Required for swarm cell differentiation. Plays a crucial role in regulating the degree of cell flagellation. This protein is functional in undomesticated strains of B.subtilis but not in laboratory strains, such as 168, because of a frameshift mutation. Therefore laboratory strains of B.subtilis are unable to swarm. The frameshift in strain 168 is caused by a single insertion of an adenine in the codon for Tyr-12 which leads to the premature truncation of the protein in residue 13. In addition, the C-terminal section of swrAA was predicted to be an ORF (yvzD) by the genome project.