10.3 Microbial Physio Module 10: Fermentation & Photosynthesis

Which bacteria use the reverse tricarboxylic acid (TCA) cycle for CO₂ fixation?

• Chlorobium limicola

• Escherichia coli

• Rhodopseudomonas palustris

• Clostridium acetobutylicum

Answer explanation

Answer: a. Green sulfur bacteria like Chlorobium use the reverse TCA cycle for carbon fixation

References:

Brock et al., 2021

Kang, W., Suzuki, M., Saito, T., & Miyado, K. (2021). Emerging role of TCA Cycle-Related Enzymes in human diseases. International Journal of Molecular Sciences, 22(23), 13057. https://doi.org/10.3390/ijms222313057

Which bacterial photosynthetic pathway does not involve the production of oxygen?

• Anoxygenic photosynthesis

• Oxygenic photosynthesis

• Chemolithotrophy

• Oxidative phosphorylation

Answer explanation

Answer: a. Anoxygenic photosynthesis, seen in Rhodobacter species, does not produce oxygen

References:

Brock et al., 2021

Struck & White, 2019

What is the role of quinones in bacterial photosynthesis?

• Light absorption

• ATP hydrolysis

• Electron transfer

• Carbon fixation

Answer explanation

Answer: c. Quinones transfer electrons between complexes in the bacterial electron transport chain

Reference:

Brock et al., 2021

What type of metabolism combines photosynthesis and nitrogen fixation in bacteria?

• Phototrophy

• Chemotrophy

• Photoautotrophy

• Photoheterotrophy

Answer explanation

Answer: c. Photoautotrophic bacteria, such as Anabaena, can fix nitrogen and perform photosynthesis

References:

Struck & White, 2019

Volgusheva, A., Kosourov, S., Lynch, F., & Allahverdiyeva, Y. (2019). Immobilized heterocysts as microbial factories for sustainable nitrogen fixation. Journal of Biotechnology, 306, 100016. https://doi.org/10.1016/j.btecx.2020.100016

Which bacteria thrive in light-exposed, anoxic environments?

• Rhodobacter species

• Escherichia coli

• Clostridium botulinum

• Pseudomonas aeruginosa

Answer explanation

Answer: a. Rhodobacter species are phototrophic bacteria found in environments without oxygen

References:

Brock et al., 2021

Imam, S., Yilmaz, S., Sohmen, U. et al. iRsp1095: A genome-scale reconstruction of the Rhodobacter sphaeroides metabolic network. BMC Syst Biol 5, 116 (2011). https://doi.org/10.1186/1752-0509-5-116

What is a by-product of bacterial oxygenic photosynthesis?

• Sulfate

• Methane

• Oxygen

• Ethanol

Answer explanation

Answer: c. Oxygen is a by-product of oxygenic photosynthesis in Cyanobacteria

Reference:

Brock et al., 2021

Which process occurs in the purple sulfur bacteria to generate ATP?

• Non-cyclic photophosphorylation

• Cyclic photophosphorylation

• Substrate-level phosphorylation

• Fermentation

Answer explanation

Answer: b. Purple sulfur bacteria use cyclic photophosphorylation to produce ATP

References:

Forti, G., Rosa, L. (1972). Cyclic Photophosphorylation. In: Forti, G., Avron, M., Melandri, A. (eds) Photosynthesis, two centuries after its discovery by Joseph Priestley. Springer, Dordrecht. https://doi.org/10.1007/978-94-010-2938-4_39

Struck & White, 2019

https://byjus.com/biology/cyclic-photophosphorylation/

Which gas inhibits nitrogenase activity in nitrogen-fixing photosynthetic bacteria?

• CO₂

• O₂

• H₂S

• N₂

Answer explanation

Answer: b. Oxygen inhibits nitrogenase, the enzyme responsible for nitrogen fixation

Reference:

Allen, J. F., Thake, B., & Martin, W. F. (2019). Nitrogenase inhibition limited oxygenation of Earth’s proterozoic atmosphere. Trends in Plant Science, 24(11), 1022–1031. https://doi.org/10.1016/j.tplants.2019.07.007

Brock et al., 2021

Which bacterial photosynthesis pigment absorbs light maximally in the far-red region?

• Bacteriochlorophyll g

• Chlorophyll a

• Phycoerythrin

• Carotenoid

Answer explanation

Answer: a. Bacteriochlorophyll g absorbs light in the far-red spectrum, enabling deep water photosynthesis

References:

Brock et al., 2021

Tsukatani, Y., & Tamiaki, H. (2019). In vitro and In vivo Synthesis of Bacteriochlorophyll Absorbing Near-Infrared Light. In Series on chemistry, energy and the environment (pp. 1–17). https://doi.org/10.1142/9789813274440_0001

Which bacterium performs both anoxygenic photosynthesis and hydrogen production?

• Rhodopseudomonas palustris

• Escherichia coli

• Lactobacillus acidophilus

• Methanosarcina

Answer explanation

Answer: a. Rhodopseudomonas palustris performs anoxygenic photosynthesis and produces hydrogen under anaerobic conditions

References:

Larimer, F., Chain, P., Hauser, L. et al. Complete genome sequence of the metabolically versatile photosynthetic bacterium Rhodopseudomonas palustris. Nat Biotechnol 22, 55–61 (2004). https://doi.org/10.1038/nbt923

Struck & White, 2019