The histidine kinase Hik33 perceives osmotic stress and cold stress in Synechocystis sp PCC 6803.

The stress imposed on living organisms by hyperosmotic conditions and low temperature appears to be perceived via changes in the physical state of membrane lipids. We compared genome-wide patterns of transcription between wild-type Synechocystis sp. PCC 6803 and cells with a mutation in the histidine kinase Hik33 using a DNA microarray. Our results indicated that Hik33 regulated the expression of both osmostress-inducible and cold-inducible genes. The respective genes that were regulated by Hik33 under hyperosmotic and low-temperature conditions were, for the most part, different from one another. However, Hik33 also regulated the expression of a set of genes whose expression was induced both by osmotic stress and by cold stress. These results indicate that Hik33 is involved in responses to osmotic stress and low-temperature stress but that the mechanisms of the responses differ.