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Microbial Ecosystems - Freshwaters

10 important questions on Microbial Ecosystems - Freshwaters

What factors contribute to the significant variation in resources and conditions in freshwater environments?

Freshwater environments vary due to differences in isolation, pollution levels (from agricultural, industrial, or residential runoff), and the presence of oxygen-producing and oxygen-consuming organisms. The balance between photosynthesis and respiration controls natural cycles of oxygen, carbon, and other nutrients.

What are oxygenic phototrophs in aquatic environments, and how do they contribute to microbial communities?

Oxygenic phototrophs in aquatic environments include algae and cyanobacteria. They are primary producers and can be either planktonic or benthic. Their activity significantly influences chemoorganotrophic microbial communities by affecting primary production rates, organic matter production, and the development of anaerobic metabolisms.

Explain the influence of lake stratification on oxygen levels.

Lakes experience stratification, with warmer and less dense surface layers (epilimnion) separated from colder and denser bottom layers (hypolimnion). The thermocline is the transition zone between these layers. Stratification limits nutrient transfer between layers until fall turnover, impacting oxygen levels. Excessive organic matter production during high primary production rates can lead to bottom-water O2 depletion and anaerobic conditions.
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What is the annual turnover cycle in lakes, and how does it affect microbial activity and community composition?

The annual turnover cycle involves the transition of lake bottom waters from oxic to anoxic and back to oxic. Microbial activity and community composition are altered with changes in oxygen content. Factors like temperature and nutrient levels accompanying fall turnover govern microbial diversity and activity.

Define Biochemical Oxygen Demand (BOD) in freshwater systems, and how is it determined?

Biochemical Oxygen Demand (BOD) is the microbial oxygen-consuming capacity of a body of water. It is determined by taking a sample, saturating it with dissolved O2, incubating it in the dark for 5 days at 20°C, and measuring the residual oxygen. BOD provides a measure of the organic material in the water that can be oxidized by the microbes..

Explain the linkage between oxygen and carbon cycles in freshwaters.

In freshwaters, the levels of organic carbon and oxygen are inversely related. High Biochemical Oxygen Demand (BOD) leads to low dissolved oxygen levels. Anoxic aquatic environments result from respiratory processes that remove dissolved oxygen, leaving organic material to be mineralized by anaerobic metabolisms.

What are the major prokaryotic groups observed in lake surface samples, and which bacterial phyla are commonly found in freshwater lakes?

Major prokaryotic groups in lake surface samples include Proteobacteria, Actinobacteria, Bacteroidetes, Cyanobacteria, and Verrucomicrobia. Euryarchaeota, Crenarchaeota, and Thaumarchaeota are the major Archaea present. Proteobacteria dominate in both diversity and abundance, with Actinobacteria and Bacteroidetes also significant but in lesser abundance.

How do the major bacterial phyla in freshwater lakes compare to those in surface soils and the oceans?

he major bacterial phyla in freshwater lakes, including Proteobacteria and Bacteroidetes, share features with surface soils and the oceans. However, differences exist, such as the dominance of Alpha- and Betaproteobacteria in lakes, while Alpha- and Gammaproteobacteria predominate in the oceans. Betaproteobacteria respond quickly to periodic pulses of organic nutrients in lake systems.

What factors contribute to the high prokaryotic diversity observed in freshwater lakes?

High prokaryotic diversity in freshwater lakes results from seasonally variable inputs of endogenous and exogenous nutrients. Lakes sustain a phylogenetically and metabolically complex community of Bacteria and Archaea due to their dynamic character and nutrient fluctuations.

How do storms, floods, and droughts impact microbial productivity, diversity, distribution, and interactions in freshwater systems?

Storms, floods, and droughts are less predictable but significant factors determining the delivery, transport, and cycling of organic matter and inorganic nutrients in freshwater systems. They affect microbial productivity, diversity, distribution, and interactions, influencing the overall health and dynamics of freshwater ecosystems.

The question on the page originate from the summary of the following study material:

Brock Biology of Microorganisms, Global Edition | 9781292235103 | Michael T Madigan, et al

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