Photosynthetic bacterium discovered

Although Yellowstone National Park is a popular tourist destination, it is also home to diverse flora and fauna. Within its hot springs, scientists from Pennsylvania State University in University Park and from Montana State University in Bozeman have discovered a chlorophyll-producing bacterium, “Candidatus Chloracidobacterium thermophilum.”

Only two other phototrophic bacteria species have been identified in 100 years, and only five of the 25 bacterial phyla were known to harvest light energy using chlorophylls, although they account for half the world’s photosynthesis.

Researchers discovered a species of chlorophyll-producing bacteria in microbial mats growing on top of this hot spring and on two others in Yellowstone National Park.

Although it is easy to see colorful microbial mats growing on top of the hot springs, it can be difficult to culture and isolate bacteria from these mats in the laboratory, according to the researchers. Instead, they obtained a field sample of a mat, and they harvested and sequenced the DNA from all of the microorganisms in it. Once the sequences were entered into a computer, they used the computer to search for pscA, a gene necessary for photosynthesis, and for 16S ribosomal RNA, a gene that marks distinct species.

Once they found both genes in the same genome among the computer results, they surmised that they had a unique species with light-harvesting ability. These results were verified when the researchers isolated a single DNA fragment containing both genes and when they isolated and studied the bacterium, as reported in the July 27 issue of Science. They further determined that the bacterium makes two types of chlorophyll, bacteriochlorophyll a and c.

The researchers also discovered that Cab. thermophilum has chlorosomes, special light-harvesting antennae that each contain ~250,000 chlorophyll molecules. This species is the first in its phylum and the first aerobic microbe found to have these specialized appendages.