New light-harvesting bacterium found in microbial mats of Yellowstone

Heat-loving bacterium that reveals a new way to harvest light energy has been discovered in the colourful microbial mats of Octopus Spring in Yellowstone National Park. Image credit: David Strong/Pennsylvania State University
Date:30 July 2007 Tags:

A heat-loving bacterium that reveals a new way to harvest light energy has been discovered in the colourful microbial mats around the hot springs of Yellowstone National Park. This is only the third time in 100 years that scientists have found a new group of bacteria that transfers sunlight into chemical energy.

This organism provides insights into the history of photosynthesis and increases our knowledge of how solar energy is captured in this microbial community, said Dave Ward, a Montana State University (MSU) professor who co-authored the paper published on 27 July in the journal Science. “Thus, this bacterium may have implications for alternative fuels.”

Of the 25 major groups of bacteria in the world, only five were known to make chlorophyll and perform photosynthesis, Ward said. Then scientists found Candidatus Chloracidobacterium thermophilium in the microbial mats that reside in the outflows of Mushroom Spring and Octopus Spring, located almost 13 km north of Old Faithful. The newly-found bacterium belongs to a group, called Acidobacteria. Ward said no one was aware that this group, which contains as much diversity as the plant kingdom does, included bacteria that could use light energy for growth.

In the course of conducting research, MSU scientists sampled the Mushroom mats in October 2003 and the Octopus mats in November 2004. The samples were used to generate large DNA databases, called metagenomes, which contain genes from organisms inhabiting the mat. Lead author, Don Bryant from the Pennsylvania State University (Penn State), discovered the first evidence of this unexpected and significant organism by analysing these databases.

Metagenomics allows scientists to study organisms without growing cultures in the laboratory. The researchers gather samples from the field, isolate DNA from the cells and go from there. Ward said that the discovery of the new bacterium could have only come through genetic study because individual bacteria from the mat all look alike under a microscope.

Said Bryant in a press release from Penn State: “Octopus and Mushroom Springs are intriguing to microbiologists because their unusual habitats are homes to a diversity of micro-organisms, but many of them have proven difficult or impossible to grow as pure cultures in the lab. Metagenomics has given us a powerful new tool for finding these hidden organisms and exploring their physiology, metabolism and ecology.”

The new bacterium grows near the surface of the microbial mats where the temperature ranges from 50 to 66 degrees Celsius. It competes for light with cyanobacteria (formerly called blue-green algae) and other bacteria, but contains so much chlorophyll that it thrives in that environment, Ward said. Each cell contains tens of millions of chlorophyll molecules.

Ward said the microbial mats where the bacterium was found consist of layers. The mats are found in springs emitting water that became alkaline by interacting with volcanic ash and lava flows inside Yellowstone’s caldera. The mats look yellowish orange in the summer and greener in the winter.

“Finding a previously unknown, chlorophyll-producing microbe is the discovery of a lifetime for someone who has studied bacterial photosynthesis for as long as I have (35 years),” said Bryant. “I wouldn’t have been as excited if I had reached into that mat and pulled out a gold nugget the size of my fist!”

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