Envrionmental Microbiology

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Questions and Answers

What is transported from heterocysts to vegetative cells?

Reduced nitrogen (correct)

Oxygen molecules

Carbon dioxide

Sugars

What role do sugars play in the interaction between vegetative cells and heterocysts?

They attract heterotrophic bacteria. (correct)

They are converted into nitrogen compounds.

They inhibit the growth of vegetative cells.

They are only produced in heterocysts.

What process is inhibited by the presence of heterotrophic bacteria around heterocysts?

Sugar production

Photosynthesis activity

Oxygen transport

Nitrogen fixation (correct)

What determines the spacing of heterocysts in a filament?

The diffusion of sugars and organic nitrogen compounds Signup and view all the answers

Why do heterocysts become anaerobic?

Because of colonization by heterotrophic bacteria Signup and view all the answers

What is the primary reason microbial indicators are useful in environmental monitoring?

Microbes have rapid growth rates and specific physiological responses Signup and view all the answers

Which of the following is NOT considered a characteristic of bioindicators?

They are always species-specific Signup and view all the answers

What is an example of a microbial process that can serve as an indicator of environmental health?

Respiration measured by biological oxygen demand (BOD) Signup and view all the answers

Which of the following best explains the concept of microbial symbiosis?

Microbes can form beneficial relationships with plants and animals, optimizing their growth Signup and view all the answers

What is a common method for assessing the presence of microbial indicators?

Using direct colony-forming unit (cfu) counts and biomarker molecules Signup and view all the answers

How do microbial communities contribute to biogeochemical cycling?

They mediate the transformation and recycling of nutrients and organic matter Signup and view all the answers

What type of organisms can be considered as bioindicators?

Any organisms displaying sensitivity to environmental changes, including microbes Signup and view all the answers

Which of the following statements about canaries in coal mines is accurate?

Canaries serve as bioindicators of toxic gases in mines Signup and view all the answers

What is the role of microbial photosynthesis in the ecosystem?

It reduces carbon dioxide into organic carbon and produces oxygen. Signup and view all the answers

Which of the following statements about hopanoids is true?

They are found in the cell membranes of phototrophs. Signup and view all the answers

Which statement best describes the biogeochemical cycles in relation to microbes?

Microbes drive these cycles by participating in redox reactions. Signup and view all the answers

What does CO2 fixation primarily involve?

The production of organic carbon compounds from CO2. Signup and view all the answers

Which of the following organisms are responsible for oxygenic photosynthesis?

Photoautotrophs and cyanobacteria. Signup and view all the answers

What characteristic makes hopanoids useful as biomarkers?

They are stable and resistant to degradation. Signup and view all the answers

What does the accumulation of oxygen in the atmosphere allow for?

The development of humans and multicellular life. Signup and view all the answers

Which of the following elements are considered essential in biogeochemical cycles?

Oxygen, hydrogen, sulfur, and phosphorus. Signup and view all the answers

What is one function of hopanoids in microbial cells?

They help in the localization of proteins within the membrane. Signup and view all the answers

Which mode of genetic inheritance is common among microbes?

Horizontal gene transfer through various mechanisms. Signup and view all the answers

What is the primary function of mycorrhizae in plants?

Nutrient exchange Signup and view all the answers

How do fungi contribute to phosphate availability in soil?

By lowering the pH of soil Signup and view all the answers

Which enzyme types are adapted to different pH conditions in fungi and bacteria?

Phosphatases Signup and view all the answers

Which type of mycorrhiza forms inside plant roots?

Arbuscular mycorrhizae Signup and view all the answers

What environmental condition favors fungal growth over bacteria?

Acidic pH Signup and view all the answers

What is the common form of phosphorus that microbes predominantly uptake in soils?

PO4+2 Signup and view all the answers

Which of the following statements is accurate about mycorrhizae's prevalence?

Found on 95% of examined plants Signup and view all the answers

What role do mycorrhizae play in the ecological niche they create?

They create a low pH environment Signup and view all the answers

Which statement accurately describes the relationship between energy and carbon sources?

Energy from light, carbon from CO2; energy from oxidation of inorganic compounds, carbon from organic sources. Signup and view all the answers

Which reduction process in the sulfur cycle is more common and better controlled within a cell?

Reduction of SO4-2 to SO3-2. Signup and view all the answers

What is the primary function of the enzyme nitrogenase?

Reduction of N2 to NH3. Signup and view all the answers

Which type of cell do cyanobacteria specifically use for nitrogen fixation?

Heterocysts. Signup and view all the answers

During the oxidation of sulfur compounds, which sequence represents the decreasing order of oxidation state?

