Flagellar mutants have reduced pilus synthesis in Caulobacter crescentus

Surface appendages such as flagella and type IV pili mediate a broad range of bacterial behaviors including motility, attachment, and surface sensing. While many species harbor both flagella and type IV pili, little is known about how or if their synthesis is coupled. Here, we show that deletions of genes encoding different flagellum machinery components result in a reduction of pilus synthesis in Caulobacter crescentus . First, we show that different flagellar mutants exhibit different levels of sensitivity to a pilus-dependent phage and that fewer cells within populations of flagellar mutants make pili. Furthermore, we find that single cells within flagellar mutant populations produce less pili per cell. We demonstrate that these gene deletions result in reduced transcription of pilus-associated genes and have a slight, but significant effect on general transcription profiles. Finally, we show that the decrease in pilus production is due to a reduction in the pool of pilin subunits that are polymerized into pilus fibers. These data demonstrate that mutations in flagellar gene components affect not only motility but can also have considerable and unexpected consequences on other aspects of cell biology. IMPORTANCE Most bacterial species synthesize surface-exposed appendages that are important for environmental interactions and survival under diverse conditions. It is often assumed that these appendages act independently of each other and that mutations in either system can be used to assess functionality in specific processes. However, we show that mutations in flagellar genes can impact the production of type IV pili as well as alter general RNA transcriptional profiles when compared to a wildtype strain. These data demonstrate that seemingly simple mutations can broadly affect cell regulatory networks.