Genomic structure of an economically important cyanobacterium, Arthrospira (Spirulina) platensis NIES-39

Abstract

An alkaliphilic halophilic cyanobacterium, Arthrospira (Spirulina), is an important organism for industrial applications and as a food supply. Almost the complete genome of A. platensis NIES-39 was determined in this study. The genome structure of A. platensis is estimated to be a single, circular chromosome of 6.8 Mbp, based on optical mapping. Annotation of this 6.7 Mbp sequence yielded 6630 protein-coding genes as well as 2 sets of rRNA genes and 40 tRNA genes. Of the protein-coding genes, 78% are similar to those of other organisms; the remaining 22% are currently unknown. A total 612 kbp of the genome comprises group II introns, phage-like sequences, insertion sequences and some repetitive elements. Genome rearrangement mediated by the phage-like sequences was detected. As A. platensis is the first genome for filamentous non-N₂-fixing cyanobacteria, filament-specific genes were highlighted by comparative genomic analysis. Further, we will report the unique characteristics of A. platensis genome especially about group I introns, restriction-modification systems, cAMP signal transduction systems and chemotaxis proteins.