Langmuir wave filamentation in the kinetic regime. I. Filamentation instability of Bernstein-Greene-Kruskal modes in multidimensional Vlasov simulations
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Signaling pathways can regulate biological responses by the transcriptional regulation of target genes. In yeast, multiple signaling pathways control filamentous growth, a morphogenetic response that occurs in many species including fungal pathogens. Here, we examine the role of signaling pathways that control filamentous growth in regulating adhesion-dependent surface responses, including mat formation and colony patterning. Expression profiling and mutant phenotype analysis showed that the major pathways that regulate filamentous growth [filamentous growth MAPK (fMAPK), RAS, retrograde (RTG), RIM101, RPD3, ELP, SNF1, and PHO85] also regulated mat formation and colony patterning. The chromatin remodeling complex, SAGA, also regulated these responses. We also show that the RAS and RTG pathways coregulated a common set of target genes, and that SAGA regulated target genes known to be controlled by the fMAPK, RAS, and RTG pathways. Analysis of surface growth-specific targets identified genes that respond to low oxygen, high temperature, and desiccation stresses. We also explore the question of why cells make adhesive contacts in colonies. Cell adhesion contacts mediated by the coregulated target and adhesion molecule, Flo11p , deterred entry into colonies by macroscopic predators and impacted colony temperature regulation. The identification of new regulators ( e.g. , SAGA), and targets of surface growth in yeast may provide insights into fungal pathogenesis in settings where surface growth and adhesion contributes to virulence.more » « less
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Collective behavior in spatially structured groups, or biofilms, is the norm among microbes in their natural environments. Though biofilm formation has been studied for decades, tracing the mechanistic and ecological links between individual cell morphologies and the emergent features of cell groups is still in its infancy. Here we use single-cell–resolution confocal microscopy to explore biofilms of the human pathogen Vibrio cholerae in conditions mimicking its marine habitat. Prior reports have noted the occurrence of cellular filamentation in V. cholerae , with variable propensity to filament among both toxigenic and nontoxigenic strains. Using a filamenting strain of V. cholerae O139, we show that cells with this morphotype gain a profound competitive advantage in colonizing and spreading on particles of chitin, the material many marine Vibrio species depend on for growth in seawater. Furthermore, filamentous cells can produce biofilms that are independent of primary secreted components of the V. cholerae biofilm matrix; instead, filamentous biofilm architectural strength appears to derive at least in part from the entangled mesh of cells themselves. The advantage gained by filamentous cells in early chitin colonization and growth is countered in long-term competition experiments with matrix-secreting V. cholerae variants, whose densely packed biofilm structures displace competitors from surfaces. Overall, our results reveal an alternative mode of biofilm architecture that is dependent on filamentous cell morphology and advantageous in environments with rapid chitin particle turnover. This insight provides an environmentally relevant example of how cell morphology can impact bacterial fitness.more » « less
