Old Life Capable Of Revealing New Tricks After All

Archaea are among the oldest known life-forms, but they are not well understood. It was only in the 1970s that these single-celled microorganisms were designated as a domain of life distinct from bacteria and multicellular organisms called eukaryotes. Robert Gunsalus, a UCLA professor of microbiology, immunology and molecular genetics, developed an interest in Archaea because of their ability to thrive in harsh environments. Now, using state-of-the-art imaging equipment at the California NanoSystems Institute (CNSI) at UCLA, he has shown for the first time that a type of Archaea known as Methanosprillum hungatei contains incredibly efficient energy-storage structures.

The findings are published in the current issue of the journal Environmental Microbiology.

M. hungatei is of considerable environmental significance because of its unique ability to form symbiotic relationships with syntrophic bacteria to break down organic matter and produce methane gas. Yet while their important role in the food chain has been studied, little has been known about how they generate and store energy.

Gunsalus has researched anaerobic organisms like M. hungatei — microbes that thrive in oxygen-depleted environments where energy is often extremely limited — for a number of years. And when Hong Zhou, a professor of microbiology, immunology and molecular genetics, arrived at UCLA in 2006, Gunsalus saw an opportunity to delve further into their mysteries.

"When Hong came to UCLA, his reputation in imaging nanoscale structures was already well established," said Gunsalus, who is also a member of the UCLA–Department of Energy Institute for Genomics and Proteomics. "His arrival on campus brought together the expertise to do what no one had yet done — a detailed study of the sub-cellular structures in M. hungatei."

Much of the actual imaging work for the study was performed by Dan Toso, a graduate student in Zhou's lab, using equipment from the Electron Imaging Center for Nanomachines (EICN), a core lab at the CNSI directed by Zhou. When Toso and the rest of the team produced the most detailed images yet made of the M. hungatei interior, they were surprised by the appearance of granules, structures measuring approximately 150 nanometers in diameter that store energy.

"Once we imaged the M. hungatei, we noticed how dark the granules appeared," said Zhou, a researcher at the CNSI. "The darkness arises from their density, and by studying this density, we discovered their energy-storage capacity."