Gliding motility of a uranium tolerant Bacteroidetes bacterium Chryseobacterium sp. strain PMSZPI: Insights into the architecture of spreading colonies

Uranium tolerant soil bacterium Chryseobacterium sp. strain PMSZPI moved over solid agar surfaces by gliding motility thereby forming spreading colonies which is a hallmark of members of Bacteroidetes phylum. PMSZPI genome harbored orthologs of all the gld and spr genes considered as core bacteroidetes gliding motility genes of which gldK, gldL, gldM, and gldN were co-transcribed. Here, we present the intriguing interplay between gliding motility and cellular organization in PMSZPI spreading colonies. While nutrient deficiency enhanced colony spreading, high agar concentrations and presence of motility inhibitor like 5-hydroxyindole reduced the spreading. A detailed in situ structural analysis of spreading colonies revealed closely packed cells forming multiple layers at center of colony while the edges showed clusters of cells periodically arranged in hexagonal lattices interconnected with each other. The cell migration within the colony was visualized as branched structures wherein the cells were buried within extracellular matrix giving rise to fern like patterns. PMSZPI colonies exhibited strong iridescence that showed correlation with gliding motility. Presence of uranium reduced motility and iridescence and induced biofilm formation. This is a first report of gliding motility and iridescence in a bacterium from uranium enriched environment that could be of significant interest from an ecological perspective.

Disentangling cadherin-mediated cell-cell interactions in collective cancer cell migration

Cell dispersion from a confined area is fundamental in a number of biological processes, including cancer metastasis. To date, a quantitative understanding of the interplay of single cell motility, cell proliferation, and intercellular contacts remains elusive. In particular, the role of E- and N-Cadherin junctions, central components of intercellular contacts, is still controversial. Combining theoretical modeling with in vitro observations, we investigate the collective spreading behavior of colonies of human cancer cells (T24). Inhibition of E- and N-Cadherin junctions decreases colony spreading and average spreading velocities, without affecting the strength of correlations in spreading velocities of neighboring cells. Based on a biophysical simulation model for cell migration, we show that the behavioral changes upon disruption of these junctions can be explained by reduced repulsive excluded volume interactions between cells. This suggests that cadherin-based intercellular contacts sharpen cell boundaries leading to repulsive rather than cohesive interactions between cells, thereby promoting efficient cell spreading during collective migration.

Colony spreading of the gliding bacterium Flavobacterium johnsoniae in the absence of the motility adhesin SprB

Colony spreading of Flavobacterium johnsoniae is shown to include gliding motility using the cell surface adhesin SprB, and is drastically affected by agar and glucose concentrations. Wild-type (WT) and ΔsprB mutant cells formed nonspreading colonies on soft agar, but spreading dendritic colonies on soft agar containing glucose. In the presence of glucose, an initial cell growth-dependent phase was followed by a secondary SprB-independent, gliding motility-dependent phase. The branching pattern of a ΔsprB colony was less complex than the pattern formed by the WT. Mesoscopic and microstructural information was obtained by atmospheric scanning electron microscopy (ASEM) and transmission EM, respectively. In the growth-dependent phase of WT colonies, dendritic tips spread rapidly by the movement of individual cells. In the following SprB-independent phase, leading tips were extended outwards by the movement of dynamic windmill-like rolling centers, and the lipoproteins were expressed more abundantly. Dark spots in WT cells during the growth-dependent spreading phase were not observed in the SprB-independent phase. Various mutations showed that the lipoproteins and the motility machinery were necessary for SprB-independent spreading. Overall, SprB-independent colony spreading is influenced by the lipoproteins, some of which are involved in the gliding machinery, and medium conditions, which together determine the nutrient-seeking behavior.

Matrix production inBacillus subtilisbiofilms is localized to a propagating front

Bacterial biofilms are surface attached microbial communities encased in self-produced extracellular polymeric substances (EPS). Development of a mature biofilm must require coordinating cell differentiation and multicellular activity at scales much larger than the single microbial unit. Here we demonstrate that during development ofBacillus subtilisbiofilms, EPS matrix production is localized to a front propagating at the periphery. We show that within the front, cells switch off matrix production and transition to sporulation after a set time delay of∼100 min. Correlation analyses of fluctuations in fluorescence reporter activity reveals that the front emerges from a pair of gene expression waves of matrix production and sporulation. The expression waves travel across cells that are immobilized in the biofilm matrix, in contrast to active cell migration or horizontal colony spreading. A single length scale and time scale couples the spatiotemporal propagation of both fronts throughout development, with the front displacement obeying at1/2scaling law. As a result, gene expression patterns within the advancing fronts collapse to self-similar expression profiles. Our results indicate that development of bacterial biofilms may be governed by universal wave-like dynamics localized to a self-similar front.

Evolutionary plasticity of AmrZ regulation in Pseudomonas

amrZ, a master regulator protein conserved across Pseudomonads, can be either a positive or negative regulator of swimming motility depending on the species examined. To better understand plasticity in the regulatory function of AmrZ, we characterized the mode of regulation for this protein for two different motility related phenotypes in P. stutzeri. As in P. syringae, AmrZ functions as a positive regulator of swimming motility within P. stutzeri, which suggests that the functions of this protein with regards to swimming motility have switched at least twice across Pseudomonads. Shifts in mode of regulation cannot be explained by changes in AmrZ sequence alone. We further show that AmrZ acts as a positive regulator of colony spreading within this strain, and that this regulation is at least partially independent of swimming motility. Closer investigation of mechanistic shifts in dual function regulators like AmrZ could provide unique insights into how transcriptional pathways are rewired between closely related species.

Evolutionary plasticity of AmrZ regulation in Pseudomonas

amrZ, a master regulator protein conserved across Pseudomonads, can be either a positive or negative regulator of swimming motility depending on the species examined. To better understand plasticity in the regulatory function of AmrZ, we characterized the mode of regulation for this protein for two different motility related phenotypes in P. stutzeri. As in P. syringae, AmrZ functions as a positive regulator of swimming motility within P. stutzeri, which suggests that the functions of this protein with regards to swimming motility have switched at least twice across Pseudomonads. Shifts in mode of regulation cannot be explained by changes in AmrZ sequence alone. We further show that AmrZ acts as a positive regulator of colony spreading within this strain, and that this regulation is at least partially independent of swimming motility. Closer investigation of mechanistic shifts in dual function regulators like AmrZ could provide unique insights into how transcriptional pathways are rewired between closely related species.