Biology subjects

Polin, M.

Publications and source records attributed to Polin, M..

6 recordsLinked to original sources

bioRxiv2025

Trypanosomes Modulation of Motility from Swimming to Threading Propulsion in Confined Environments

Trypanosoma brucei (T. brucei) is a protozoan parasite that lives extracellularly in the body fluids of its hosts. In mammals, these environments include the vascular system and the interstitial spaces of various organs, such as the skin and adipose tissue. How the parasite disseminates within the host remains largely unresolved. It is clear however, that parasite motility plays a central role. The unicellular, eukaryotic flagellate is a versatile microswimmer, like bacteria or sperm cells, albeit structurally far more complex than these classical model systems. In addition to possessing a flagellum attached alongside a strongly polarised cell body, the parasite is capable of swimming both forwards and backwards. The trypanosome must be capable of navigating effectively even under extreme physical and mechanical constraints. It can do so in the mammalian host with only one main morphotype. This means that the cell is mechanically adapted to motion in diverse challenging microenvironments. To address how, we study the parasites in different viscoelastic regimes up to conditions mimicking tissue confinement. Next to quantitative high speed video microscopy, we employ digital holography microscopy, yielding three-dimensional subcellular resolution. We detail the mechanical reaction of the flexible cell body with its uniquely attached flagellum to increasing confinement and show how the trypanosomes are able to maintain their motile capabilities to spread in dense tissue.

microbiology↗

bioRxiv2024

Cellular (de)coordination in gliding motility and plectoneme formation

2Cyanobacteria are key contributors to biogeochemical cycles through photosynthesis and carbon fixation. In filamentous, multicellular cyanobacteria these functions can be influenced through gliding motility, which enables filaments to localise in response to light and also form aggregates. Here, we use the aggregate forming species Fluctiforma draycotensis to study gliding motility dynamics in detail. We find that filaments move in curved and straight trajectories interspersed with re-orientation or reversal of direction. Most reversals take few seconds but some take substantially longer, resulting in a long-tailed distribution of stoppage times. Mean filament speeds range around a micron per second with a relatively uniform distribution against filament length, implying that all or fixed proportion of cells in a filament contribute to movement. We implement a biophysical model that can recapitulate these findings. Model simulations show that for filaments to reverse quickly, cells in a filament must achieve high coordination of the direction of the forces that they generate. To seek experimental support of this prediction, we track individual cells in a filament. This reveals that cells translational movement is fully coupled with their rotation along the long-axis of the filament, and that cellular movement remains coordinated throughout a reversal. For some filaments, especially longer ones, however, we also find that cellular coordination can be lost, and filaments can form buckles that can twist around themselves, resulting in plectonemes. The experimental findings and the biophysical model presented here will inform future studies of individual and collective filament movement. 1 Significance StatementCyanobacteria contribute to global oxygen production and carbon capture. Some cyanobacteria exist as multicellular filaments and display gliding motility that allows them to respond to light and to form aggregates, which influences their biological functions. Here, we study the dynamics of gliding motility. We find that filaments movement is interspersed with re-orientation or reversal of direction and that mean filament speed is mostly independent of filament length. We implement a biophysical model that predicts these features to relate to cells in a filament having high coordination of the direction of the forces that they generate. We find experimental support for this predicted cellular coordination, but also discover instances of longer filaments loosing coordination, resulting in buckling and entangling with other filaments.

biophysics↗

bioRxiv2023

Emergence of synchronised growth oscillations in filamentous fungi

Soil fungi are important decomposers of organic matter and play crucial roles in the biogeochemical cycles in the soil. Many species of fungi grow in the form of branched networks. While there have been investigations on the growth and architecture of the fungal networks, their growth dynamics in space and time is still not fully understood. In this study, we monitor the growth dynamics of the plant-promoting filamentous fungus Serendipita indica for several days in a controlled environment within a microfluidic channel. We find that this species displays synchronized growth oscillations with the onset of sporulation and at a period of 3 hours. Quantifying this experimental synchronisation of oscillatory dynamics, we show that the synchronisation can be captured by the nearest neighbour Kuramoto model. Our analysis suggested the existence of millimetre-scale cell-cell communication across the fungi network. The microfluidic setup presented in this work may aid the future characterization of the molecular mechanisms of the cell-cell communication, which could in turn be exploited in order to control fungi growth and reproductive sporulation in soil and plant health management.

