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The downregulation of Pseudomonas aeruginosa flagellar motility is a key event in biofilm formation, host-colonization, and the formation of microbial communities, but the external factors that repress motility are not well understood. Here, we report that under swarming conditions, swarming motility can be repressed by cells that are non-motile due to the absence of a flagellum or flagellar rotation. Non-swarming cells, due to mutations that prevent either flagellum biosynthesis or rotation, present at 5% of the total population suppressed swarming of wild-type cells under the conditions tested in this study. Non-swarming cells required functional type IV pili and the ability to produce Pel exopolysaccharide to suppress swarming by the flagellated wild type. In contrast, flagellated cells required only type IV pili, but not Pel production, in order for swarming to be repressed by non-flagellated cells. We hypothesize that interactions between motile and non-motile cells may enhance the formation of sessile communities including those involving multiple genotypes, phenotypically-diverse cells, and perhaps other species.ImportanceOur study shows that, under the conditions tested, a small population of non-swarming cells can impact the motility behavior of the larger population. The interactions that lead to the suppression of swarming motility require type IV pili and a secreted polysaccharide, two factors with known roles in biofilm formation. These data suggest that interactions between motile and non-motile cells may enhance the transition to sessile growth in populations and promote interactions between cells with different genotypes.

During replication of herpesviruses, capsids escape from the nucleus into the cytoplasm by budding at the inner nuclear membrane. This unusual process is mediated by the viral nuclear egress complex (NEC) that deforms the membrane around the capsid by oligomerizing into a hexagonal, membrane-bound scaffold. Here, we found that highly basic membrane-proximal regions (MPRs) of the NEC alter lipid order by inserting into the lipid headgroups and also promote negative Gaussian curvature. We also find that the electrostatic interactions between the MPRs and the membranes are essential for membrane deformation. One of the MPRs is phosphorylated by a viral kinase during infection, and the corresponding phosphomimicking mutations block capsid nuclear egress. We show that the same phosphomimicking mutations disrupt the NEC/membrane interactions and inhibit NEC-mediated buddingin vitro, providing a biophysical explanation for thein-vivophenomenon. Our data suggest that the NEC generates negative membrane curvature by both lipid ordering and protein scaffolding and that phosphorylation acts as an “off” switch that inhibits the membrane-budding activity of the NEC to prevent capsid-less budding.

Despite possessing the machinery to sense, adhere to, and proliferate on surfaces, it is commonly observed that bacteria initially have a difficult time attaching to a surface. Before forming a bacterial biofilm, planktonic bacteria exhibit a random period of transient surface attachment known as “reversible attachment” which is poorly understood. Using community tracking methods at single-cell resolution, we examine how reversible attachment progresses during initial stages of surface sensing.Pseudomonas aeruginosastrains PAO1 and PA14, which exhibit similar exponential trends of surface cell population increase, show unanticipated differences when the behavior of each cell was considered at the full lineage level and interpreted using the unifying quantitative framework of an exactly solvable stochastic model. Reversible attachment comprises two regimes of behavior, processive and nonprocessive, corresponding to whether cells of the lineage stay on the surface long enough to divide, or not, before detaching. Stark differences between PAO1 and PA14 in the processive regime of reversible attachment suggest the existence of two complementary surface colonization strategies, which are roughly analogous to “immediate-” vs “deferred-gratification” in a prototypical cognitive-affective processing system. PAO1 lineages commit relatively quickly to a surface compared to PA14 lineages. PA14 lineages allow detaching cells to retain memory of the surface so that they are primed for improved subsequent surface attachment. In fact, it is possible to identify motility suppression events in PA14 lineages in the process of surface commitment. We hypothesize that these contrasting strategies are rooted in downstream differences between Wsp-based and Pil-Chp-based surface sensing systems.

Pacemaker neurons exert control over neuronal circuit function by their intrinsic ability to generate rhythmic bursts of action potential. Recent work has identified rhythmic gut contractions in human, mice and hydra to be dependent on both neurons and the resident microbiota. However, little is known about the evolutionary origin of these neurons and their interaction with microbes. In this study, we identified and functionally characterized prototypical ANO/SCN/TRPM ion channel expressing pacemaker cells in the basal metazoanHydraby using a combination of single-cell transcriptomics, immunochemistry, and functional experiments. Unexpectedly, these prototypical pacemaker neurons express a rich set of immune-related genes mediating their interaction with the microbial environment. Functional experiments validated a model of the evolutionary emergence of pacemaker cells as neurons using components of innate immunity to interact with the microbial environment and ion channels to generate rhythmic contractions.

The second messenger signaling molecule cyclic diguanylate monophosphate (c-di-GMP) drives the transition from planktonic to biofilm growth in many bacterial species.Pseudomonas aeruginosahas two surface sensing systems that produce c-di-GMP in response to surface adherence. The current thinking in the field is that once cells attach to a surface, they uniformly respond with elevated c-di-GMP. Here, we describe how the Wsp system generates heterogeneity in surface sensing, resulting in two physiologically distinct subpopulations of cells. One subpopulation has elevated c-di-GMP and produces biofilm matrix, serving as the founders of initial microcolonies. The other subpopulation has low c-di-GMP and engages in surface motility, allowing for exploration of the surface. We also show that this heterogeneity strongly correlates to surface behavior for descendent cells. Together, our results suggest that after surface attachment,P. aeruginosaengages in a division of labor that persists across generations, accelerating early biofilm formation and surface exploration.