Lesson 6 - Microbial Growth

Why are microorganisms studied in pure cultures, and why are most difficult to culture?

• Microorganisms naturally exist in complex, multispecies communities.

• Pure cultures allow scientists to study one microbial species independently.

• Fewer than 1% of microorganisms are culturable in pure culture.

• Many require specific nutrients, environmental conditions, or interactions with other organisms.

How do we measure growth and what is the importance of understanding nutrient requirements?

• We measure growth under the optimal nutritional and environmental conditions

• Assumes understanding of the growth requirements (nutritional, energy, physical, chemical)

• Importance of understanding nutrient requirements;

  • Characterization of microbes

  • Increased understanding of beneficial / undesirable microbial impacts: e.g., Plant and animal health & disease, ecosystems, agriculture, etc.

  • Optimized usage of beneficial microbes: e.g., microbial production of pharmaceuticals, enzymes, recombinant proteins, value-added compounds, food production processors, etc

Why are many prokaryotes (99%) unable to grow independently in laboratory cultures?

• Some species have adapted so well to their natural habitats that we still do not know how to grow them in the lab

• Some depend on essential factors supplied by other microorganisms in their ecological niche.

• Intracellular parasites require living host cells.

• Obligate symbionts depend on their partners for survival or growth. Many are considered unculturable because their specific growth requirements remain unknown.

Why do microorganisms have different nutritional requirements?

• Microorganisms evolved to inhabit different ecological niches.

• Different environments provide different nutrients and growth conditions.

• Therefore, microbial species have different nutritional requirements based on their physiology and adaptations.

What is the difference between macronutrients and micronutrients in microbial growth?

• Both: Essential nutrients (macro and micro) are those that must be supplied from the environment

• Macronutrients:

  • Required in relatively large amounts.

  • Used to construct cellular molecules and support cellular functions.

  • Examples: C, H, O, N, P, S, Mg, K, Ca.

• Micronutrients:

  • Required in relatively small amounts.

  • Often function as enzyme cofactors.

  • Examples: Co, Cu, Mn, Mo, Ni, Zn.

What is the difference between nutrition and nutrients?

• Nutrition: The process by which chemical substances (nutrients) are acquired from the environment and used for cellular activities.

• Nutrients: Substances obtained from the environment and used for catabolism and anabolism.

What is the difference between catabolism and anabolism?

• Metabolism = Catabolism + Anabolism

• The energy needed to build cells comes from chemical reactions

• Catabolism:

  • Breaks larger molecules into smaller molecules.

  • Exergonic reactions that release energy.

• Anabolism:

  • Builds larger molecules from smaller molecules.

  • Endergonic reactions that require energy.

• Catabolism provides energy for anabolism.

What three factors are used to classify microorganisms based on their nutritional requirements?

• Like all living things, microbes need sources of carbon and energy to grow

• Carbon source: Where the organism obtains carbon to construct cellular components (what am I made of?)

• Energy source: Whether energy comes from light or chemical reactions.

• Electron donor: The substance that gives up electrons during metabolic reactions (Power)

What is the difference between autotrophs and heterotrophs?

• How Microbes Build Biomass…All of Earth’s lifeforms are built on carbon which they acquire in different ways!

• Autotrophs:

  • Obtain carbon from inorganic sources (CO₂). (Sun is not the source, can only help fix the carbon)

  • Fix CO₂ into organic carbon molecules (mainly sugars).

  • Examples: Plants, algae, autotrophic bacteria.

• Heterotrophs:

  • Obtain carbon from preformed organic molecules.

  • Examples: Animals and many bacteria.

• This classification describes carbon source, NOT energy source.

What is the difference between phototrophs and chemotrophs?

• Phototrophs:

  • Capture light energy to support cellular activities.

• Chemotrophs:

  • Obtain energy from chemical reactions.

• This classification describes ENERGY source, not carbon source.

What is the difference between organotrophs and lithotrophs?

• Organotrophs:

  • Use organic compounds as electron/hydrogen donors.

  • Often heterotrophic - using organic compounds as sources of both electrons and carbon

• Lithotrophs:

  • Use inorganic compounds as electron/hydrogen donors.

  • Often autotrophic - using inorganic sources of electrons and CO2 as their inorganic carbon source

• This classification describes ELECTRON DONORS.

What are the four major microbial nutritional categories?

• Photoautotrophs: Light energy + inorganic carbon (CO₂). Example: Cyanobacteria, plants.

• Chemoautotrophs: Chemical energy + inorganic carbon (CO₂). Example: Nitrifying bacteria.

• Photoheterotrophs: Light energy + organic carbon. Example: Chloroflexus.

• Chemoheterotrophs: Chemical energy + organic carbon. Example: E. coli, animals.

What is the difference between chemolithotrophs and chemoorganotrophs?

• Chemolithotrophs:

  • Obtain energy from chemical reactions.

  • Use inorganic compounds as electron donors.

  • Often chemoautotrophic.

• Chemoorganotrophs:

  • Obtain energy from chemical reactions.

  • Use organic compounds as electron donors.

  • Often chemoheterotrophic.

• Carbon source and electron donor are separate classifications.

What are the two major forms of usable energy in microorganisms?

• Energy is stored and must be converted to a useful form

• Chemical energy: Stored in molecules such as ATP, which can transfer energy to cellular processes.

• Electrochemical energy: Stored as ion motive forces, involving ion concentration and electrical gradients across membranes.