Light-harvesting Bacterium Discovered in Yellowstone
Posted on July 26, 2007 Comments (4)
Remarkably, the new genus and species Cab. thermophilum also belongs to a new phylum, Acidobacteria. The discovery marks only the third time in the past 100 years that a new bacterial phylum has been added to the list of those with chlorophyll-producing members. Although chlorophyll-producing bacteria are so abundant that they perform half the photosynthesis on Earth, only five of the 25 major groups, or phyla, of bacteria previously were known to contain members with this ability.
“The microbial mats give the hot springs in Yellowstone their remarkable yellow, orange, red, brown and green colors,” explained Bryant. “Microbiologists are intrigued by Octopus and Mushroom Springs because their unusual habitats house a diversity of microorganisms, but many are difficult or impossible to grow in the lab. Metagenomics has given us a powerful new tool for finding these hidden organisms and exploring their physiology, metabolism and ecology.”
Unexpectedly, the new bacterium has special light-harvesting antennae known as chlorosomes, which contain about 250,000 chlorophylls each. No member of this phylum nor any aerobic microbe was known to make chlorosomes before this discovery. The team found that Cab. thermophilum makes two types of chlorophyll that allow these bacteria to thrive in microbial mats and to compete for light with cyanobacteria.
This discovery is particularly important because members of the Acidobacteria have proven very hard to grow in laboratory cultures, which means their ecology and physiology are very poorly understood. Most species of Acidobacteria have been found in poor or polluted soils that are acidic, with a pH below 3. However, the Yellowstone environments are more alkaline, about pH 8.5 (on a scale of 1 to 14). Bryant noted, “Judging from their 16S rRNA sequences, the closest relatives of Cab. thermophilum are found around Mammoth Hot Springs in Yellowstone and hot springs in Tibet and Thailand. As we look more closely, we may find relatives of Cab. thermophilum in the microbial mats of thermal sites worldwide.”
Photo of Mammoth Hot Springs, Yellowstone National Park by John Hunter.