Biology subjects

Henshaw, R. J.

Publications and source records attributed to Henshaw, R. J..

9 recordsLinked to original sources

bioRxiv2026

Widespread attraction of marine bacteria to the macroalgae-derived polysaccharide fucoidan

Fucoidan is the second most abundant polysaccharide in brown macroalgae, contributing up to 50% of the dissolved organic matter released daily from these algae into the ocean, substantially influencing the marine carbon cycle. Due to its complex chemical structure, fucoidan is highly resistant to microbial degradation and accumulates on the surface of macroalgae, where it contributes to regulating their microbiome. Here, we used a range of microfluidic assays to quantify the chemotactic and physiological responses of marine bacteria to fucoidan. Our results reveal that all the strains tested (14 out of 14) are attracted to fucoidan produced by two different species of brown macroalgae. Attraction occurred only at high fucoidan concentrations (0.1 to 1 mg/mL), such as those expected in the immediate vicinity of algal surfaces, whereas low concentrations elicited no response or modest chemorepulsion. Although fucoidan did not support bacterial growth under our experimental conditions, it did not impair the utilization of other carbon sources. Together, these findings suggest that fucoidan gradients can act as chemical cues guiding marine bacteria toward the nutrient-rich microenvironment of macroalgal surfaces, pointing to a potential ecological role of fucoidan in shaping macroalgal microbiota, bacterial behavior, and ultimately carbon cycling in the ocean.

microbiology↗

bioRxiv2026

Bacterial capture and lysis on diatom spines reveal a suspension-feeding strategy

Phytoplankton contribute nearly half of global primary production and play a central role in ocean biogeochemistry. Although traditionally viewed as phototrophs, a growing body of evidence indicates that many phytoplankton are mixotrophic, supplementing photosynthesis with heterotrophic acquisition of nutrients and organic matter. Yet, the mechanisms enabling heterotrophic feeding in diatoms remain poorly understood. Here, we show that the chitinous spines of the diatom Conticribra weissflogii can serve as attachment sites for the bacterium Marinobacter adhaerens. Cryo-electron tomography and viability staining revealed that a substantial fraction of spine-associated M. adhaerens undergoes lysis. Consistent with bacterial lysis on the spines, Raman spectroscopy showed that diatom cells bearing spine-associated bacteria acquired more bacteria-derived nitrogen than uncolonized cells. Although microfluidic assays revealed a low bacterial affinity for the spines, our results suggest that attachment can be promoted by fucoidan deposits identified on the spines - a compound for which bacteria showed significantly higher binding affinity than chitin - as well as by their geometry, which encounter rate calculations show to be particularly efficient at intercepting bacteria. Together, these findings reveal a previously undescribed form of suspension-feeding in phytoplankton, reminiscent of the role of zooplankton pseudopods in prey capture. Diatom spines intercept bacteria from the surrounding water, retain them near the cell surface, and facilitate subsequent nutrient acquisition, probably through bacterial lysis. Our results expand the functional repertoire of diatom spines beyond defense and buoyancy, identifying spine-mediated bacterial capture as a previously overlooked pathway contributing to phytoplankton mixotrophy.

microbiology↗

bioRxiv2025

GUARDIANS OF THE CELL: COCCOSPHERE PREVENTS OPPORTUNISTIC BACTERIA ATTACK IN HEAVY CALCIFYING COCCOLITHOPHORE

Coccolithophores are responsible for 40-60% of marine calcium carbonate production. This occurs through the biomineralization of extracellular calcium carbonate plates that encase the cell in a structure called the coccosphere. Despite its central role in ocean biogeochemistry, the function of coccolithophore calcification remains unresolved. One hypothesis is that the coccosphere acts as a physical shield, deterring predators and microbes. While its protective role has been investigated against grazers and viruses, its function in bacterial defense remains untested. Here, we investigate the interaction between heavily calcified Coccolithus braarudii and the bacterial pathogen Phaeobacter inhibens, known for its lethal Jekyll and Hyde relationship with the bloom-forming Gephyrocapsa huxleyi. We find that in C. braarudii, no P. inhibens pathogenicity is observed--unless the algae are decalcified. Upon decalcification, the relationship with P. inhibens becomes pathogenic, leading to algal cell death. Mortality of decalcified cells is specific to interactions with P. inhibens and is attachment-mediated: no toxicity is observed when cells are exposed to P. inhibens supernatant or to growth-inhibiting concentrations of indole-3-acetic acid-- identified in the P. inhibens-G. huxleyi system. Attachment requirement is further supported by scanning electron microscopy, which reveals extensive bacterial colonization on decalcified but not on calcified C. braarudii with P. inhibens. These findings provide the first experimental evidence that the coccosphere acts as a physical barrier against bacterial attack, underscoring its defensive role in coccolithophores.

microbiology↗

bioRxiv2025

Bacteria induce an amoeboid phase in coccolithophores that persists after bloom collapse

