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Acidobacteria: Candidatus Chloracidobacterium thermophilumOur lab, in collaboration with David Ward’s lab at Montana State University, has discovered a new phototrophic microorganism, Candidatus Chloracidobacterium thermophilum (Cab. thermophilum), with novel properties and that is the first phototrophic member of the bacterial phylum Acidobacteria. This is only the third time in the last 100 years that a new group of phototrophs has been discovered! Where did it come from?Cab. thermophilum was isolated from the phototrophic mats of Octopus Spring, an alkaline siliceous hot spring from the Lower Geyser basin of Yellowstone National Park.
What are some of its novel properties?Cab. thermophilum synthesizes chlorosomes (specialized light harvesting structures), the Fenna-Matthews-Olson (FMO) protein and type 1 reaction centers under oxic conditions, and makes bacteriochlorophylls a and c. The green sulfur bacteria and some Chloroflexi also synthesize chlorosomes but do so under anoxic conditions. Likewise, homodimeric type 1 reaction centers are present in the green sulfur bacteria and the heliobacteria, but both of these groups are strict anaerobes. This finding of an anoxygenic phototroph that grows phototrophically in the presence of oxygen is not only interesting but also will provide additional clues to the evolution of photosynthesis and aid in the design of artificial photosynthetic structures for light harvesting. How did we find it?Using PscA (a type 1 reaction center protein) as query, a BLASTP analysis of a metagenomic library from the Octopus and Mushroom Springs mats revealed the presence of a pscA gene that was distantly related to all other known pscA genes.
What other information did we obtain from the metagenomic library?Further analyses of the Octopus/Mushroom Springs metagenome, performed in collaboration with John Heidelberg from TIGR (now USC), revealed other genes that belong to Cab. thermophilum. For example, genes that code for enzymes involved in bacteriochlorophyll c biosynthesis, chlorosome-related proteins, and type 1 reaction center related proteins. In addition there were phylogenetic markers such as the 16S rRNA and the recA genes linked to pscA that placed this organism within the bacterial phylum Acidobacteria. Have the metagenome predictions been tested in functional studies?Yes. We have been able to isolate Cab. thermophilum in a mixed culture in which Cab. thermophilum is the dominant organism and the only phototroph present. By culturing this enrichment under light and dark treatments and monitoring growth through standard microbiological and molecular techniques we demonstrated that Cab. thermophilum is a phototroph. We have also isolated chlorosomes and are in the process of showing that it indeed produces a type 1 reaction center.
What experiments are we conducting now?We are learning more about this exciting microorganism by sequencing its genome (in collaboration with Drs. Cheryl Kuske and Chris Detter from the Los Alamos National Laboratory in New Mexico), and doing biochemical and ecological analyses. Biochemical analyses-chlorosomes: Articles of interest:
Links to articles about Cab. thermophilum and Yellowstone:http://www.science.psu.edu/alert/Bryant7-2007.htm http://www.nsf.gov/news/news_summ.jsp?cntn_id=109769 http://landresources.montana.edu/dward/ http://www.montana.edu/cpa/news/nwview.php?article=4997 Suppport from    |
