All cyanobacterial species are dangerous (A time of new perspectives in cyanobacterial systematics)

Is it true that cyanobacterial taxonomy is a dangerous matter and that adequate tools to describe cyanobacterial species are still not available? We do not think so. We do not think this is the case for any type of living being. Besides being a "phylum", this large group of asexually reproducing microorganisms presents a large spectrum of phenotypic features such as morphology, life cycle, cell physiology and ultrastructure, biochemistry and genomic structure and a corresponding wide adaptive capability that can be readily used to recognize and differentiate species, all of which are being used in a progressively more integrated approach, the polyphasic approach. Moreover, for several cyanobacteria, a large amount of information on gene sequences is available or is rapidly becoming available for this approach. Nevertheless, what is still lacking is a satisfactory guideline for the definition of what a cyanobacterial species is in nature and what it shares with species of other types of living beings. The species concept in prokaryotes, and in particular in cyanobacteria is underdeveloped, meaning that few cyanobacteriologists, and only recently, have addressed the issue; and even among the few who have, there is no consensus on what a species is, or on whether it is possible and/or convenient at this time to try to describe species, or if we should bypass naming formal species for the time being and continue describing only genera with strain numbers. The lack of attention to formally developing one or more species concepts has had the practical consequence that very often no formal species concept is applied when new species are described and in most cases it is not made explicit. Yet there does seem to be consensus on arranging the groups described in phylogenetical order. The picture gets more complicated when the aim of adapting the classical cyanobacterial taxonomy to a phylogenetic framework is added. This derives in a paradox, since efforts are directed mostly to the genus level, but how to define or revise a genus, if no clear species concept or different ones have been used to define its own species? All considered, cyanobacteria seem to be an amenable model system for the definition of the species concept. We will present some examples and suggestions on how to link the theoretical development of the species concept for cyanobacteria to the experimental description of species.