora
What are the different forms of nitrogen present in the global nitrogen cycle?
-Organic nitrogen
-Ammonium (NH4)
-Nitrite (NO2),
-Nitrate (NO3)
-Nitrous oxide ( N2O)
-Nitric oxide (NO)
What is the “nitrogen triangle”? What are the processes that comprise the three parts of the triangle?
Atmospheric N2 —(Fixation)—> Reduced Nitrogen (NH3, NH4)
Reduced Nitrogen —(Nitrification)—> Oxidized Nitrogen (NO2, NO3)
Oxidized Nitrogen —(Denitrification)—> cycle starts again with N2
Describe: nitrogen fixation; nitrification, and denitrification. Which processes are lithotrophic? Which is anaerobic
respiration?
Nitrogen fixation: the processes by which atmospheric nitrogen is fixated into ammonia, to ammonium, then assimilated into organic compounds, especially by certain microorganisms
Nitrification: Free ammonia in soil or water is quickly oxidized for energy by nitrifiers, bacterial species that possess enzymes for oxidation of ammonia to nitrite (NO2), or of nitrite to nitrate (NO3). (lithotrophic)
Denitrification: The reduction of nitrate/nitrite into atmospheric nitrogen form by a series of reduction (anaerobic respiration)
What is the difference between assimilatory & dissimilatory nitrate reduction, respectively?
Assimilatory: The uptake of nitrate and reduction to NH4+ for fixation into biomass
Dissimilatory: Energy-yielding metabolism in which nitrate (NO3–) is reduced to nitrite (NO2–), diatomic nitrogen (N2), and in some cases ammonia (NH3). Also known as DENITRIFICATION
Describe symbiotic relationship between nitrogen fixation rhizobia and certain plants.
-Rhizobia fix more nitrogen than the plants absorb from the soil
-Rhizobia move to the plant root to promote root curling by releasing the Nod factor
-Rhizobia form nodules on the plant root, within which the bacteria can convert atmospheric nitrogen into ammonia that can be used by the plant
How do hypoxic zones relate to denitrification and production of the greenhouse gas N2O?
The greenhouse (N2O) is associated with the usage of nitrogenous fertilizers which are oxidized nitrogen pollutants. Denifitrication is also related because N2O is reduced to NH4 which is then oxidized into NO2/NO3 in aquatic environments causing hypoxic zones
What is the anammox reaction? What is its significance?
A reaction carried out by bacteria and archaea that oxidizes ammonium to dinitrogen gas using nitrite as the electron acceptor
It is significant in accounting for a majority of all nitrogen returned to the atmosphere
