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Lecture 3

55-237 Lecture Notes - Lecture 3: Microscope Slide, Nitrifying Bacteria, Algae

Biological Sciences
Course Code
BIOL 2070

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Study guide for Topic 3: Growing microbes
1. Learning Objectives (LOs):
Students should be able to …
A. Nutritional and environmental factors
2. List and briefly describe the basic physical and chemical requirements for microbial growth.
[Knowledge, Comprehension]
- Temperature:
- Minimum growth temperature, optimum growth temperature, maximum growth temperature
- Psychrophiles (14)
- Psychotrophs (23); spoilage bacteria; mostly no pathogens grow at refrigerator temps
- Mesophiles (38)
- Thermophiles (62)
- Hyperthermophiles (95)
- pH:
- Most bacteria grow well between 6.5 and 7.5
- Acidophiles: tolerant to acidity
- Molds and yeast will grow over a greater pH range than bacteria (optimal: 5-6)
- Usually when grown bacteria produce acids… must be neutralized by use of buffered medium
- Use phosphate buffers
- Osmotic pressure:
- Hypertonic environment (cell plasmolysis; cell pulls away from the cell wall)
- Salt can be used to preserve foods
- Extreme halophiles
- Obligate halophiles (require high salt)
- Facultative halophiles
- Grow in salt concentrations of up to 2% (even up to 15%)
- Most organisms require 1.5% salt
- Carbon:
- Half of the dry weight of a typical bacteria is carbon
- Nitrogen, Sulfur and Phosphorus:
- Protein synthesis requires nitrogen and well as some sulfur
- Synthesis of DNA and RNA require nitrogen, phosphorus
- Some bacteria break down protein-containing material and reincorporate the amino acids
- Others get nitrogen from ammonium ions
- Others derive it from nitrates (NO3-)
- Some important bacteria can fix nitrogen (N2)
- Free living while others live cooperatively in symbiosis with roots
- Sulfur is used to synthesize amino acids and vitamins
- Sources include the sulphate ion (SO42-), H2S and sulfur-containing amino acids
- Phosphorus is needed for synthesis of nucleic acids and phospholipids, as well as ATP
- A source is the phosphate ion (PO43-)
- Potassium, magnesium and calcium are also required, often as cofactors
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Study guide for Topic 3: Growing microbes
- Trace elements:
- Iron, copper, molybdenum and zinc
- They are usually assumed to be present in tap water and other components of media
- Oxygen:
- Hydrogen atoms that have been stripped from organic compounds combine with O2 to form H2O
- Obligate aerobes: water is poorly soluble in water though
- Facultative anaerobes
- E. Coli
- Yeasts
- Many microbes are able to substitute other electrons acceptors such as nitrogen
- Obligate anaerobes
- Clostridium (tetanus and botulism)
- They use oxygen but not from molecular oxygen, but from water
- Don’t produce catalase or superoxide dismutase
- Aerotolerant anaerobes
- Many ferment carbohydrates to lactic acid
- Inhibits the growth of aerobic competitions and establish a favourable niche
- Common example: lactobacilli used in acidic fermented foods (pickles, cheese)
- Possess SOD or an equivalent system
- Microaerophiles
- Grow only in specific low oxygen concentrations
- Require oxygen, but are also oxygen sensitive (superoxide radicals and peroxides)
- Singlet oxygen (1O2-): normal O2 has been boosted into a higher-energy state (highly reactive)
- Superoxide radicals (O2-·): formed in small amounts during normal respiration
- They can steal an electron from a neighbouring molecule
- Obligate anaerobes form these in the presence of oxygen, which are toxic
- Aerobes (facultative) make an enzyme called superoxide dismutase (SOD)
- Convert the superoxide radicals into molecular oxygen and hydrogen peroxide
- Hydrogen Peroxide (H2O2): contains the peroxide anion (O22-) which is also toxic
- Catalase is present to convert it to water and oxygen
- Peroxidase can do the same job only produce just water from H2O2 and H+
- Hydroxyl radical (OH·): probably the most reactive
- Most aerobic respiration produces traces of it but they are transient
- Organic Growth Factors
- Must be directly obtained from the environment
- Vitamins act as coenzymes
- Many bacteria can synthesize their own!
- Other growth factors may include amino acids, purines and pyrimidines
3. Describe what is meant by macronutrients and micronutrients with respect to microbial chemical
growth requirements. [Comprehension, Application]
- Macronutrients: nutrients required in large amounts
- Micronutrients: chemical element or substance required in trace amounts for the normal
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Study guide for Topic 3: Growing microbes
4. Correctly categorize an organism’s mode of nutrition (using appropriate terminology), given
information about the source of energy, source of electrons, and/or source of carbon used.
[Knowledge, Comprehension, Application]
- Photoautotroph: light as energy source, CO2 as the carbon source
- Photosynthetic bacteria (green and purple bacteria and cyanobacteria)
- Hydrogen atoms of water are used to reduce carbon dioxide, oxygen gas is given out
- Sometimes called oxygenic
- There are others which are obligate anaerobes (anoxygenic)
- Green (use sulphur, H2S or H2 to oxidize to sulfate) and purple bacteria (reduce CO2 by
use of sulphur compounds)
- Photoheterotroph: light as energy source, organic carbon source
- Use alcohols, fatty acids, other organic acids and carbohydrates as a source of carbon
- They are anoxygenic
- Green nonsulfur bacteria and purple nonsulfur bacteria
- Chemoautotroph: oxidative-reduction reactions of inorganic/organic compounds for energy, CO2
- Use electrons from reduced inorganic compounds as a source of energy
- Such as H2S, S, NH3, nitrite ions (NO2-), H2, Fe2+, CO
- Use CO2 as their primary source of carbon (fix carbon in the Calvin-Benson cycle
- Energy derived from their oxidation is stored into ATP (oxidative phosphorylation)
- Chemoheterotroph: oxidative-reduction reactions of inorganic/organic compounds for energy, oC
- Usually the energy and carbon source are the same organic compound (glucose)
- Specifically use the electrons from hydrogen atoms in organic compounds as energy
- Saprophytes: live on dead organic matter
- Parasites: derive nutrients from a living host
5. Indicate which type(s) of organisms (i.e., bacteria, archaea, and major groups of eukaryotes) display
the various modes of nutrition. [Knowledge, Comprehension]
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