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Plastic pollution is widely recognised as a threat to life in our oceans and current trends indicate that the marine plastic burden and its ecological impact will continue to escalate. However, investigations of plastic pollution on marine microbial communities largely focus on microbes that attach to plastics, whereas impacts of plastic debris-leached chemicals remain poorly understood. We set out to investigate the impact of plastic leachate on natural communities of marine microbes using microcosm experiments, monitoring impacts on both the structure and function of this community. Our results show that exposure to leachate from polyvinyl chloride (PVC) matting negatively impact a broad group of photosynthetic microbes, both bacterial and eukaryotic, causing sharp declines in cell abundance, photosynthetic efficiency, and total chlorophyll. Further, PVC leachate impacted both taxonomic and functional diversity of the entire microbial community, with dramatic decreases in the abundance of key marine taxa including Synechococcus, SAR11 and members of the Rhodobacterales. Functional gene and metagenome-derived genome analyses showed that, while some key groups decline, fast-adapting, motile organisms were enriched, as were genes usually associated with pathogenicity and an increased capacity to metabolise organic compounds leached from PVC. These results reveal that PVC leachates have the potential to impact key organisms at the base of the marine food web, which could have significant flow-on effects for entire marine ecosystems. We are now investigating how specific components of the plastic leachate contribute to its toxicity to photosynthetic marine microbes. Also see: https://micro2022.sciencesconf.org/425929/document, In MICRO 2022, Online Atlas Edition: Plastic Pollution from MACRO to nano

Upper motor neuron injury damages the descending circuits connecting the brain to sensory and motor neurons responsible for sensing and interacting with the world. While spinal cord stimulation is showing extraordinary promise as a novel therapeutic to restore lost motor function following spinal cord injury, we have yet to fully characterize the mechanisms of its action or identify the limits of its therapeutic potential. Towards these ends I conducted a series of three studies which utilized spinal stimulation in novel subject populations to map the cervical spinal cord, identify and modulate aberrant spinal physiology, and enhance upper limb function. In the first study a group of SCI subjects with motor complete lesions, half of which had no measurable hand strength, received transcutaneous stimulation to the cervical spinal cord alone and in combination with the partial serotonergic agonist buspirone. Stimulation but not buspirone significantly improved hand function in subjects with measurable strength prior to the study and maintained hand strength for up to five months following treatment in more functional subjects. In the second study, two subjects who demonstrated improvement with transcutaneous stimulation but failed to maintain it 5 months after treatment, received epidural stimulators. The different properties and performance outcomes of the two forms of stimulation were compared in these severely impaired subjects. Finally in a cohort of rats, epidural stimulation was used to map the cervical spinal cord, track physiological changes in the spinal cord following a severe stroke injury to the motor cortex, and treat observed deficits in reaching success and muscle activity. While 20 Hz stimulation enhanced afferent derived spinal activity, only 1 Hz stimulation resulted in improved reaching success and muscle activity. Together these studies further our understanding, by identifying patient pools most receptive to spinal cord stimulation, characterizing the different properties and functional outcomes of transcutaneous versus epidural stimulation, and illustrating the potential to utilize spinal cord stimulation for other forms of upper motor neuron injury.

Additional file 1: Figure S1. Microcosm experimental design. PVC plastic leachate was prepared by cutting PVC matting into small pieces, leaching them in Turks Island Salt solution for 5 days, and 0.2 μm filtering to remove plastic pieces and microorganisms from the PVC leachate solution. Experimental bottles containing seawater were set up by adding the PVC leachate in two different concentrations for 1% PVC leachate and 10% PVC leachate treatments, adding ZnCl2 in two concentrations for ZnL (0.13 mg L-1) and ZnH (1.3 mg L-1) treatments, and having one no addition seawater control. Quadruplicate replicate bottles were set up for each treatment and the control and incubated in an outside tank with light and temperature to mimic the conditions of the seawater source (issues with two ZnH treatment bottles meant they were not able to be included in the final analysis). Figure S2. Gating strategies used to quantify photosynthetic communities via flow cytometry analysis. A representative sample of a natural population (panel 1) illustrates how Chlorophyll and phycoerythrin (PE) autofluorescence were used to discriminate two groups of pigment-containing organisms: photosynthetic eukaryotes and Synechococcus. Specifically, eukaryotes were distinguished from Synechococcus based on their high Chlorophyll autofluorescence and relatively low PE fluorescence (panel 2). From there different eukaryotic communities were then discriminated based on FSC and PE content (panel 3). Synechococcus communities were discriminated based on PE and SSC content (panel 4). The gating strategy outlined was used for all of the samples. Figure S3. Gating strategies used to quantify heterotrophic bacterial and viral communities via flow cytometric analysis. A representative sample of a natural population (panel 1) illustrates how Sybr Green I fluorescence intensity and violet SSC were used to discriminate viral and bacterial communities. Contour plots of these two communities enabled identification of 2 different populations of bacteria, low DNA-containing bacteria (LDNAb) and high DNA-containing bacteria (HDNAb) (panel 2), and 5 distinct viral populations (panel 3). The gating strategy outlined was used for all the samples. Figure S4. Impact of PVC plastic leachate and zinc treatments on various flow cytometric populations. Changes in (a) photosynthetic Nano-eukaryote (NEUK) and phycoerythrin-rich eukaryote (PeEUK) population abundances and in (b) the ratio of Synechococcus to total eukaryotic primary producers community abundances are shown during the 6-day experiment. The effect of the different treatments on (c) the ratios between HDNAb vs LDNAb bacterial communities (HL_ratio) and total viral to total bacterial communities (VB_ratio), and their impact on (d) the five different viral populations are presented over the 6-day experiment. Data points are derived from the daily mean flow-cytometrically derived abundance (cells ml-1) of quadruplicate, biologically-independent samples (except ZnH for which just 2 replicates are available) for each day of the 6-day experiment. Error bars on each point represent the standard deviation. The lower-case letters (a-c) on panels a, b and c indicate which treatments were found to be statistically different (p < 0.01) from each other at the final time point (Additional file 2: Table S5). Significance was calculated with an ANOVA test followed by pairwise t-test and p-value false discovery rate (FDR) corrected. