Elucidation of genes involved in phototaxis of the cyanobacterium synechocystis sp. PCC 6803

Abstract

To identify the genes related with light signal transduction and gliding motility in cyanobacterial phototaxis, phototactic mutants were isolated using random and target mutagenesis and characterized by computerized motion analysis system in cyanobacterium Synechocystis sp. PCC 6803. Using UV mutagenesis, we initially isolated 5 types of phototactic mutants, such as negative, random, weak positive, weak negative and nonmotile mutants, based on phototactic gliding on the agar surface. We found negative and random mutants had a lesion(s) not in a photo-perception part but in an intracellular light signaling. Also one of the weak positive mutants did not have phototactic response only to far-red (730 nm) light. We suggest that these mutants can be used for identification of the genes related with light signal transduction and phototactic gliding motility. Also we performed random Tn5 mutations in Synechocystis sp. PCC 6803 in search for genes involved in phototactic gliding movement. One of the nongliding Tn5 mutant, S1-105, had an insertional inactivation in the slr1044 gene encoding a putative methyl-accepting chemotaxis protein. Interposon mutation on the slr1044 also eliminated gliding motility. This slr1044 was a part of a gene cluster (slr1041, slr1042, slr1043 and slr1044), which encodes proteins that have significant sequence similarity to chemotaxis proteins in enterics. So we renamed slr1044 ctr1 (cyanobacterial transducer). In the ctr1 interposon mutant, the expression of pilA1 was decreased 5-fold less than that of wild type, and also thick pili, that is believed to be motor for gliding, could not be observed by electron microscope. Therefore, we suggest that the Ctr1 protein function as a transducer that regulates the expression of pilA1, and thus is required for the biogenesis of thick pili. In addition, we found two additional gene clusters, which showed homology to chemotaxis proteins of enterics and Pil protein of the twitching bacterium P. ae...