Kazuko Ohmori

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

A filamentous non-N2-fixing cyanobacterium, Arthrospira (Spirulina) platensis, 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 Mb, based on optical mapping. Annotation of this 6.7 Mb sequence yielded 6630 protein-coding genes as well as two 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 kb of the genome comprise group II introns, insertion sequences and some repetitive elements. Group I introns are located in a protein-coding region. Abundant restriction-modification systems were determined. Unique features in the gene composition were noted, particularly in a large number of genes for adenylate cyclase and haemolysin-like Ca2+-binding proteins and in chemotaxis proteins. Filament-specific genes were highlighted by comparative genomic analysis.

Rapid change in cyclic 3′,5′-AMP concentration triggered by a light-off or light-on signal in Anabaena cylindrica

In a nitrogen-fixing cyanobacterium, Anabaena cylindrica, an immediate light-to-dark transition caused an increase in cAMP concentration within 1 min. Conversely, a dark-to-light transition caused a rapid fall in cellular cAMP concentration. The concentration of cyclic 3′5′-GMP(cGMP) was several times lower than that of cAMP and was not largely affected by a light-off or light-on signal.