158. The Chlorobium tepidum Genome Sequencing Program at TIGR  

Karen A. Ketchum, Matthew D. Cotton, Cheryl Bowman, M. Brook Craven, Tanya Mason, Terrence Shea, William Nierman, and Claire M. Fraser  
The Institute for Genomic Research, 9712 Medical Center Drive, Rockville, Maryland 20850  
kketchum@tigr.org 

The genus Chlorobium is placed in the taxonomic group of green sulfur bacteria (Chlorobiaceae). They are formally classified as Gram-negative organisms. Members of this genus are photoautotrophs that can generate chemical energy through an electron transport chain in the cytoplasmic membrane that is associated with a light-harvesting complex housed in a specialized organelle called the chlorosome. The components of this light-harvesting apparatus and some of its organizational structure are reminiscent of photosystems found in plant chloroplasts and, therefore, the evolutionary relationship of these prokaryotes to eukaryotic organelles is of interest. Chlorobium species can also fix CO₂, although the biochemical pathway used by these prokaryotes is distinct from the Calvin cycle found in higher plants. 

C. tepidum was initially identified from a hot spring in New Zealand (Wahlund et al. 1991). This species is thermophilic with and optimum growth temperature of @ 47C. It has a genome size of 2.1 Mb (Naterstad et al., 1995) with a G + C content of 56.5 mol%. C. tepidum was nominated for sequencing by the DOE because it has a prominent role in global carbon cycling and an interesting phylogenetic position in the Eubacterial kingdom. 

The C. tepidum genome project was initiated in March of 1998. Genomic DNA was generously supplied by Dr. Donald A. Bryant, Earnest C. Pollard Professor of Biotechnology and Professor of Biochemistry and Molecular Biology at The Pennsylvania State University. Random sequencing of a small insert (1.6 - 2.5 kb) plasmid library began in May and is now complete. We obtained 32,246 sequencing reads for 8X coverage of the genome. The overall success rate was 82%. We are now sequencing a large insert lambda library which will provide linking information for our contigs. The current genome assembly has 41 groups with 38 sequencing gaps and 80 physical gaps. A progress report on the C. tepidum project will be presented.