Biology subjects

Melaugh, G.

Publications and source records attributed to Melaugh, G..

4 recordsLinked to original sources

bioRxiv2025

Environmental dependence of colony morphologies in Labyrinthula species

Labyrinthula species are protist organisms found across a variety of marine environments whose defining characteristic is the secretion of an extracellular ectoplasmic net. Under certain conditions, colonies form a spatial network of tracks through which cells move bidirectionally. We show that this network morphology depends on the presence of a liquid overlay, with air exposed colonies exhibiting instead a dense, aggregated morphology. We demonstrate dynamic restructuring between these two morphologies upon addition or removal of the liquid overlay, and investigate growth behaviour under varying nutrient conditions. Given the inter-tidal environment of certain seagrass species colonised by Labyrinthula, our results may shed light on the relationship between this organism and its seagrass host, for which it is an opportunistic pathogen associated with seagrass wasting disease.

biophysics↗

bioRxiv2023

Tunable living bacterial networks: A multi-scaled description of their self-assembly and mechanical behaviour

Bacterial aggregate formation and surface accumulation are increasingly viewed as alternative pathways for biofilm colonization. However, little is known about the dynamics of bacterial aggregate cluster-cluster assembly and their subsequent microstructural and mechanical properties. To this end, we studied experimentally and computationally an aggregating bacterial system that forms a space-spanning interconnected network via cluster-cluster assembly. By controllably inducing bacterial filamentation, we aimed to understand how cell length distribution and cell surface hydrophobicity control the dynamics of aggregation and sedimentation, as well as the microstructure and mechanics of the settled bacterial networks. We found that filamentation lowers the percolation threshold, leading to gelation at a lower number density with distinct assembly dynamics and lower network connectivity. Furthermore, we analyzed the mechanical properties of the bacterial networks. Static stress tests reveal three yielding modes: discrete cluster-cluster disassembly, collective delamination, and sub-regional network fracture. The yielding modes are consistent with the gel-like viscoelastic properties of the cluster-cluster assembled networks observed during macroscale rheometry. In particular, we observe a scaling relationship between the storage modulus and the volume fraction, characteristic of an attractive rod gel. Our experimental observations are supported by Langevin dynamic simulations, providing mechanistic insights into the factors determining network self-assembly and connectivity. Our findings elucidate the gel-like structure-function dynamics in cluster-cluster aggregated bacterial systems and underscore the fundamental importance of filamentation in their properties and mechanical behavior.

biophysics↗

bioRxiv2022

Distinct types of multicellular aggregates in Pseudomonas aeruginosa liquid cultures

Pseudomonas aeruginosa forms suspended multicellular aggregates when cultured in liquid media. Such aggregates may be important in disease, and/or as a pathway to biofilm formation. The polysaccharide Psl and extracellular DNA (eDNA) have both been implicated in aggregation, but previous results depend strongly on the experimental conditions. Here we develop a quantitative microscopy-based method for assessing changes in the size distribution of suspended aggregates over time in growing cultures. For exponentially growing cultures of P. aeruginosa PAO1, we find that aggregation is mediated by cell-associated Psl, rather than by either eDNA or se-creted Psl. These aggregates arise de novo within the culture via a growth process that involves both collisions and clonal growth. They are "non-cheatable" since Psl non-producing cells do not aggregate with producers. In contrast, we find that stationary phase (overnight) cultures contain a different type of multicelullar aggregate, in which both eDNA and Psl mediate cohesion. Our findings suggest that the physical and bi-ological properties of multicellular aggregates may be very different in early-stage vs late-stage bacterial cultures.

microbiology↗

bioRxiv2022

Pinning transition in biofilm structure driven by active layer dynamics

Surface-attached communities of microbes, known as biofilms, are diverse in their morphologies. Characterising distinct types of biofilm spatial structure, and understanding how they emerge, can shed light on the fundamental biological and biophysical mechanisms involved, and can improve our understanding of evolution in biofilms. Here, we perform long-time individual-based simulations of growing biofilms. We observe distinct types of biofilm spatial structure depending on the parameters, and we classify these into three phases according to the behaviour of the active layer of growing cells at the biofilm interface. In the unpinned phase, the biofilm is smooth and the active layer is unbroken with no gaps. In the transiently pinned phase, short-lived gaps in the active layer arise, which can cause local parts of the biofilm interface to pin, or become stationary relative to the moving front. In the pinned phase these pinning sites persist, leading to fingering of the biofilm interface. We show that pinning arises due to the dynamical behaviour of active layer gaps, and observe that the relative magnitudes of the active layer thickness and the active layer fluctuations are important in this process. We demonstrate a direct connection between biofilm pinning and interface roughness, and we show that the pinning phase transition is well described by a control parameter that combines the average and standard deviation of the active layer thickness. Taken together, our work suggests a role for active layer dynamics in controlling pinning of the biofilm interface and hence biofilm morphology.

biophysics↗