<Tr> <Td> 27F </Td> <Td> AGA GTT TGA TCM TGG CTC AG </Td> <Td> </Td> </Tr> <Tr> <Td> 1492R </Td> <Td> CGG TTA CCT TGT TAC GAC TT </Td> <Td> as above </Td> </Tr> <P> In addition to highly conserved primer binding sites, 16S rRNA gene sequences contain hypervariable regions that can provide species - specific signature sequences useful for identification of bacteria . As a result, 16S rRNA gene sequencing has become prevalent in medical microbiology as a rapid and cheap alternative to phenotypic methods of bacterial identification . Although it was originally used to identify bacteria, 16S sequencing was subsequently found to be capable of reclassifying bacteria into completely new species, or even genera . It has also been used to describe new species that have never been successfully cultured . With Third - generation sequencing coming to many labs, simultaneous identification of thousands of 16S rRNA sequences is possible within hours, allowing metagenomic studies, for example of the gut flora . </P> <P> The bacterial 16S gene contains nine hypervariable regions (V1 - V9) ranging from about 30 - 100 base pairs long that are involved in the secondary structure of the small ribosomal subunit . The degree of conservation varies widely between hypervariable regions, with more conserved regions correlating to higher - level taxonomy and less conserved regions to lower levels, such as genus and species . While the entire 16S sequence allows for comparison of all hypervariable regions, at approximately 1500 base pairs long it can be prohibitively expensive for studies seeking to identify or characterize diverse bacterial communities . These studies commonly utilize the Illumina platform, which produces reads at rates 50-fold and 12,000-fold less expensive than 454 pyrosequencing and Sanger sequencing, respectively . While cheaper and allowing for deeper community coverage, Illumina sequencing only produces reads 75 - 150 base pairs long (250 to 300 base pairs with Illumina MiSeq), and has no established protocol for reliably assembling the full gene in community samples . Full hypervariable regions can be assembled from a single Illumina run, however, making them ideal targets for the platform . </P>

What does the s stand for in 16s rrna