SO4-2 > SO3-2 > SO2 > S > H2S. Signup and view all the answers

Which of the following combinations of energy and carbon sources reflects an incorrect pairing?

Energy from light, carbon only from CO2. Signup and view all the answers

In the context of cellular respiration, which energy source is least likely to be utilized by organisms?

Energy solely from CO2. Signup and view all the answers

What distinguishes the reduction of SO4-2 to SO3-2 from that of SO4-2 to H2S?

SO4-2 to SO3-2 is more common and tightly controlled. Signup and view all the answers

What role does the pentapeptide play in the intracellular environment of heterocysts?

It facilitates the degradation of HetR. Signup and view all the answers

How is HetR affected by starvation signals in heterocysts?

It accumulates in response to chemical signals. Signup and view all the answers

What is indicated by a thick cell wall in the context of heterocysts?

Resistance to environmental stress. Signup and view all the answers

What happens to HetR once it is made in heterocysts?

It is immediately degraded by pentapeptides. Signup and view all the answers

What type of cellular activity does HetR primarily involved in?

Regulation of metabolic processes. Signup and view all the answers

Which of the following describes the effect of pentapeptides on HetR?

They degrade it once synthesized. Signup and view all the answers

What does the degradation of HetR signify for the heterocyst’s function?

Maintenance of cellular homeostasis. Signup and view all the answers

During starvation, how does the presence of pentapeptides influence the cell?

They signal increased degradation of proteins. Signup and view all the answers

What is the likely consequence of HetR misfolding within a cell?

Loss of protein function. Signup and view all the answers

How do the starvation signals diffuse in the context of heterocysts?

From neighboring heterocysts to the wider environment. Signup and view all the answers

Study Notes

Readings

Chapter 19 covers microbial system measurement (useful for tutorial presentations), including molecular approaches. Week 5 lecture examines microbial ecology basics.
Chapter 20 details microbial ecosystems (Week 6 Environmental Microbiology lecture).
Chapter 21 discusses nutrient cycles (Week 6 Environmental Microbiology lecture).
Chapter 23 explores microbial symbioses with microbes, plants, and animals (Lecture 7, Week 8, Microbial interactions).

Indicator Species

Indicator species are biological processes, species, or communities. Changes in their size reflect changes in environmental parameters.
Often anthropogenic, but can also be natural.
Indicator species demonstrate clear physiological responses to environmental variables. Examples include canaries in coal mines, frog spawn and pollution indicators.

Fitness / Abundance/ Environmental Gradient

A. Bioindicators: Fitness/abundance is high in middle of environmental gradient.
B. Rare species: Very high fitness/abundance at one particular point in the gradient.
C. Ubiquitous species: Fitness/abundance is uniformly moderate throughout the gradient.

Microbial Indicators

Microbes are indicators of biological processes, including:
- Primary Productivity
- Respiration (BOD)
- Biogeochemistry
Microbes are used as indicator species, either directly (CFU counts) or indirectly (biomarker molecules).
Biomarkers include diagnostic molecules (e.g., fatty acid, DNA, protein) identifying organisms.

Microbial Systems and Ecology

Microbial systems are amenable to ecology due to:
- Large population sizes
- Short generation times
- Genetic manipulation capabilities
- Readily accessible for sampling
- Experimentally tractable nature
- Different modes of genetic inheritance

Life on Earth

Ecosystems are environmental units where abiotic (physical) components interact with biotic (organism) communities.
Microbial photosynthesis produces organic carbon from CO2 and oxygen as a byproduct.
Primary productivity assesses the rate of CO2 reduction into organic carbon compounds from CO2.
Chemoautotrophs and photoautotrophs perform this process.
Oxygenation of Earth's atmosphere allowed organisms to respire organic carbon with oxygen to produce carbon dioxide.

Oxygenic Photosynthesis Made Earth Habitable

Chart demonstrating historic changes in atmospheric oxygen and carbon dioxide levels throughout Earth’s history, relating to oxygenic photosynthesis.

Microbial Fossils

Images of microbial fossils.

Hopanoids-Molecular Fossils

Hopanoids are characteristic biochemical structures. Diagenesis converts hopanoids into sedimentary hopanoids.
Specific hopanoids are characteristic of phototrophs (2-methylhopanes)
These data can be used to date photosynthesis before oxygenation of the atmosphere.

Hopanoids

Lipids found in cell membranes, playing a role in membrane fluidity, stress, and protein localization.
Highly stable biomarkers, unlike DNA/RNA/proteins.
2-methylhopanoids and cyanobacteria are linked.
Hopanoids date the occurrence of oxygenic photosynthesis.

