A structural and phylogenetic analysis of the 16S rRNA of the Chlorobiaceae

Partial 16S rRNA sequences of 1212 and 943 nucleotides were determined for the green sulfur bacteria Chlorobium limicola and Pelodictvon luteolum by utilization of primer directed dideoxy sequencing with reverse transcriptase. The validity of the partial sequence data was verified, where possible, by the secondary structural model of eubacterial 16S rRNA, resulting in a relatively high degree of integrity for single strand sequencing. The previously available 16S ribosomal RNA catalogs for the green sulfur bacteria: Chlorobium limicola. Chlorobium vibrioforme, and Chioroherpeton thalassium were correctly aligned and in addition to aiding in verification of partial sequence data will in the future contribute to the continuing analysis of 16S rRNA structure. A secondary structure for the two green sulfur bacteria 16S rRNAs can be constructed that is essentially the same as that known for Escherichia coli. By proper alignment with an existing data base of 16S rRNAs a phylogenetic tree confirming the placement of the green sulfur bacteria as a unique group of photosynthetic organisms has been constructed, giving results that are in complete agreement with the catalog data for these organisms. The high degree of homology (95.9%) between the two partial sequences establishes the Chlorobiaceae as a closely knit, phylogenetically shallow, group of photosynthetic organisms.