CIRCADIAN-RHYTHM OF THE CYANOBACTERIUM SYNECHOCYSTIS SP STRAIN PCC-6803 IN THE DARK

The cyanobacterium Synechocystis sp. strain PCC 6803 exhibited circadi an rhythms in complete darkness, To monitor a circadian rhythm of the Synechocystis cells in darkness, we introduced a P-dnaK1::luxAB gene f usion (S, Aoki, T, Kondo, and M. Ishiura, J. Bacteriol, 177:5606-5611, 1995), which was composed of a promoter region of the Synechocystis d naK1 gene and a promoterless bacterial luciferase luxAB gene set, as a reporter into the chromosome of a dark-adapted Synechocystis strain. The resulting dnaK1-reporting strain showed bioluminescence rhythms wi th a period of 25 h (on agar medium supplemented with 5 mM glucose) fo r at least 7 days in darkness. The rhythms were reset by 12-h-light-12 -h-dark cycles, and the period of the rhythms was temperature compensa ted for between 24 and 31 degrees C. These results indicate that light is not necessary for the oscillation of the circadian clock in Synech ocystis.