Identification of genes required for swarming motility in Bacillus subtilis using transposon mutagenesis and high-throughput sequencing (TnSeq)

Abstract

Bacillus subtilis exhibits swarming motility, a flagellar-mediated form of surface motility. Here we use high-throughput transposon mutagenesis and sequencing (TnSeq) to identify candidate genes required for swarming. The TnSeq approach identified all of the known genes required for flagellar biosynthesis as well as nearly all of the previously reported regulators that promote swarming. Moreover, we identified an additional 36 genes that improve swarming and validated them individually. Among these, two mutants with severe defects were recovered including fliT, required for flagellar biosynthesis, and a gene of unknown function yolB, whose defect could not be attributed to a lack of flagella. Our work indicates that TnSeq is a powerful approach for the identification of genes required for motility that drives outward expansion of a colony on plates. IMPORTANCEIn TnSeq, transposons are randomly inserted throughout the chromosome at a population level, but insertions that disrupt genes of essential function cause strains that carry them to fall out of the population and appear under-represented at the sequence level. Here we apply TnSeq to the non-essential phenotype of motility in B. subtilis and spatially select for cells proficient in swarming. We find that insertions in nearly all genes previously identified as required for swarming are under-represented in TnSeq analysis, and we identify 36 additional genes that enhance swarming. We suggest that TnSeq is a powerful tool for the genetic analysis of motility and likely other non-lethal screens for which enrichment is strong.