Taxon-specific content of oligonucleotide triplets in 16S rRNAs of anoxygenic phototrophic and nitrifying bacteria

Theoretical evaluation of the content of oligonucleotide triplets AAA, CCC, and UAU in 16S rRNAs of anoxygenic phototrophic bacteria (genera Chlorobiu m; Chloroflexus; Chromatium; Rhodopseudomonas) and nitrifying bacteria (gen era Nitrosococcus, Nitrosomonas, Nitrosolobus, Nitrosovibrio, Nitrospira, N itrospina, Nitrobacter) showed that the number of the AAA, CCC or UAU tripl ets in 16S rRNAs specifically corresponds to the genus and species of bacte ria. The ratio of AAA and CCC triplet numbers in the sequences of 16S rRNA (AAA/CCC) of anoxygenic phototrophic bacteria was within the range of 0.61 to 2.03, and the ratio of AAA and UAU (AAA/UAU) triplet numbers in the sequ ence of 16S rRNA was within the range of 2.88 to 12.00. The regions of any genus within the AAA/CCC and AAA/UAU axes did not overlap. The combination of the numbers of nucleotide triplets in 16S rRNA is genus-specific charact er. The similar data were obtained in the study of a physiological group of nitrifying bacteria. The range of AAA/UAU ratio was from 1.8 to 9.0, and r ange of AAA/CCC was from 0.9 to 2.6 for this taxon. The number of triplets in 16S rRNAs of the studied taxa was genus- and species-specific character. The biological significance of these data is the evidence that not only th e sequence but the number of nucleotide triplets in 16S rRNAs reflects the phylogeny of corresponding taxa. (C) 1999 Academic Press.