FINAL Week 6 Microbial Trophic Dynamics

Question 1

Physiological/Ecological Diversity

Answer 1

Guild 1:
> Methanogen (CO2 ---> CH4)
> Acetogens (CO2 --> acetate)
Guild 2:
> Sulfate-reducing (SP42- --> H2S)
> Sulfur-reducing (S0 --> H2S)
Guild 3:
> Denitrifying (NO3 --> N2)
> Ferric iron-reducing (Fe3+ --> Fe+)
Guild 4:
> Fermentative bacteria

Question 2

Macronutrients vs Micronutrients

Answer 2

Macro:
> C (50% of cell by dry weight)
> N (12%): protein/nucleic acid
> S (AA like Met and Cys) P, K, Mg, Ca, Fe
Micro:
>Cu, Mn, Ni, Co, Zn (enzyme cofactors)

Question 3

Heterotrophic energy access and nutrient sources

Answer 3

1. Osmotrophy: uptake of dissolved organic matter (DOM)
2. Ectoenzymes: EC enzymatic degradation of particulate organic matter (POM)
   > Glycosidases, proteases, lipases, glucanases
3. Biosurfactants:
   > Excreted emulsifying agents enhancing hydrocarbon availability and mobility
   > Alter surface tension at oil:water interface
4. Siderophores: excreted compounds chelating ions for cell transport
   > Oxic: Fe complexed in mineral phases (no access; usually highly limited)
   > Fe sequested by IS and acute phase responses during infection to limit bacterial growth
   > Fe3+ + hydroxamate –> ferric hydroxamate enters cell wall/cytosol –> e- reduction –> Fe2+ (hydroxamate leaves)

Question 4

Phototrophic Energy access and Energy Sources (Redox-active chromophores)

Answer 4

1. Oxygenic: evolve O2
   > Cyanobacteria, plants: 2 photosystems with chlorophyll a + accessory pigments
   > *Calvin-Benson Cycle
2. Anaerobic/anoxygenic:
   > purple green sulfur/non-sulfur bacteria and heliobacteria: 1 photosystem with bacteriochlorophyll a-g + carotenoids4
   > *Reverse TCA, hydroxyproprionate pathway
   * CO2 fixation pathways

Question 5

Global Carbon Cycle

Answer 5

Majority due to microbial respiration and decomposition
> Net CO2 fixation (photosynthesis) + respiration
> Oxy: CO2 –> organic matter via photosynthesis and chemolithotrophy (from inorganic compounds)
> Anoxy: CO2 –> organic matter via acetogenesis, methanogenesis

Question 6

Aerobic Respiration

Answer 6

*Further down redox tower –> more energy released
1). Glycolysis: glucose is e- donor and 2 NADH is e- carrier to Complex I
> Substrate-level (2 ATP) and OxPhos (6 ATP; O2 as e- acceptor)
2). CAC: 4 NADH and FADH to complex I and II
Sum: 38 ATP/glucose (efficient system)

Question 7

NAD Coenzyme: Redox e- Carrier

Answer 7

Path from glucose to CO2
> NAD+/NADH and NAD-phosphate (NADP+/NADPH)
> Enzyme I interacts with e- donor (glucose) and oxidized form of coenzyme (NAD+)
> Enzyme II interacts with e- acceptor and reduced form of coenzyme (NADH)