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 less 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 broad effect on global 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 flagella gene components affect not only motility but can also have considerable and unexpected consequences on other aspects of cell biology. Overall design: Gene expression of two different Caulobacter crescentus NA1000 mutants were compared to wildtype controls; all experiments were carried out in triplicate