Coccolithophores, who contribute approximately 1-10% of phytoplankton biomass, are crucial players in the oceans biogeochemical cycles. Significant contributions come from bloom-forming species including Gephyrocapsa huxleyi (formerly Emiliania huxleyi), which has served as a model system for investigating algal-bacterial and agal-viral interactions as well as algal fitness responses to environmental changes. Coccolithophores follow a biphasic lifecycle, existing as motile haploid and non-motile diploid phases. Here we characterize a third, amoeboid phase, using a combination of light, electron and phase amplitude modulation (PAM) microscopy. Using time-resolved imaging we captured the rapid morphological transition from a spherical haploid to an elongated motile amoeboid cell. Cell tracking revealed slower and more directional swimming compared to haploid cells. Amoeboid metamorphosis was triggered by exposure to bacteria, including strains isolated from G. huxleyi blooms and known G. huxleyi pathogens, but not by a range of classical phytoplankton stressors, including viral infection and oxidative stress. Further, the sub-population of haploids which switched to the amoeboid phase persisted past the rapid crash of the haploid population. This amoeboid phase was only observed in the primary bloom-forming coccolithophore species G. huxleyi and Geopharycapsa oceanica in stationary phase when exposed to high bacterial concentrations, typical of late-stage algal bloom events. Photophysiology of amoeboid cells was confirmed to be unaltered via PAM microscopy, indicating these cells are metabolically active. These findings highlight a previously uncharacterized morphotype in this important phytoplankton species and suggest that the amoeboid phase could be a bacteria-resistant morphotype following algal bloom collapse.

microbiology↗

bioRxiv2023

Early viral infection of cyanobacteria drives bacterial chemotaxis in the oceans

Interactions among marine microbes primarily occur through exudation and sensing of dissolved chemical compounds, which ultimately control ecosystem-scale processes such as biomass production, nutrient cycling, carbon fixation, and remineralization. Prior to lysis, viruses alter host metabolism, stimulating the release of dissolved chemical cues from intact plankton. However, the nature and degree of interactions between prelysis, virus-infected cells and neighbouring microbes remain unquantified. Here, we determine the impact of viral infection on dissolved metabolite pools from the marine cyanobacterium Synechococcus and the subsequent chemotactic response of heterotrophic bacteria using time-resolved metabolomics and microfluidics. Metabolites released from intact, virus-infected Synechococcus elicited vigorous chemoattractive responses from heterotrophic bacteria (Vibrio alginolyticus and Pseudoalteromonas haloplanktis), with the strongest responses occurring in the early infection stages and following cell lysis. We provide the first experimental observations of sustained chemotaxis towards live, infected Synechococcus, which is contrasted by no discernible chemotaxis toward uninfected Synechococcus. Finally, metabolite compounds and concentrations driving chemotactic responses were identified using a novel high-throughput microfluidic device. Our findings establish that prior to cell lysis, virus-infected picophytoplankton release compounds that significantly attract motile heterotrophic bacteria, illustrating a viable mechanism for resource transfer to chemotactic bacteria with implications for our understanding of carbon and nutrient flux across trophic levels.

biophysics↗

bioRxiv2022

Multiplexed microfluidic screening of bacterial chemotaxis

Microorganism sensing of and responding to ambient chemical gradients regulates a myriad of microbial processes that are fundamental to ecosystem function and human health and disease. The development of efficient, high-throughput screening tools for microbial chemotaxis is essential to disentangling the roles of diverse chemical compounds and concentrations that control cell nutrient uptake, chemorepulsion from toxins, and microbial pathogenesis. Here, we present a novel microfluidic multiplexed chemotaxis device (MCD) which uses serial dilution to simultaneously perform six parallel bacterial chemotaxis assays that span five orders of magnitude in chemostimulant concentration on a single chip. We first validated the dilution and gradient generation performance of the MCD, and then compared the measured chemotactic response of an established bacterial chemotaxis system (Vibrio alginolyticus) to a standard microfluidic assay. Next, the MCDs versatility was assessed by quantifying the chemotactic responses of different bacteria (Psuedoalteromonas haloplanktis, Escherichia coli) to different chemoattractants and chemorepellents. The MCD vastly accelerates the chemotactic screening process, which is critical to deciphering the complex sea of chemical stimuli underlying microbial responses.

ecology↗

bioRxiv2022

Dynamic mode structure of active turbulence

Dense suspensions of swimming bacteria exhibit chaotic flow patterns that promote the mixing and transport of resources and signalling chemicals within cell colonies. While the importance of active turbulence is widely recognized, the structure and dynamics of the resulting collective flows are the subject of intense investigation. Here, we combine microfluidic experiments with proper orthogonal decomposition (POD) analysis to quantify the dynamical flow structure of this model active matter system under a variety of conditions. In isotropic bulk turbulence, the modal representation shows that the most energetic flow structures dictate the spatio-temporal dynamics across a range of suspension activity levels. In confined geometries, POD analysis illustrates the role of boundary interactions for the transition to bacterial turbulence, and it quantifies the evolution of coherent active structures in externally applied flows. Beyond establishing the physical flow structures under-pinning the complex dynamics of bacterial turbulence, the low-dimensional representation afforded by this modal analysis offers a potential path toward data-driven modelling of active turbulence.

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↗