Life on Earth(Biogeochemical Cycles)

Microbes drive biogeochemical cycles crucial for life.
Cycles allow essential elements to be reused through various habitats and spheres.
Examples include:
- Nitrogen
- Phosphorus
- Carbon
- Oxygen
- Hydrogen
- Sulfur

Oxidizing/Reducing Strength

Table illustrating oxidizing/reducing strength of various elements.

The Sulfur Cycle

S04-2 --> SO3-2 --> SO2 --> S2O3-2--> S --> H2S

Sulfur exists in multiple oxidation states.

Sulfate Reduction

Sulfate-reducing bacteria have short electron transport chains (ETC), as energy available is less than oxygen.
Sulfidogens are microbes that produce H2S.
These organisms are usually obligate anaerobes in soil and marine environments.

From Sulfate Reducers to Sulfidogens

Process diagram depicting the conversion of sulfate to sulfide
protons pumped outside to create electron potential
energy generated from all è moves inside to handle

Sulfur Oxidation (Chemoautotrophs)

ETC (electron transport chain) can be reversed in sulfur oxidizers because H2S, and S2O32- are weaker electron donors than NAD+/NADH.
Electrons from these fuel sources are fed to the ETC and are equivalent to their Eo.
Proton motive force is formed at quinone (Q) and terminal oxidase (cytochrome - cyt).

The Nitrogen Cycle

NO3- --> NO2- --> NO --> N2O --> N2 --> NH3 --> NH4+

Shows conversion of nitrogen into various forms.
Processes include:
- Denitrification (CH3OH): N2 production
- Anammox: conversion of ammonia and nitrite to N2
- Nitrification: ammonia to nitrite, to nitrate.

Nitrogen Fixation

Reduction of dinitrogen gas to ammonia by enzyme nitrogenase (O2 sensitive).
Essential for life, as nitrogen is converted into biologically available forms.
Energy intensive, requiring a two-enzyme complex (dinitrogenase and dinitrogenase reductase). It is an anaerobic process.
Only prokaryotes conduct nitrogen fixation. Symbiotic bacteria associated with plants (e.g., Rhizobia) & certain free-living species (e.g., Cyanobacteria, Azotobacter, Clostridium) are examples. Nitrogen fixation is a major limitative factor for life cycles.

Soil Community & Cultured Microbe

Microbes in soil convert N2 to NH4+.
Look at genes involved in the pathway.

Mycorrhizae (Symbiotic Associations)

Symbiotic systems between plant roots and fungi.
Found in 95% of examined land plants.
Symbiosis for nutritional exchange. Types:
- VAM (arbuscular mycorrhizae): Inside plant root
- Ectomycorrhizae: Outside plant root.
Fungi dissolve mineral compounds like phosphorus, sulfur, iron.
They exchange phosphate from soil for sugars produced by plants through photosynthesis. This is essential in phosphate-limited systems.

Heterocysts

Specialised cells in cyanobacteria that fix nitrogen.
Thickened cell walls reduce oxygen permeability.
Absence of chlorophyll avoids oxygen generation.
Reduced nitrogen is transported to other vegetative cells for use.
Sugar transport from vegetative cells to heterocysts, attracting heterotrophic bacteria that consume both oxygen and sugars.
The diffusion of these compounds affects heterocyst spacing.

Mycorrhizae Benefits

Improved transplant survival/growth/rooting
Improved soil structure
Increased fertilizer utilization
Decreased drought tolerance
Reduction of off-site pollution
Disease reduction

Mycorrhizae in Succession

Key role in developing soils.
Exported exo-enzymes make micronutrients available to the biosphere
Modifies soil/habitat characteristics.
This impacts the ability of other plant species to colonise the area over time.

Possible Mechanisms of Reduction of Infection by Pathogens

Antifungal actions via antibiotic production, chemical barriers, chemical exudates, and defensive microbial populations (protecting from pathogens).

Relationships Between Phylotype Diversity and Environmental Factors

Correlation analysis between phylotype diversity and factors like mean annual temperature (MAT), latitude, potential evapotranspiration (PET), and soil pH levels.

Past Exam Questions

Series of multiple-choice questions focused on topics such as the use of 2-methylhopanoids as biomarkers, photosynthetic processes, energy and carbon sources for different microbial types, elements in the sulfur cycle, reduction of SO4-2 to H2S, nitrogenase and its role in nitrogen fixation, the type of cells used for nitrogen fixation in cyanobacteria, different microbial functional types etc.

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Description

Explore the fascinating relationship between heterocysts and vegetative cells in cyanobacteria. This quiz covers crucial aspects such as transportation of substances, roles of sugars, inhibition processes by heterotrophic bacteria, and factors influencing heterocyst spacing and anaerobic conditions. Test your understanding of these vital biological interactions!