Impact of flagellar filament length on Campylobacter jejuni for colonization and flagellar-dependent phenotypes

Many bacteria produce flagella to swim and navigate through environments. Depending on the species, flagella are beneficial for other activities such as sensing surfaces to initiate biofilm development, secretion of specific proteins, and interactions with hosts to promote colonization or pathogenesis of disease. The extracellular region of the flagellum consists mostly of the filament, which is required for many flagellar-dependent activities. The length of the filament varies across bacterial flagellates and even stochastically within a clonal population, but it is unknown whether or how altering filament length impacts flagellar function for motility and other activities. We recently discovered a mechanism by which FlaG of Campylobacter jejuni and other polarly flagellated bacteria controls flagellar filament length so that these species produce shorter filaments than their peritrichous counterparts. We exploited a set of isogenic C. jejuni mutants producing significantly longer and shorter flagellar filaments than WT to assess the impact of filament length on activities of C. jejuni necessary for commensal colonization of a natural host. We found that production of shorter flagellar filaments slows swimming velocity and hinders intestinal colonization of chickens. Although production of shorter and longer flagellar filaments differently impacted cellular autoagglutination, only a subtle impact on biofilm formation was observed. We also acquired evidence that FlaG itself may impact biofilm development, suggesting that FlaG may have another function besides controlling flagellar filament length. Overall, our data suggest that shortening flagellar filaments has a greater impact on flagellar-dependent activities of C. jejuni than producing overly elongated filaments.

Flagella and flagellar motility are important to propel many bacteria through environments, biofilm formation, and infection of respective hosts. Most often, the importance of flagella for a species has been assessed with mutants lacking flagella altogether or only the extracellular filament while retaining the basal body. We addressed whether altering filament length impacts flagellar-dependent activities for host colonization. We exploited isogenic Campylobacter jejuni mutants that synthesize longer and shorter filaments on average relative to WT to find that production of shorter filaments had greater negative impacts on motility, autoagglutination, and commensal colonization compared to bacteria that produce elongated filaments. Our findings suggest that polar flagellates may produce a flagellar filament of minimal length to achieve flagellar functions and preserve fitness.