Module 5 - Environmental Microbiology Flashcards
What are the difficulties and limitations of growing microorganisms in the laboratory?
Growing microorganisms in the lab is challenging due to unknown environmental conditions (like pH, temperature, and salinity), unknown nutrient requirements, and the inability to cultivate most microorganisms using traditional methods. Culture-dependent methods cannot replicate environmental conditions, and cultured microorganisms are often only minor components of the microbial ecosystem.
How many microbial cells are estimated to exist on Earth, and why is this significant?
Approximately 5 × 10³⁰ microbial cells are estimated to exist, with most found in oceanic and terrestrial subsurfaces. This highlights the vastness of microbial diversity, indicating that microorganisms play critical roles in ecosystems worldwide.
Why is the 16S rRNA gene important in microbial diversity studies?
The 16S rRNA gene is widely used as a marker for phylogenetic analysis due to its conserved nature and presence in all prokaryotes. It serves as a reliable tool for determining evolutionary relationships and exploring microbial diversity in various environments.
What are some key divisions (phyla) of bacteria and archaea?
Important bacterial divisions include Proteobacteria, Firmicutes, Actinobacteria, and Cyanobacteria, among others. For Archaea, key phyla are Euryarchaeota and Crenarchaeota. Many groups are defined primarily from environmental sequences without any cultured representatives, emphasizing the limitations of culture-dependent methods.
How do temperature, pH, salinity, and pressure affect microbial growth?
Temperature: Psychrophiles thrive in cold temperatures (<15°C), thermophiles grow optimally between 45-80°C, and hyperthermophiles thrive above 80°C.
pH: Acidophiles prefer low pH environments (<6), alkaliphiles thrive in high pH (>8), and neutrophiles grow best in neutral conditions (pH 6-8).
Salinity: Halophiles thrive at moderate salinity (1-15% NaCl), while extreme halophiles require higher concentrations (15-30% NaCl) for optimal growth.
Pressure: Barophiles thrive under high pressure; barotolerant organisms can survive high pressure but also exist in less extreme environments.
What is the ‘Great Plate Count Anomaly’?
This anomaly refers to the observation that viable plate count techniques underestimate microbial diversity, revealing that less than 1% of environmental microorganisms can be cultivated in the lab.
What methods are used to measure microbial diversity without culturing?
Culture-independent methods, such as DNA sequencing (especially the 16S rRNA gene), allow researchers to measure microbial diversity and determine evolutionary relationships without the need for cultivation.
How do microorganisms adapt their membranes to survive extreme environments such as cold, heat, and high pressure?
Psychrophiles have higher amounts of unsaturated fatty acids in their membranes, which keeps them semi-fluid at low temperatures.
Thermophiles possess lipids rich in saturated fatty acids (Bacteria) or a lipid monolayer (Archaea), stabilizing their membranes at high temperatures.
Barophiles have a higher proportion of unsaturated fatty acids, preventing membrane gelling under high pressure.
What is a facultative anaerobe?
A facultative anaerobe is an organism that can grow in both the presence and absence of oxygen. It typically grows better in the presence of oxygen but can switch to fermentation or anaerobic respiration when oxygen is not available.
Why is O₂ used preferentially as an electron acceptor over NO₃⁻?
O₂ is preferred because it has a higher reduction potential, allowing for more efficient energy release during oxidation-reduction (redox) reactions. This results in a greater yield of ATP compared to using nitrate (NO₃⁻) as an electron acceptor.
What are the names of the two phosphorylation processes for forming ATP?
The two phosphorylation processes are:
1. Substrate-level phosphorylation: ATP is directly synthesized from an energy-rich intermediate during metabolic reactions.
2. Oxidative phosphorylation: ATP is generated through the proton motive force created by the electron transport chain, primarily during aerobic respiration.
Why is understanding microbial growth in relation to oxygen important?
Understanding microbial growth in relation to oxygen is crucial as it impacts the metabolic pathways used by microorganisms. Aerobes require oxygen for growth, while anaerobes do not and can even be killed by oxygen. The ability to adapt to different oxygen levels allows microbes to occupy various ecological niches.
What is the significance of microbial metabolic diversity?
Microbial metabolic diversity allows organisms to utilize a range of substrates and energy sources, making them adaptable to various environments. This diversity is vital for ecological functions such as decomposition, nutrient cycling, and the maintenance of ecosystem stability.
Why are oxidation-reduction (redox) reactions critical in microbial metabolism?
Redox reactions are fundamental for the conservation and transfer of energy within microbial cells. They involve the transfer of electrons from electron donors to electron acceptors, which is essential for processes like ATP synthesis and the metabolism of organic and inorganic compounds.
How do aerobic respiratory pathways benefit bacteria and archaea?
Aerobic respiratory pathways allow bacteria and archaea to utilize O₂ as the terminal electron acceptor, leading to the efficient production of ATP through oxidative phosphorylation. This process generates more energy compared to anaerobic processes, which is crucial for energy-demanding cellular activities.
What is the role of electron carriers in respiration?
Electron carriers, such as NAD⁺ and FAD, shuttle electrons during redox reactions, facilitating the transfer of energy within the cell. They help in maintaining the flow of electrons through the electron transport chain, which is vital for ATP production.
