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minimum 16S rRNA sequence requirement

j.r.stephen mbi071 at sysc.abdn.ac.uk
Mon Jan 20 10:53:03 EST 1997


Hi David, 

As I tried to say in the email I sent you in reply to your query,(did you get 
it?) 
16S rDNA 
sequence is not a "gold-standard" by which species of bacteria can be defined at

a universally accepted level. The figure you are looking for is <97% homology, 
but it is still naive to claim species distinction on this level alone, and no 
referees will accept you trying to. It is an interesting and useful benchmark, 
but be very careful how you use it! Far better that you use the sequence 
information to extract phylogenetic information, showing how closely your 
sequence of interest relates to its nearest relatives. 

16S rDNA sequence data does not replace the need for physiological and 
morphological data, but of course I wish it did..... 

davadav at bitwise.net (davadav at bitwise.net) wrote:
: In article <5bfqeg$555 at mserv1.dl.ac.uk>, "g.clark" <g.clark at lshtm.ac.uk> wrote:

: >>>Perhaps the 'rules' are different for bacteria but I do not think species
: >>>should be described on the basis of rDNA alone. In eukaryotes there are
: >>>examples of bona fide biological species (i.e. unable to interbreed) of 
: >>>the ciliate Tetrahymena that have identical small subunit ribosomal RNA
: >>>sequences. Therefore identical sequence does not mean same species. 

: >>>
: >>>IMHO you need more than just sequence variation to warrant the 
: >>>recognition of a new species. But perhaps bacteriologists feel differently.
: >>>




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