Sir

Following calls for online taxonomic databases encompassing all organisms living on Earth1,2,3,4, we wish to point out that extensive taxonomic information on the prokaryotes is already available online. The Approved Lists of Bacterial Names, including names and their nomenclatural history, are on a website that is updated bimonthly (http://www.bacterio.cict.fr). On 9 July 2002 the lists named 5,866 species, classified in 1,104 genera, Archaea and Bacteria combined. Comprehensive information on prokaryote taxonomy is in two handbooks, The Prokaryotes and Bergey's Manual of Systematic Bacteriology, both published by Springer-Verlag. The former is published online (http://www.link.springer.de/link/service/books/10125), and the database of the second edition of the latter (http://www.cme.msu.edu/bergeys) exists in electronic form, so could easily be made available on the web if the publisher gives permission.

In the case of the prokaryotes, obstacles virtually unknown to the botanist and the zoologist must be overcome to achieve the goals mentioned by Gewin and others. First, the species concept for bacteria is still not well-defined5,6. Second, sequencing of 16S ribosomal RNA genes collected from terrestrial and aquatic environments shows that the number of known prokaryotic species probably forms only a fraction of 1% of the number in nature. Morphological diversity is small, and therefore digital images of type specimens are of little help in online taxonomic databases. The lack of innovative culturing techniques and of well-trained taxonomists to study the isolates are of great concern. Some of the most abundant prokaryotes on Earth defy microbiologists' attempts to isolate them. Here lies one of the major challenges to future taxonomists.