Chapter 4 - Dynamics of Microbial Growth

What is bacterial growth?

• An increase in bacterial cell numbers

How doe bacteria reproduce?

• Binary fission

What is the process of binary fission? (2)

• The bacterial cell elongates + makes a copy of its DNA

• Divides into 2 identical cells

What is the exponential growth of bacterial cells?

• The population of bacterial cells doubles every generation due to binary fission

What is generation time?

• The time required for a population to double

What is inoculation?

• Introducing microbes into a medium to start a culture

What is a culture? (1.2)

• Microbes growing in a medium

  • Batch

  • Continuous

What is a batch culture? (1.1)

• A closed system - no other nutrients added once started

  • Bacteria stops growing once the nutrients are used up

What is a continuous culture? (1.1)

• Open system - nutrients are continuously added, wastes are removed

  • Supports indefinite growth

What are the growth curve components in batch cultures? (5)

• Lag phase

• Exponential phase

• Stationary phase

• Death Phase

• Phase of prolonged decline

What is the lag phase?

• Period of adaptation - cells adjust to new media + get ready to grow

What is the exponential phase?

• Period of maximal production - used to calculate generation time

What is the stationary phase?

• Nutrients have been used up - wastes accumulate

What is the death phase?

• Toxic waste products have accumulated + cells die at a uniform rate

What is the phase of prolonged decline?

• A small fraction of population may survive the death phase - selects for strongest cells in the population

What are the temperature categories? (3)

• Minimum - lowest temp supporting growth

• Optimum - temp that supports best growth

• Maximum - highest temp supporting growth

What are psychrophiles? (1.1)

• Cold loving bacteria

  • Grows between 5-15^oC

What are psychrotrophs? (1.1)

• Cold tolerant bacteria

  • Optimum: 15-30C

What are mesophiles? (1.1.1)

• Moderate temp loving bacteria

  • Optimum temp: 25-45^oC

    • most pathogens optimum temp: 37^oC

What are thermophiles? (1.1)

• Heat loving bacteria

  • Optimum: 65^oC

What are hyperthermophiles?

• Bacteria that thrive in extreme environments - 75-121

What are obligate aerobes?

• Organisms that need O2 for respiration (energy generation)

What are facultative anaerobes?

• Organisms that can use O2, but can also grow in its absence

What are obligate anaerobes?

• Organisms that cannot use O2 - they’re killed by it

What are microaerophiles?

• Organisms that require O2 in low amounts - killed in high concentrations

What are aerotolerant anaerobes?

• Cannot use O2, but aren’t killed by it

What is pH?

• The measurement of acidity or alkalinity

What does it mean to be acidic?

• A pH below 7

What does it mean to be alkaline?

• A pH above 7

What does it mean to be neutral?

• A pH of 7

What are acidophiles?

• Bacteria that grows at a very low pH

What are alkaliphiles?

• Bacteria that grows at a high pH

What is osmosis? (1.1)

• The movement of solvent molecules → a semi-permeable barrier

  • H2O will move from area of high concentration → low concentration

What is a hypertonic solution? (1.1)

• High solute concentration

  • Water flows out of cell

What is a hypotonic solution? (1.1)

• Low solute concentration

  • Water flows → cell

What is plasmolysis?

• Cell drying up in a hypertonic solution

What is osmotic lysis?

• Cell bursts in hypotonic solution

What is an isotonic solution?

• Condition where solute concentration on outside of cell = inside cell

What are extreme halophiles?

• Microorganisms that thrive in environments with very high salt concentration

What are nutritional factors that influence growth? (6)

• Carbon

• Nitrogen, Sulfur, Phosphorous

• Trace elements

• Energy

What are heterotrophs?

• Organisms that take carbon from organic matter

What are autotrophs?

• Organisms that use inorganic carbon

Why is carbon important?

• Required for all organic molecules - backbone of living matter

Why is nitrogen, sulfur, and phosphorous important?

• Required in smaller amounts for the synthesis of cellular material

What are trace elements? (1.1)

• Elements required in very small amounts

  • Essential to the function of certain enzymes

Why is energy important?

• Organisms need energy to build cell material + drive cellular processes

What are chemotrophs? (1.1)

• Organisms that acquire energy from chemical compounds

  • may be inorganic or organic

What are phototrophs?

• Organisms that harvest energy from sunlight

What are photoautotrophs? (1.1)

• Organisms that use sunlight as energy and CO2 as a carbon source

  • Process called photosynthesis

What are photoheterotrophs?

• Organisms that use sunlight for every + obtain organic carbon from food

What are chemoautotrophs?

• Organisms that obtain energy from inorganic chemicals

  • Use CO2 as a carbon source 

What are chemoheterotrophs?

• Organisms that obtain energy from organic chemicals

  • Use the same organic chemicals as their source of carbon

What is solid media? (1.1.1)

• Agar Petri plates

  • made by adding sugar to liquid media

    • can’t be degraded by most bacteria

What are the benefits of solid media? (1.1)

• Allows growth of colonies

  • allows the isolation of pure cultures

What are colonies?

• A genetically identical population of cells

What does chemically defined mean?

• The exact chemical composition of the medium is known

  • also known as minimal media

What does chemically undefined mean?

• Media that contains rich organic ingredients - chemical composition is not known

  • e.g. complex media

What is selective media?

• Media that prevents the growth of unwanted organisms - allows only desired microbes to grow

What is differential media?

• Media used to distinguish different bacteria

  • All can grow - colonies of certain bacteria look different on the plate

What is the process of direct counting? (1.1.1)

• Cells are counted using a light microscope

  • Usually employs special counting chamber

    • inaccurate because it counts both dead + live cells

What is viable counting?

• Only live cells are counted

What is the process of viable counting? (1.1 + 1)

• A liquid culture is diluted + plated onto agar plates to grow colonies

  • Each colony on a plate represents a single cell from the original culture

• Colonies are counted + used to calculate the # of bacteria in the original culture

What are colony forming units?

• cfu per ml 

  • 1 cfu = 1 live bacterial cell