biophysics↗

bioRxiv2020

Swarming bacteria undergo localized dynamic phase transition to form stress-induced biofilms

Self-organized multi-cellular behaviors enable cells to adapt and tolerate stressors to a greater degree than isolated cells. However, whether and how cellular communities alter their collective behaviors adaptively upon exposure to stress is largely unclear. Here we address this question using Bacillus subtilis, a model system for bacterial multicellularity. We discover that, upon exposure to a spatial gradient of kanamycin, swarming bacteria activate matrix genes and transit to biofilms. The initial stage of this transition is underpinned by a stress-induced multi-layer formation, emerging from a biophysical mechanism reminiscent to motility-induced phase separation (MIPS). The physical nature of the process suggests that stressors which suppress the expansion of swarms would induce biofilm formation. Indeed, a simple physical barrier also induces a swarm-to-biofilm transition. Based on the gained insight, we propose a promising strategy of antibiotic treatment to effectively inhibit the transition from swarms to biofilms by targeting the localized phase transition.

biophysics↗

bioRxiv2019

Phototaxis of the dominant marine pico-eukaryote Micromonas sp.: from population to single cell

Micromonas commoda (previously Micromonas pusilla, a unicellular photosynthetic picoeukaryote globally dominant in marine ecosystems, has previously been qualified as being strongly phototactic. To date, no detailed quantitative or qualitative description of this behaviour has been reported, nor have thorough studies of its motility been undertaken. This primary producer has only been qualitatively described as utilizing run-and-tumble motion, but such motility strategy is incompatible with its morphology comprising only one propelling flagellum. Moreover, it is still unclear as to how Micromonas sp. detects a light direction due to the lack of a dedicated eyespot; the organism is essentially blind. Here we first perform population-scale phototactic experiments to show that this organism actively responds to a wide range of light wavelengths and intensities. These population responses are well accounted for within a simple drift-diffusion framework. Based on single-cell tracking experiments, we then detail thoroughly Micromonas sp.s motility which resembles run-and-reverse styles of motion commonly observed in marine prokaryotes and that we name stop-run or reverse. The associated peculiar microscopic changes upon photo-stimulation are finally described and integrating those into jump-diffusion simulations appears to produce phototactic drifts that are quantitatively compatible with those obtained experimentally at the population level.

biophysics↗

bioRxiv2019

Cell explosions: single cell death triggers an avoidance response in local populations of the ecologically prominent phytoplankton genus Micromonas

The global phytoplankton community, comprised of aquatic photosynthetic organisms, is acknowledged for being responsible for half of the global oxygen production Prominent among these is the pico-eukaryote Micromonas commoda (formally Micromonas pusilla of the genus Micromonas), which can be found in marine and coastal environments across the globe. Cell death of phytoplankton has been identified as contributing to the largest carbon transfers on the planet moving 109 tonnes of carbon in the oceans every day. During a cell death organic matter is released into the local environment which can act as both a food source and a warning signal for nearby organisms. Here we present a novel motility response to single cell death in populations of Micromonas sp., where the death of a single cell releases a chemical patch triggers surrounding cells to escape the immediate affected area. These so-called "burst events" are then modelled and compared with a spherically symmetric diffusing patch which is found to faithfully reproduce the observed behaviour. Finally, laser ablation of single cells reproduces the observed avoidance response, confirming that Micromonas sp. has evolved a specific motility response in order to escape harmful environments for example nearby predator-prey interactions or virus lysis induced cell death.

biophysics↗