Photomovement of the gliding cyanobacterium Synechocystis sp PCC 6803

Using a computerized videomicroscope motion analysis system, we investigate d the photomovements of two Synechocystis sp, (PCC 6803 and ATCC 27184), Sy nechocystis sp, PCC 6803 displays a relatively slow gliding motion. The pho totactic and photokinetic speeds of this cyanobacterium in liquid media wer e 5 mu m/min and 15.8 mu m/min, respectively, at 3 mu mol/m(2)/s of stimula nt white light. Synechocystis sp, PCC 6803 senses light direction rather th an intensity for phototaxis, Synechocystis sp, ATCC 27184 showed a weak pho tokinesis but no phototaxis, Analysis of Synechocystis sp, ATCC 27184 sugge sts that the loss of phototaxis results from spontaneous mutation during se veral years of subculture. When directional irradiation was applied, the ce ll population of Synechocystis sp, PCC 6803 began to deviate from random mo vement and reached maximum orientation at 5 min after the onset of stimulan t white light. Synechocystis sp, PCC 6803 showed high sensitivity to the st imulant white light of fluence rates as low as 0.002 mu mol/m(2)/s. Neither 1,3-dichlorophenyldimethyl urea nor cyanide affected phototactic orientati on, whereas cyanide inhibited gliding speed. This result suggests that the phototaxis of Synechocystis sp, PCC 6803 is independent of photosynthetic p hosphorylation and that its gliding movement is primarily powered by oxidat ive phosphorylation, In the visible wavelength region, 560 nm, 660 nm and e ven 760 nm caused positive phototaxis, However, 360 nm light induced striki ngly negative phototaxis, Therefore, at least two independent photoreceptor s may exist to control phototaxis, The photoreceptor for positive phototaxi s appears likely to be a phytochrome-like tetrapyrrole rather than chloroph yll a.