Biology subjects

Cunliffe, M.

Publications and source records attributed to Cunliffe, M..

7 recordsLinked to original sources

bioRxiv2025

Cell wall forming chitin synthases in a chytrid fungus

Chitin is a critical structural component of fungal cell walls, yet our understanding of its synthesis across the kingdom Fungi remains limited. Here, we investigate chitin synthase diversity, transcription and localisation in the saprotrophic chytrid Rhizoclosmatium globosum (Rg), expanding insights into fungal cell wall biology beyond Dikaryan models. We identified 20 chitin synthase genes in the Rg genome, including canonical Division I and II types, and a distinctive chitin synthase gene containing a glycoside hydrolase domain linked to {beta}-glucan synthesis. Transcriptomic analysis through zoospore, germling and immature thallus developmental stages revealed stage-specific expression patterns, with active gene diversity correlating with increasing morphological complexity. Using electroporation-based transformation and fluorescent fusion constructs, we demonstrated successful expression and localisation of two chitin synthases during cell development. Localisation patterns showed dynamic redistribution from cytoplasmic dispersion in early encysted cells to concentrated signals at the sporangium wall. Expression in the apophysis and at the apophysis-sporangium junction indicates the importance of these structures in cell maintenance. Our findings highlight functional specialisation among chitin synthases and underscore the importance of cell wall integrity in chytrid development. This work establishes Rg as a genetically tractable model for studying chytrid cell biology and contributes to broader understanding of fungal evolution and cell wall dynamics.

microbiology↗

bioRxiv2025

Phagocytosis repurposed: infection strategies in a globalmarine diatom-parasite interaction

Microbial host-parasite interactions shape global biogeochemical cycles, yet their cellular and evolutionary mechanisms remain poorly understood. Here, we developed a novel model pathosystem to explore the interaction between the globally distributed eukaryotic microparasite, Pirsonia, and its host, the bloom-forming diatom, Coscinodiscus. Culture conditions recapitulated Pirsonias rapid life cycle in vitro and live-cell imaging enabled quantitative assessments of infection dynamics and host mortality. To investigate the genetic basis of this interaction, we assembled the Pirsonia genome and identified unique genetic innovations relative to their oomycete relatives. Time-resolved dual RNA-Seq enabled tracking of parasite gene expression through the infection cycle and revealed an upregulation of an expanded multi-gene family of integrin-like proteins in Pirsonia zoospores, analogous to the variable surface proteins in other parasitic lineages. Genes upregulated during infection were associated with cytoskeletal dynamics and drug inhibition assays confirmed that actin is required for host infection, consistent with the presence of parasitic pseudopodia on infected hosts. The dependence on both actin-based phagocytic mechanisms and parasitic-like surface proteins highlights Pirsonias intermediate state between predator and parasite, providing new insights into the evolution of parasite strategies and the complex cellular interactions controlling parasitic shunts in marine trophic networks.

evolutionary biology↗

bioRxiv2024

Seasonal niche overlap of diverse facultative antagonistic bacteria of diatoms in a productive coastal ecosystem

Biotic interactions between microbes underpin marine ecosystem health, governing the flux of carbon and other nutrients in the ocean. However, studying aquatic microbial interactions is challenging. Model systems can provide in depth understanding of the mechanisms driving such associations. Yet, insights of the prevalence and co-occurrence dynamics of laboratory model systems in natural ecosystems remain limited. By leveraging 16S and 18S metabarcoding combined with phylogenetic analysis, we assessed the environmental presence of facultative bacterial pathogens of one of the most globally abundant phytoplankton groups, the diatoms. Sampling microbial assemblages in a productive coastal ecosystem over the course of an annual cycle, we detected multiple algicidal bacteria that frequently exhibited overlapping co-occurrences. Together, these bacteria positively correlated with members of the potentially toxic genus Pseudo-nitzchia, as well as temperature. Our study indicates that antagonistic bacteria occupy shared temporal niches and demonstrates the need to consider their cumulative impacts on diatom population health, including in future ocean conditions.

ecology↗

bioRxiv2024

Evolutionary and biological mechanisms underpinning chitin degradation in aquatic fungi

Fungal biology underpins major processes in ecosystems. The Chytridiomycota (chytrids) is a group of early-diverging fungi, many of which function in ecosystems as saprotrophs processing high molecular weight biopolymers, however the mechanisms underpinning chytrid saprotrophy are poorly understood. Genome sequences from representatives across the group and the use of model chytrids offers the potential to determine new insights into their evolution. In this study, we focused on the biology underpinning chitin saprotrophy, a common ecosystem function of aquatic chytrids. The genomes of chitinophilic chytrids have expanded inventories of glycoside hydrolase genes responsible for chitin processing, complemented with bacteria-like chitin-binding modules (CBMs) that are absent in other chytrids. In the model chitinophilic saprotroph Rhizoclosmatium globosum JEL800, the expanded repertoire of chitinase genes is diverse and almost half were detected as proteins in the secretome when grown with chitin. Predicted models of the secreted chitinases indicate a range of active site sizes and domain configurations. We propose that increased diversity of secreted chitinases is an adaptive strategy that facilitates chitin degradation in the complex heterologous organic matrix of the arthropod exoskeleton. Free swimming R. globosum JEL800 zoospores are chemotactic to the chitin monomer N-acetylglucosamine and accelerate zoospore development when grown with chitin. Our study sheds light on the underpinning biology and evolutionary mechanisms that have supported the saprotrophic niche expansion of some chytrids to utilise lucrative chitin-rich particles in aquatic ecosystems and is a demonstration of the adaptive capability of this successful fungal group.

