Berkeley Lab, Caltech researchers debunk misconception about photosynthesis

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A study by Lawrence Berkeley National Laboratory and California Institute of Technology, or Caltech, debunks a common misconception about the origin of oxygen-producing photosynthesis.

Berkeley Lab postdoctoral fellow Patrick Shih, along with Woodward Fischer and Lewis Ward from Caltech, published the study online Sept. 18 and in the science journal Proceedings of the National Academy of Sciences on Oct. 3. The study disproved the idea that Chloroflexi bacteria were the precursors to oxygen-producing photosynthesis on Earth.

There are two types of photosynthesis: oxygenic, which is used by plants and algae and produces oxygen as a byproduct, and anoxygenic, which does not produce oxygen.

Cyanobacteria are theorized to be the evolutionary origin of oxygenic photosynthesis, according to Fischer.

“Before there’s cyanobacteria, there’s no oxygen on the planet,” Fischer said.

The study specifically looks at what came after the development of anoxygenic photosynthesis and before the speciation of cyanobacteria — prior to the study, many researchers generally believed that Chloroflexi bacteria did.

Often, Shih said in evolutionary biology, there is so little data that researchers “build stories” that align with their observations. This study was an opportunity to test the particular theory that Chloroflexi provided the evolutionary groundwork that allowed cyanobacteria to invent oxygenic photosynthesis — a theory that was rejected.

According to Shih, the study found that Chloroflexi bacteria were too evolutionarily young to have been this missing link. Shih said the missing link would be 2.5 billion years old, but Chloroflexi bacteria is only about 867 million years old.

The study involved molecular clock analysis, which is used to reconstruct evolutionary history. Using this method, Fischer, Shih and Ward could determine how many mutations occur in a genome over a period of time, and they mapped where organisms lie on a phylogenetic tree based on similarities and differences between their genomes. After this molecular analysis, researchers determined that Chloroflexi were much younger than they expected.

Going forward, Fischer describes two options: Whatever came before cyanobacteria is either alive or extinct.

If it is extinct, he said it may be difficult for researchers to find in fossil records. If it is alive, however, there isn’t a targeted way for researchers to look for it. For now, Fischer said researchers will continue to sequence different samples from different environments, and whenever a new photosynthetic organism is discovered, they will determine where it sits in the evolutionary tree of life.

Contact Matthew Lo at [email protected] and follow him on Twitter at @matthewlo_dc.

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  • Willliam Wallace

    Isn’t anyone looking at devolution, the retrogression of evolution? That could describe the phenomenon by which people of ordinary intelligence and potential give rise to regressive offspring which currently comprise campus republicans, trumpanzees and Ayn Rand acolytes.

  • Oxygenic photosynthesis is much older than 2.5, or even 3.5 billion years;

    Nutman, A.P., Bennett, V.C., Friend, C.R., Van Kranendonk, M.J. and Chivas, A.R.,
    2016 “Rapid emergence of life shown by discovery of 3,700-million-year-old microbial structures” Nature, 537(7621), pp.535-538. Isua stromatolites

    Manfred Schidlowski, Peter W. U. Appel, Rudolf Eichmann and Christian E. Junge
    1979 “Carbon isotope geochemistry of the 3.7 × 10^9-yr-old Isua sediments, West Greenland: implications for the Archaean carbon and oxygen cycles” Geochim. Cosmochim. Acta 43, 189-199

    Rosing, Minik T. and Robert Frei
    2004 “U-rich Archaean sea-floor sediments from Greenland – indications of >3700 Ma oxygenic photosynthesis” Earth and Planetary Science Letters, 217: 237-244 (online 6 December 03)

  • Killer Marmot

    It’s find to say that some new scientific result challenges or overturns a previous idea. Saying that it “debunks a misconception”, however, is not the best way to put it.