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

A filamentous non-N(2)-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 Ca(2+)-binding proteins and in chemotaxis proteins. Filament-specific genes were highlighted by comparative genomic analysis.

Changes in the amount of cellular trehalose, the activity of maltooligosyl trehalose hydrolase, and the expression of its gene in response to salt stress in the cyanobacterium spirulina platensis.

The amount of trehalose in cells of the cyanobacterium Spirulina (Arthrospira) platensis increased rapidly when a high concentration of NaCl was added to the culture medium. Inhibition of sodium ion transport by amiloride and monensin significantly decreased the amount of cellular trehalose, suggesting that the influx of sodium ions into the cells is coupled with the accumulation of trehalose. The amount of maltooligosyl trehalose hydrolase (Mth) which produces trehalose from maltooligosyl trehalose increased gradually after the increase in cellular trehalose. The gene for Mth was cloned and identified by Southern blot analysis. Real time RT-PCR analysis revealed that the expression of mth was enhanced by the addition of NaCl to the culture medium. It was concluded that both catalytic activity of Mth and the synthesis of Mth protein were enhanced by the addition of NaCl to the cells.

The role of a gene cluster for trehalose metabolism in dehydration tolerance of the filamentous cyanobacterium Anabaena sp. PCC 7120.

Expression of the genes for trehalose synthesis (mts and mth, encoding maltooligosyl trehalose synthase and hydrolase) and trehalose hydrolysis (treH) in Anabaena sp. PCC 7120 was up-regulated markedly upon dehydration. However, the amount of trehalose accumulated during dehydration was small, whereas a large amount of sucrose was accumulated. Northern blotting analysis revealed that these genes were transcribed as an operon. Gene disruption of mth resulted in a decrease in the trehalose level and in tolerance during dehydration. In contrast, gene disruption of treH resulted in an increase in both the amount of trehalose and tolerance. These results suggest that trehalose is important for the dehydration tolerance of this cyanobacterium. The amount of trehalose accumulated during dehydration was small, corresponding to 0.05-0.1 % of dry weight, suggesting that trehalose did not stabilize proteins and membranes directly during dehydration. To reveal the role of trehalose, the expression profiles of the wild-type strain and gene disruptants during dehydration were compared by using oligomeric DNA microarray. It was found that the expression of two genes, one of which encodes a cofactor of a chaperone DnaK, correlated with trehalose content, suggesting that a chaperone system induced by trehalose is important for the dehydration tolerance of Anabaena sp. PCC 7120.