Week 5 Microbial Growth + Cell Cycle

Question 1

Microbial Diversity

Answer 1

Guild 1:
> Methanogen and Acetogens (CO2 –> CH4 and acetate)
Guild 2:
> Sulfate and sulfur-reducing bacteria (SO4 and S0 –> H2S)
Guild 3:
> Denitrifying bacteria (NO3 –> N2)
> Ferric iron-reducing bacteria (Fe3+ –> Fe+)
Guild 4:
> Fermentative bacteria

Question 2

Microbial Cell Morphologies

Answer 2

1. Coccus (biodegradation, marine cyanobacterium)
2. Rod (TB pathogen)
3. Spirillum and Spirochete
4. Filamentous bacteria, budding and square

Question 3

Surface-to-volume ratios

Answer 3

1. High S/V ratio of smaller cells support greater nutrient exchange
2. Smaller cells grow faster and can outcompete eukaryotic microbes

Question 4

Cell Growth and Binary Fission

Answer 4

Single generation: all cellular components increase proportionately to allow existence of independent daughter cell

Question 5

Prokaryotic Population Growth

Answer 5

1. Increase in number of cells in a population
   > Fast: < 20 minutes (E. Coli in rich media at RT)
   > Slow: 20+ years (oligotrophic cyanobacteria)

Question 6

Microbial Growth Cycle

Answer 6

OD increases overtime but declines eventually
> Lag: synthesis of cellular components before growth
> Exponential: cell division in healthiest state (2x)
> Stationary: nutrients depleted and wastes accumulated
> Death: cell lysis (reduction in turbidity)

Question 7

Measuring Microbial Growth

Answer 7

1. Direct microscopic counting
2. Viable counting (add cells –> spread –> count surface colonies)
3. Turbidity measurements: OD (light through filter to detector –> spectrophotometer)

Question 8

Microbial Nutrition

Answer 8

1. Nutritional Consideration
   > Macronutrients, trace elements, cofactors/vitamins
2. Simple Energetics
   > Redox, NAD coenzyme electron carriers, energy-rich compounds
3. Culture media
   > Defined and complex