Biology subjects

Cremin, K.

Publications and source records attributed to Cremin, K..

5 recordsLinked to original sources

bioRxiv2026

Emergent particle collection by cyanobacteria through gliding motility and filament buckling

Cyanobacterial macrostructures such as mats, aggregates, and stromatolites are observed in diverse habitats. These structures incorporate organic and inorganic matter and form microenvironments enabling biochemical transformations. Macrostructures are found to be associated with motile, filamentous cyanobacteria, but to what extent, and how filament motility can drive macrostructure formation is unclear. To address this question, we study macrostructure formation in a well-characterised freshwater cyanobacterial community dominated by the filamentous cyanobacterium Fluctiforma draycotensis. We discover an emergent particle collection behaviour that results in aggregate macrostructures composed of a solid core surrounded by an outer layer dominated by entangled cyanobacterial filaments. We show that the particle collection and subsequent aggregate formation result from the gliding motility of the cyanobacteria. Developing a novel 3D model of active filament movement, we analyse how filament morphology and mechanical properties affect movement dynamics, particle collection, and filament entanglement. We predict that particle collection requires filaments above a certain length and flexibility. We confirm the resulting prediction of length dependence of particle collection behavior with shortened filaments of F. draycotensis and naturally short Pseudanabaena sp. filaments. Together, our results show that filamentous cyanobacteria can use gliding motility to actively engineer their environments through particle collection and macrostructure formation, and that this ability is confined to a part of the filament phase space in terms of length and flexibility. These insights will allow better prediction of macrostructure formation in natural habitats and specific cyanobacterial species, and the engineering of cyanobacterial macrostructures for biotechnological applications.

biophysics↗

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

Can Single Cell Respiration be Measured by Scanning Electrochemical Microscopy (SECM)?

Ultramicroelectrode (UME), or - equivalently - microelectrode, probes are increasingly used for single-cell measurements of cellular properties and processes, including physiological activity, such as metabolic fluxes and respiration rates. Major challenges for the sensitivity of such measurements include: (i) the relative magnitude of cellular and UME fluxes (manifested in the current); and (ii) issues around the stability of the UME response over time. To explore the extent to which these factors impact the precision of electrochemical cellular measurements, we undertake a systematic analysis of measurement conditions and experimental parameters for determining single cell respiration rates, via the oxygen consumption rate (OCR) at single HeLa cells. Using scanning electrochemical microscopy (SECM), with a platinum UME as the probe, we employ a self-referencing measurement protocol, rarely employed in SECM, whereby the UME is repeatedly approached from bulk solution to a cell, and a short pulse to oxygen reduction reaction (ORR) potentials is performed near the cell and in bulk solution. This approach enables the periodic tracking of the bulk UME response to which the near-cell response is repeatedly compared (referenced), and also ensures that the ORR near the cell is performed only briefly, minimizing the effect of the electrochemical process on the cell. SECM experiments are combined with a finite element method (FEM) modeling framework, to simulate oxygen diffusion and the UME response. Taking a realistic range of single cell OCR to be 1x10-18 to 1x10-16 mol s-1, results from the combination of FEM simulations and self-referencing SECM measurements show that these OCR values are at - or below - the present detection sensitivity of the technique. We provide a set of model-based suggestions for improving these measurements in the future, but highlight that extraordinary improvements in the stability and precision of SECM measurements will be required if single cell OCR measurements are to be realized. TOC O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=146 SRC="FIGDIR/small/538172v1_ufig1.gif" ALT="Figure 1"> View larger version (42K): org.highwire.dtl.DTLVardef@14a6e59org.highwire.dtl.DTLVardef@192d44borg.highwire.dtl.DTLVardef@afb2caorg.highwire.dtl.DTLVardef@103131b_HPS_FORMAT_FIGEXP M_FIG C_FIG

cell biology↗

bioRxiv2022

Reproducible spatial structure formation and stable community composition in the cyanosphere predicts metabolic interactions

Understanding how microbial communities maintain stable compositional diversity is key for predicting community function. Studies from species pairwise interactions and synthetic communities indicate that metabolic interactions and spatial organisation can influence coexistence, but the relevance of these factors in more complex communities is unclear. Model systems often lack multi-species complexity, thereby making it difficult to study community diversity temporally. Here we used a spatially-organised cyanobacterial enrichment community to investigate compositional diversity and its stability. Over a year of passaging in media without significant carbon source, we found that the community maintains relatively high diversity, with 17 co-existing bacterial species. Using short and long read shotgun metagenomics sequencing from different time point samples, we have reconstructed complete genomes. Genomic annotation of these species revealed complementary metabolic functions involving carbon breakdown and vitamin biosynthesis suggesting interactions amongst community members. Using isolated species, we provide experimental support for carbon provision through cyanobacterial slime and growth on the component substrates by representative members of the Proteobacteria and Actinobacteriota phyla. Additionally, we experimentally show vitamin provision and uptake between prototrophic and auxotrophic members. We also found genomic capability for (an)oxygenic photosynthesis and sulfur cycling in several species. We show consistent formation of oxygen gradients across photogranule structures, supporting niches that can sustain these specific metabolic functions. These findings indicate that spatial niche formation and metabolic interactions enable maintenance of community compositional stability and diversity. SIGNIFICANCE STATEMENTMicrobes exist as species-diverse communities in nature and understanding their stability is an open challenge in microbial ecology. We established and maintained a spatially-organised, photosynthetic microbial community from a freshwater reservoir through long-term culturing in laboratory medium. We found that this community maintained a taxonomically-diverse set of 17 bacterial species. Combining genomic and physiological assays, we characterised a novel filamentous cyanobacterium capable of carbohydrate-rich slime secretion supporting growth of other microbes. We predict inter-species vitamin exchanges and identify sulfur cycling and alternative types of photosynthesis that are likely to be favoured in oxygen-free zones identified within the spatial structures. Our findings indicate that metabolic interactions and spatial structures can enable stable microbial coexistence in natural ecosystems.

microbiology↗

bioRxiv2020

Scanning ion conductance microscopy reveals differences in the ionic environments of gram positive and negative bacteria

This paper reports on the use of scanning ion conductance microscopy (SICM) to locally map the ionic properties and charge environment of two live bacterial strains: the gramnegative Escherichia coli and the gram-positive Bacillus subtilis. SICM results find heterogeneities across the bacterial surface, and significant differences among the grampositive and -negative bacteria. The bioelectrical environment of the B. subtilis was found to be considerably more negatively charged compared to E. coli. SICM measurements, fitted to a simplified finite element method (FEM) model, revealed surface charge values of -80 to -140 mC m-2 for the gram-negative E. coli. The gram-positive B. subtilis show a much higher conductivity around the cell wall, and surface charge values between -350 and -450 mC m-2 were found using the same simplified model. SICM was also able to detect regions of high negative charge near B. subtilis, not detected in the topographical SICM response and attributed to extracellular polymeric substance. To further explore how the B. subtilis cell wall structure can influence the SICM current response, a more comprehensive FEM model, accounting for the physical properties of the gram-positive cell wall, was developed. The new model provides a more realistic description of the cell wall and allowed investigation of the relation between its key properties and SICM currents, building foundations to further investigate and improve understanding of the gram-positive cellular microenvironment. O_FIG_DISPLAY_L [Figure 1] M_FIG_DISPLAY C_FIG_DISPLAY

microbiology↗