Microbial Photosynthesis

Microbial photosynthesis spans the oxygen-producing photosynthesis of cyanobacteria and the anoxygenic photosynthesis of several bacterial groups, processes that shaped the chemistry of the early Earth.

Definition

Microbial photosynthesis is the conversion of light energy into chemical energy by microorganisms, encompassing both oxygenic forms that release oxygen by splitting water and anoxygenic forms that use other electron donors.

Scope

This topic covers photopigments such as chlorophylls and bacteriochlorophylls; light harvesting and the photosynthetic reaction center; oxygenic photosynthesis in cyanobacteria with its two photosystems and water-splitting chemistry; anoxygenic photosynthesis in purple and green bacteria using a single photosystem and electron donors other than water; and the evolutionary and environmental significance of phototrophy.

Core questions

• How do photopigments capture light and initiate energy conversion?
• What distinguishes oxygenic from anoxygenic photosynthesis?
• How did cyanobacterial photosynthesis transform the early atmosphere?
• Which electron donors do anoxygenic phototrophs use instead of water?

Key concepts

• Chlorophylls and bacteriochlorophylls
• Light harvesting and reaction centers
• Oxygenic photosynthesis and water splitting
• Anoxygenic photosynthesis
• The Great Oxidation Event

Key theories

Comparative photosynthesis

Cornelis van Niel proposed a general framework in which photosynthesis uses light to drive the transfer of electrons from a donor to carbon dioxide, with water being only one possible donor, unifying oxygenic and anoxygenic forms.

Mechanisms

Photopigments absorb light and transfer the energy to reaction centers, where excitation drives electron transfer and the generation of a proton motive force for ATP synthesis. In oxygenic photosynthesis, two photosystems acting in series extract electrons from water, releasing oxygen, while in anoxygenic photosynthesis a single photosystem uses donors such as hydrogen sulfide or organic compounds, producing no oxygen.

Clinical relevance

Cyanobacterial photosynthesis is a major contributor to global primary production and oxygen supply, the rise of oxygenic photosynthesis profoundly altered Earth's atmosphere, and phototrophic microbes are of growing interest for bioenergy and carbon capture.

History

Cornelis van Niel's comparative studies of bacterial and plant photosynthesis in the early twentieth century revealed that water is the electron donor in oxygenic photosynthesis, while anoxygenic bacteria use other donors, a unifying insight that reframed the understanding of how light energy is harnessed.

Key figures

• Cornelis van Niel
• Sergei Winogradsky

Seminal works

• madigan2018
• willey2020

Frequently asked questions

What is anoxygenic photosynthesis?

Anoxygenic photosynthesis is a form of light-driven energy conversion carried out by certain bacteria that use electron donors other than water, such as hydrogen sulfide, and therefore do not produce oxygen. It uses a single photosystem rather than the two found in oxygenic phototrophs.