Analysis ofBrevundimonas subvibrioidesdevelopmental signaling systems reveals unexpected differences between phenotypes and c-di-GMP levels

Abstract

AbstractThe DivJ-DivK-PleC signaling system ofCaulobacter crescentusis a signaling network that regulates polar development and the cell cycle. This system is conserved in related bacteria, including the sister genusBrevundimonas. Previous studies had shown unexpected phenotypic differences between theC. crescentus divKmutant and the analogous mutant ofBrevundimonas subvibrioides, but further characterization was not performed. Here, phenotypic assays analyzing motility, adhesion, and pilus production (the latter characterized by a newly discovered bacteriophage) revealed thatdivJandpleCmutants have mostly similar phenotypes as theirC. crescentushomologs, butdivKmutants maintain largely opposite phenotypes than expected. Suppressor mutations of theB. subvibrioides divKmotility defect were involved in cyclic-di-GMP (c-di-GMP) signaling, including the diguanylate cyclasedgcB, andcleDwhich is hypothesized to affect flagellar function in a c-di-GMP dependent fashion. However, the screen did not identify the diguanylate cyclasepleD.Disruption ofpleDinB. subvibrioidescaused hypermotility in wild-type, but not in thedivKbackground. Analysis of c-di-GMP levels in these strains revealed incongruities between c-di-GMP levels and displayed phenotypes with a notable result that suppressor mutations altered phenotypes but had little impact on c-di-GMP levels in thedivKbackground. Conversely, when c-di-GMP levels were artificially manipulated, alterations of c-di-GMP levels in thedivKstrain had minimal impact on phenotypes. These results suggest that DivK performs a critical function in the integration of c-di-GMP signaling into theB. subvibrioidescell cycle.ImportanceCyclic-di-GMP signaling is one of the most broadly conserved signaling systems in bacteria, but there is little understanding of how this system directly affects the physiology of the organism. InC. crescentus, c-di-GMP has been integrated into the developmental cell cycle, but there is increasing evidence that environmental factors can impact this system as well. The research presented here suggests that developmental signaling could impact physiological Processes in c-di-GMP dependent and independent ways. This hints that the integration of these signaling networks could be more complex than previously hypothesized, which could have a bearing on the larger field of c-di-GMP signaling. In addition, this work further examines how much models developed in one organism can be extrapolated to related organisms.