pilG gene cluster and split pilL genes involved in pilus biogenesis, motility and genetic transformation in the cyanobacterium Synechocystis sp PCC 6803

The unicellular motile cyanobacterium Synechocystis sp. PCC 6803 exhibits phototactic motility that depends on the type 1 like thick pilus structure. By gene disruption analysis, we showed that a gene cluster of slr1041, slr1042, slr1043 and slr1044, whose predicted products are homologous to PatA, CheY, CheW and MCP, respectively, was more or less required for pilus assembly, motility and natural transformation competency with extraneous DNA. By sequence homology, the missing cheA-like gene in this cluster was identified as novel split genes, slr0073 and slr0322, at separate loci on the genome. This was confirmed by nonmotile phenotype of their disruptants. Unique hyperpiliation was observed in the slr1042 and slr0073 disruptants, suggestive of their specific interaction with pilT1. The genes, thus identified as pil genes in this study, were designated piIG (slr1041), pilH (slr1042), pill (slr1043), pilJ (slr1044), pilL-N (slr0073) and pilL-C (slr0322).