Novel putative photoreceptor and regulatory genes required for the positive phototactic movement of the unicellular motile cyanobacterium Synechocystis sp PCC 6803

Synechocystis sp, PCC 6803 is a unicellular motile cyanobacterium, which sh ows positive or negative phototaxis on agar plates under lateral illuminati on. By gene disruption in a substrain showing of positive phototaxis, it wa s demonstrated that mutants defective in sll0038, sll0039, sll0041, sll0042 or sll0043 lost positive phototaxis but showed negative phototaxis away fr om the light source. Mutants of sll0040, which is located within the cluste r of these genes, retained the capacity of positive phototaxis but to a les ser extent than the parent cells. These genes are homologous to che genes, which are involved in flagellar switching for bacterial chemotaxis, Interes tingly, sll0041 (designated pisJ1) is predicted to have a chromophore-bindi ng motif of phytochrome-like proteins and a signaling motif of chemorecepto rs for bacterial chemotaxis, It is strongly suggested that the positive pho totactic response was mediated by a phytochrome-like photoreceptor and CheA /CheY-type signal transduction system.