evolutionary biology↗

bioRxiv2023

Cryptic bacterial pathogens of diatoms peak during senescence of a winter diatom bloom

Diatoms are globally abundant algae that form extensive blooms in aquatic ecosystems. Certain bacteria behave antagonistically towards diatoms, killing or inhibiting their growth. Despite their crucial implications to diatom health and bloom control, insight of the prevalence and dynamics of antagonistic bacteria in nature is lacking. We report an ecosystem assessment of the diversity and seasonal patterns of bacterial antagonists of diatoms via regular plaque-assay sampling in the Western English Channel (WEC), where diatoms frequently bloom. Unexpectedly, peaks in antagonist detection did not occur during characteristic spring blooms, but coincided with a winter bloom of Coscinodiscus, suggesting bacterial pathogens likely influence distinct diatom host populations. We isolated multiple antagonists, spanning 4 classes and 10 bacterial orders. Many species had no prior reports of pathogenicity towards diatoms, and we verified diatom growth inhibitory effects of 8 isolates. In all cases tested, pathogenicity was activated by pre-exposure to diatom organic matter. Discovery of widespread cryptic antagonistic activity evident under specific conditions, indicates that bacterial pathogenicity towards diatoms is more prevalent than previously recognised. Finally, mining Tara Oceans data revealed the global biogeography of WEC antagonists and co-occurrence patterns with diatom hosts. Our study indicates that multiple, diverse antagonistic bacteria have potential to impact diatom growth and bloom dynamics in marine waters globally.

microbiology↗

bioRxiv2021

A cellular and molecular atlas reveals the basis of chytrid development.

The chytrids (phylum Chytridiomycota) are a major early-diverging fungal lineage of ecological and evolutionary importance. Despite their importance, many fundamental aspects of chytrid developmental and cell biology remain poorly understood. To address these knowledge gaps, we combined quantitative volume electron microscopy and comparative transcriptome profiling to create an atlas of the cellular and molecular basis of the chytrid life cycle, using the model chytrid Rhizoclosmatium globosum. From our developmental atlas, we show that zoospores exhibit a specialised biological repertoire dominated by inactive ribosome aggregates, and that lipid processing is complex and dynamic throughout the cell cycle. We demonstrate that the chytrid apophysis is a distinct subcellular structure characterised by high intracellular trafficking, providing evidence for division of labour in the chytrid cell plan, and show that zoosporogenesis includes animal like amoeboid cell morphologies resulting from endocytotic cargo transport from the interstitial maternal cytoplasm. Taken together, our results reveal insights into chytrid developmental biology and provide a basis for future investigations into early-diverging fungal cell biology.

developmental biology↗

bioRxiv2019

Chytrid rhizoid morphogenesis is adaptive and resembles hyphal development in ‘higher’ fungi

Fungi are major components of the Earths biosphere [1], sustaining many critical ecosystem processes [2, 3]. Key to fungal prominence is their characteristic cell biology, our understanding of which has been principally based on higher dikaryan hyphal and yeast forms [4-6]. The early-diverging Chytridiomycota (chytrids) are ecologically important [2, 7, 8] and a significant component of fungal diversity [9-11], yet their cell biology remains poorly understood. Unlike dikaryan hyphae, chytrids typically attach to substrates and feed osmotrophically via anucleate rhizoids [12]. The evolution of fungal hyphae appears to have occurred from lineages exhibiting rhizoidal growth [13] and it has been hypothesised that a rhizoid-like structure was the precursor to multicellular hyphae and mycelial feeding in fungi [14]. Here we show in a unicellular chytrid, Rhizoclosmatium globosum, that rhizoid development has equivalent features to dikaryan hyphae and is adaptive to resource availability. Rhizoid morphogenesis exhibits analogous properties with growth in hyphal forms, including tip production, branching and decreasing fractal geometry towards the growing edge, and is controlled by {beta}-glucan-dependent cell wall synthesis and actin polymerisation. Chytrid rhizoids from individual cells also demonstrate adaptive morphological plasticity in response to substrate availability, developing a searching phenotype when carbon starved and exhibiting spatial differentiation when interacting with particulate substrates. Our results show striking similarities between unicellular early-diverging and dikaryan fungi, providing insights into chytrid cell biology, ecological prevalence and fungal evolution. We demonstrate that the sophisticated cell biology and developmental plasticity previously considered characteristic of hyphal fungi are shared more widely across the Kingdom Fungi and therefore could be conserved from their most recent common ancestor.

developmental biology↗