Arthrospira (Spirulina): Systematics and EcophysioIogy

Abstract

Notwithstanding the official recognition in 1989 of the cyanobacteria Arthrospiru and Spirulina as distinct genera. the term “Spirulina”has been used to indicate the species of both genera indifferently. particularly the species “S. platensis” and “S. maxima” cultivated and sold as food. feed and a specialty product source.The successful commercial exploitation of Arthrospira, because of its high nutritional value. chemical composition and the safety of its biomass, has made it one of the most important industrially cultivated microalgae. This chapter describes the ecology of Arthrospira, together with morphological and ultrastructural features relevant for supporting the systematic position of this organism. While the confused taxonomy of Arthrospira and its relationship with Spirulina have been resolved by 16S rRNA sequence analysis, the long debated problem of species definition is still ongoing. One study of ten strains suggested that the morphological criteria used to identify the species (A. maxima, A. platensis) corresponded to the molecular data obtained by total DNA restriction profile analyses. However, another study based on a wider range of classical species and forty different strains failed to show a clear correspondance with molecular data obtained for one part of the genome. This emphasises the need to address the problem of the definition of a species by using a polyphasic approach. Knowledge of the ecophysiology of Arthrospira, essential for understanding the growth requirements of this alkaliphilic organism in the natural environment, has been used in developing suitable technologies for mass cultivation. The relationships between environmental and cultural factors, which govern productivity in outdoor cultures, are discussed in connection with growth yield and efficiency. The response of Arthrospira and its modification under stress are described, together with the strategy of osmotic adjustment and the mechanism of internal pH regulation to alkalinity. The metabolic plasticity of the response of this cyanobacterium to disparate environmental stimuli is demonstrated in the natural environment, but is also well-expressed in the maintenance of highly productive monoculture in intensive outdoor cultivation systems.