When hunting for secrets into the life and times of early complex microscopic organisms on earth, biomarkers are indispensable guides.
Phylogenetic tree showing the relationsip between OlsG and known bacterial lipid N-methyltransferases.

If we can reconstruct the activities of ancient microbial communities, we may gain new insights into phenomena such as the drivers that underpin mass extinction events.

MIT Professor Roger Summons has spent much of his career uncovering and analyzing biomarkers—natural products that can be traced to a specific biological origin. Biomarkers are important because they help researchers trace diseases, drugs, and environmental contaminants. They also shed light onto ancient environments and the evolution of life on our planet.

“In much the same way that rock specimens provide us with a geological record, the most useful biomarkers have persistent structures that give us a molecular fossil record,” explains Summons. “We can open new windows on the history of earth’s climate if we can increase our understanding of how the biogeochemistry of organisms adapt to changes in the environment.”

Summons used an MIT-Mexico CONACYT Seed Fund grant to collaborate with National Autonomous University of Mexico (NAUM) Professor Otto Geiger and MIT Postdoc Associate Florence Schubotz on a project to investigate a promising new biomarker. “We already knew that certain types of lipids help organisms adapt to evolving climate conditions,” Summons says, “and we’ve learned in recent years that aminolipids are particularly abundant in marine environments such as the open ocean. Our goal was to identify novel organisms that synthesize aminolipids and unravel their physiological functions.”

The team used a two-pronged approach—lab-based culture studies of relevant bacteria known to synthesize, or have the genetic potential to synthesize, aminolipids and environmental surveys of aminolipids and related genes that could be linked to specific organisms. Summons explains that “by looking at contemporary microbes, we can identify products that we would expect to be preserved in ancient sediments over geological history. Armed with that information, we can begin to describe the characteristics of long gone microbial communities. We should, for example, be able to read the chemical record of the prelude to and recovery from catastrophic events such as mass extinctions.”

During the project, the MIT-Mexico team discovered a new type of aminolipid modification and the species of planctomycete (Singulisphaera acidiphila) in which that modification occurs. “The basic science of our findings is interesting in and of itself,” says Summons, “but we also are thrilled by how this will help us in a paleobiological sense. Aminolipids can be more stable than other types of molecules we find in sedimentary records, and we can trace their responses to dramatic climate stresses. As we continue this work, we expect to gain new insights about the environments in which some lifeforms thrived—then perished.”

Read the paper on Orinthine lipid modification in the planctomycete Singulisphaera acidiphila that resulted from Roger Summons’ MISTI award.

  • Mexico
  • Seed Fund
  • EAPS