chapter 3-4

Phototrophy

  • Light Reaction

    • Utilizes light to generate proton motive force and reducing power.

    • ATP synthase produces ATP through photophosphorylation.

    • Can be:

      • Oxygenic Phototrophy: Produces O2 as a waste product (e.g., cyanobacteria, algae, plants).

      • Anoxygenic Phototrophy: Does not produce O2 (common in many bacteria).

The Calvin Cycle

  • Light Reaction:

    • Converts light energy into ATP and NADPH, facilitating the Calvin Cycle (dark reaction) for carbon fixation.

    • in chloroplast

      1. carbon fixation

      2. reducing power

      3. regeneration of RuBP

4.1 Feeding the Microbe: Cell Nutrition

  • Macronutrients

    • Nutrients required in large amounts:

      • Carbon (C), Oxygen (O), Nitrogen (N), Hydrogen (H), Phosphorus (P), Sulfur (S), Potassium (K), Sodium (Na), Calcium (Ca), Magnesium (Mg), Chlorine (Cl), Iron (Fe).

      • proteins = most abundant

  • Micronutrients

    • Required in small amounts; include trace metals and growth factors.

      • trace metals: iron (O2 transfer, cellular respiration, etc.) copper, zinc, and manganese

      • growth factors: amino acids, vitamins, hormones

        • cyanobacteria make own growth factors.

4.2 Growth Media and Laboratory Culture

  • Classes of Culture Media

    • Defined Media: Exact chemical composition is known. e.g minimal salt media

    • Complex Media: Composed of digests from microbial, animal, or plant sources (e.g., yeast, meat extracts). exact composition unknown. e.g. butrient broth

    • Selective Medium: Contains compounds that selectively inhibit the growth of certain microbes while allowing others to grow. e.g MAC agar inhibits growth of gram-positive bacteria

    • Differential Medium: Contains indicators (often dyes) that reveal particular metabolic reactions during microbial growth. e.g. blood agar differentiates between hemolytic and non-hemolytic

  • Types of Culture Media

    • Available as liquid or solid (solidified by adding agar).

    • Typically sterilized in an autoclave.

Counting Cells

  • Methods:

    • Optical Density: Measurement of light absorbance.

      • convenient, not direct

    • Direct Count:

      • Microscopic Count: Enumerates cells present by observation.

      • Viable Count: Counts only living cells and assume each colony came from single cell

        • more direct

        • diluting sample = CFU = estimation of density of viable organisms

Counting Cells Calculation Example

  • Volume of counting chamber = 0.1 µl.

  • Jane's experiment with 10 µl sample, diluted:

    • Total cells = 100 in 5 shaded squares.

    • Cells in 0.1 µl = 500.

    • Cells in 1 µl = 5000.

    • Cells in 1 ml = 5 x 10^6 (considering dilution factor of 10).

    • Final assessment: 5 x 10^7 cells in 1 ml of broth culture.

Microbial Growth Curve

  • Typical Growth Curve:

    • lag phase:

      • cells adjust to new environmental conditions.

      • length depends on previous growth conditions

      • longer lag when moving fro nutrient rich → nutrient poor

    • Exponential (log):

      • cells double at regular intervals

      • growth = balanced = ideal phase for experiments

      • rate varies depending on species, medium, env. factors.

    • stationary:

      • growth slows because of nutrient depletion/toxic waste accumulation

      • no net increase or decrease in cell number

      • cells shift metabolism towards maintenance and survival

    • death phase:

      • due to resource exhaustion

      • cell death increases, more than viable cell count

Quiz Section

  • Quiz 1-31 Overview

    • Questions:

      • Enzymes lower activation energy, increasing reaction rate.

      • True or False: Fermentation is a form of anaerobic respiration.

      • During the death phase, microscopy count is often higher/lower/similar to viable count (depends on context).

Growth Rate Dynamics

  • Exponential Growth Characteristics:

    • Constant generation time (g) for population to double

    • formula: t/n, where N is cell number at time t, N0 is initial cell number.

    • consequence: small initial populations can grow exponentially in short amount of time = competition and food spoilage

Continuous Culture

  • Described as an open system for maintaining microbial cultures.

  • e.g. Chemostat: A device that allows for the continuous flow of nutrients and the removal of waste products, thereby stabilizing the growth of microorganisms (maintain exponential growth)

  • batch culture: closed system, limited growth

Biofilm Growth

  • Growth Types:

    • Planktonic Growth: Free-floating cells in suspension.

    • Sessile Growth: more advantageous

    • Attached to surfaces, capable of forming biofilms.

    • Biofilms exhibit properties distinct from planktonic cells; significant in medical (cavities, chronic infections) and industrial contexts (contaminate, cause plugging, reduce ship efficiency).

    • microbial mats: structured communities of microorganisms that can form on surfaces, often composed of multiple layers of different species, found in extreme environments

    • promote intercellular communication and protection

    • can have drug resistance because of penetration barriers. e.g. pseudomonas aeruginosa: a common biofilm-forming bacterium known for its ability to develop resistance to multiple antibiotics, making it a significant concern in chronic infections and healthcare settings.