On species descriptions based on a single strain: proposal to introduce the status species proponenda (sp. pr.).

A survey of the descriptions of novel bacterial species published in the period 1996–2006revealed that a large number of taxonomic descriptions are still based on one or a few strains. Thissituation determines that not only species descriptions, but also proposals to create higher ranks,are actually based on very few strains, which could produce a highly biased scenario. Theencouragement to include a reasonable number of strains in species descriptions has beenlargely disregarded after its proposal, since acceptance of such descriptions relies mainly oneditors’ and reviewers’ opinions. This observation and other considerations lead us to propose thecreation of the status species proponenda (sp. pr.), as a compromise between the need forscientific description of biodiversity and exchange of data and the good taxonomic practice ofincluding a sufficient number of strains in descriptions of species and higher taxonomic ranks.Christensen et al. (2001) presented a detailed report on thetrend of describing novel taxonomic units (species, generaand families) based on a very small number of isolates oreven one isolate. This is not considered good taxonomicpractice, since descriptions based on single isolates mightnot be reliable and good theoretical reasons to includemany isolates in taxonomic studies have been documented(Sneath, 1976; Tru¨per & Schleifer, 1992).With this premise, Christensen et al. (2001) suggestedthat Recommendation 30b of the International Code ofNomenclature of Bacteria (the Bacteriological Code; Lapageet al., 1992) be modified as follows: ‘Descriptions should bebased on as many strains as possible (minimum five),representing different sources with respect to geographyand ecology in order to be well characterized bothphenotypically and genotypically, to establish the centre(from which the type strain could be chosen) and theextent of the cluster to be named. In addition, comparativestudies should be performed, including reference strainsthat represent neighbouring species and/or genera, in orderto give descriptions that are sufficiently detailed to allowdifferentiation from these neighbours’.On this basis, the ad hoc committee for the re-evaluation ofthe species definition in bacteriology encouraged microbiologiststo base a species description on more than asingle strain (Stackebrandt et al., 2002).We performed a review of the descriptions of novel speciesand genera published between 1996 and 2006. Lists ofnames published each year were obtained from J. P.Euze´by’s List of Prokaryotic names with Standing inNomenclature, in particular from http://www.bacterio.cict.fr/allnamesac.html for names validly published in1996 and 1997 and from specific yearly lists for the years1998–2006 (1998, http://www.bacterio.cict.fr/twothousand/ninetyeight.html; 1999, http://www.bacterio.cict.fr/twothousand/ninetynine.html; 2000, http://www.bacterio.cict.fr/twothousand/changestwothousand.html; 2001, http://www.bacterio.cict.fr/twothousand/twothousandone.html; 2002, http://www.bacterio.cict.fr/twothousand/twothousandtwo.html; 2003,http://www.bacterio.cict.fr/twothousand/twothousandthree.html; 2004, http://www.bacterio.cict.fr/twothousand/twothousandandfour.html; 2005, http://www.bacterio.cict.fr/twothousand/twothousandfive.html; 2006, http://www.bacterio.cict.fr/twothousand/twothousandsix.html).Descriptions of new combinations, new subspecies andCandidatus were omitted, as well as descriptions of novelhigher taxonomic ranks that did not contain novelspecies. The results of the analysis are reported in Fig. 1;species numbers are plotted for each year according to thenumber of strains which was included in the originaldescription.It is evident that, after the ‘encouragement’ of 2002, thetrend of taxonomic descriptions has not changed, witheven an increase in the incidence of proposals of novelspecies based on one or a few strains. It could therefore beconcluded that the suggestion of the ad hoc committee(Stackebrandt et al., 2002) was not properly followed bythe scientific community. In the publication procedure, theencouragement becomes the responsibility of single editorsand reviewers, and in practice it is extremely difficult to rulethat a description based on a single strain or very few strainsshould be rejected simply because of the small number ofstrains included, if the taxonomic characterization is wellInternational Journal of Systematic and Evolutionary Microbiology (2007), 57, 2185–2187 DOI 10.1099/ijs.0.64931-064931 G