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Bacterial discovery raises questions on plant evolution

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Researchers at the Welander Lab discovered bacteria that produce a fatty molecule thought only to exist in flowering plants, forcing scientists to re-evaluate the molecule as an indicator of past plant life and revealing new paths to synthesize these molecules.

The Welander Lab uses microbiology genomics to address questions in the geosciences. It deals with molecules called biomarkers, which are molecular degradation products that indicate the past presence of certain lifeforms.

Co-author of the study, Paula Welander, a geobiologist at Stanford’s School of Earth, Energy and Environmental Sciences, said that this breakthrough addresses open questions on genetic history.

“One of the big problems that we’ve had in this biomarker world is that we’re not always sure if we’ve detected all the potential organisms that could make a potential lipid,” Welander said. “How do you correlate the presence of this one molecule to an organism and what does that tell you if you see it being produced in an organism today?”

The biomarker in question is isoarborinol, a fatty molecule found only in flowering plants before this study. Previously, this biomarker produced incongruities when found in fossil records dating from before the evolution of flowering plants. The discovery of an isoarborinol-like molecule from bacteria explains some of these incongruities.

The project initially started as a study of sterol, a different biomarker thought to only be produced by eukaryotes. In an attempt to find prokaryotic sources of sterol, Welander lab researchers looked in genetic databases for organisms that produced cyclase proteins, which are involved in the first step of producing sterols. They discovered cyclase protein in a marine bacterium called Eudoraea adriatica and detected an unidentified molecule along with the sterols.

After the discovery, Welander consulted with her postdoctoral advisor, Roger Summons. Summons is a professor of geobiology at MIT who was on sabbatical at Stanford.

“Roger is a walking spectral library,” Welander said. “He’s studied these molecules for 20 to 30 years and he knows a lot… He’d never seen [this molecule]. He didn’t have a record of it.”

After collaborating with José-Luis Giner, an associate professor of chemistry at the State University of New York and a co-author of this paper, the team realized that the molecule belonged to a class of molecules called triterpenols. Theirs was the first triterpenol discovery in over 30 years.

The discovery of this molecule in bacteria and of the proteins that produce it introduce molecular mechanisms of production that differ from those in flowering plants. Connecting this molecular product with new proteins allows the Welander lab to study whether different organisms whose genes encode for the protein also produce isoarborinol-like molecules.

“By using the genes to identify these molecules, [we] can find novel things that we hadn’t been looking for before,” said Welander.

Contact Aulden Foltz at afoltz ‘at’ stanford.edu.