Proteome analysis at the subcellular level of the cyanobacterium Spirulina platensis in response to low-temperature stress conditions.

The present study addresses the differential expression of Spirulina platensis proteins detected during cold-induced stress, analyzed at the subcellular level. In performing differential expression analysis, the results revealed upregulated proteins in every subcellular fraction, including two-component response systems, DNA repair, molecular chaperones, stress-induced proteins and proteins involved in other biological processes such as secretion systems and nitrogen assimilation. The chlorophyll biosynthetic proteins, protochlorophyllide oxidoreductase and ChlI, had unique expression patterns as detected in the thylakoid membrane; the levels of these proteins immediately decreased during the first 45 min of low-temperature exposure. In contrast, their expression levels significantly increased after low-temperature exposure, indicating the relevance of the chlorophyll biosynthesis in Spirulina in response to low-temperature stress in the light condition. In addition, this is the first report in which genome-based protein identification in S. platensis by peptide mass fingerprinting was performed using the database derived from the unpublished Spirulina genome sequence.