2007, SwmB, a 1.12megadalton protein that is required for nonflagellar swimming motility in Synechococcus

SwmB is required for swimming motility in Synechococcus sp. strain WH8102. This highly repetitive 1.12-MDa polypeptide is associated with the cell surface, where it is arranged in a punctate manner. Inactivation of swmB does not affect the localization of SwmA, an S-layer protein also required for swimming. A monophyletic clade of marine Synechococcus (17) exhibits a novel type of motility. These cells are able to swim through their liquid environment in the absence of flagella or any other readily visible organelle (5, 19). While the mechanism of non-flagellar swimming motility in Synechococcus is still not under-stood, three chromosomal regions containing genes required for motility were identified by transposon mutagenesis of Syn-echococcus sp. strain WH8102 (13). One of these regions in-cludes an exceptionally large and repetitive open reading frame (ORF), swmB, insertions in which eliminate motility. Here we show that this large ORF is expressed and its product is localized to the cell surface. Furthermore, we show that th