Lecture 7 Flashcards
microbial growth and nutrition (19 cards)
Describe the roles of carbon, hydrogen, oxygen, nitrogen, trace elements, and vitamins in microbial growth and reproduction.
Carbon: Essential for organic molecules (proteins, lipids, carbohydrates, nucleic acids).
Hydrogen: Found in water and organic compounds; involved in energy production.
Oxygen: Used in aerobic respiration; component of water and organic molecules.
Nitrogen: Needed for proteins, nucleic acids, and ATP.
Trace elements (iron, zinc, copper): Required in small amounts for enzyme function.
Vitamins: Serve as enzyme cofactors and growth factors.
Compare four basic categories of organisms based on their carbon and energy sources.
Photoautotrophs: Use light for energy and CO₂ for carbon (cyanobacteria).
Chemoautotrophs: Use inorganic chemicals for energy and CO₂ for carbon (nitrifying bacteria).
Photoheterotrophs: Use light for energy but organic compounds for carbon (e.g., purple non-sulfur bacteria).
Chemoheterotrophs: Use organic compounds for both energy and carbon (most bacteria, fungi, and animals).
Distinguish among anaerobes, aerobes, aerotolerant anaerobes, facultative anaerobes, and microaerophiles.
Aerobes: Require oxygen.
Anaerobes: Cannot tolerate oxygen.
Facultative anaerobes: Prefer oxygen but can grow without it.
Aerotolerant anaerobes: Do not use oxygen but tolerate it.
Microaerophiles: Require low oxygen levels.
Explain how oxygen can be fatal to organisms by discussing singlet oxygen, superoxide radical, peroxide anion, and hydroxyl radical; describe how organisms protect themselves from toxic forms of oxygen.
Singlet oxygen (¹O₂): High-energy form, neutralized by pigments like carotenoids.
Superoxide radical (O₂⁻): Toxic byproduct of respiration; removed by superoxide dismutase (SOD).
Peroxide anion (O₂²⁻): Found in hydrogen peroxide; broken down by catalase or peroxidase.
Hydroxyl radical (OH·): Extremely reactive; antioxidants help neutralize it
Define nitrogen fixation, and explain its importance.
Definition: Conversion of atmospheric nitrogen (N₂) into ammonia (NH₃) by bacteria (Rhizobium).
Importance: Provides usable nitrogen for plants and other organisms.
Explain how extremes of temperature, pH, and osmotic and hydrostatic pressure limit microbial growth.
Temperature: Too high denatures proteins; too low slows metabolism.
pH: Acidic or alkaline conditions can disrupt enzyme function.
Osmotic pressure: High salt/sugar concentrations draw water out of cells.
Hydrostatic pressure: High pressure affects membrane integrity
Describe how quorum sensing can lead to formation of a biofilm.
Quorum sensing: Microbes release and detect signaling molecules to coordinate behavior.
Biofilm formation: Quorum sensing triggers adhesion and protective extracellular matrix production
Describe the two most common methods by which microorganisms can be isolated for culture.
Streak plate method: Spreading bacteria across an agar surface to obtain individual colonies.
Pour plate method: Diluting a sample in liquid agar and pouring it into plates.
Describe six types of general culture media available for bacterial culture.
Defined media: Exact chemical composition is known.
Complex media: Contains unknown compositions (nutrient agar).
Selective media: Encourages growth of some microbes while inhibiting others.
Differential media: Distinguishes between microbes (blood agar).
Anaerobic media: Supports growth of anaerobes (reducing media).
Transport media: Preserves specimens for transport
Describe enrichment culture as a means of enhancing the growth of less abundant microbes.
Uses specific conditions to favor the growth of rare microbes over others.
Discuss the use of animal and cell culture and low-oxygen culture.
Animal cultures: Used for viruses and certain pathogens.
Cell cultures: Grow viruses and intracellular bacteria.
Low-oxygen cultures: Grow microaerophiles and anaerobes.
Contrast refrigeration, deep-freezing, and lyophilization as methods for preserving cultures of microbes.
Refrigeration (4°C): Short-term storage.
Deep-freezing (-80°C or lower): Long-term storage.
Lyophilization (freeze-drying): Removes water for very long-term storage.
Describe binary fission as a means of reproduction.
Asexual reproduction where a single cell divides into two identical daughter cells.
Explain what is meant by the generation time of bacteria
Time required for a population to double - E. coli ~20 mins
Describe logarithmic growth.
Exponential increase in bacterial population
Draw and label a bacterial growth curve.
Phases: Lag, Log (Exponential), Stationary, Death
Describe what occurs at each phase of a population’s growth
Lag phase: Adaptation, little growth.
Log phase: Rapid, exponential growth.
Stationary phase: Growth slows due to resource depletion.
Death phase: Cells die faster than they reproduce.
Explain how a chemostat can maintain a microbial culture in a continuous phase.
Continuously adds nutrients and removes waste to maintain growth phase.
Contrast direct and indirect methods of measuring bacterial reproduction.
Direct: Counting under a microscope, plate counts, flow cytometry.
Indirect: Measuring turbidity (cloudiness), metabolic activity, dry weight.
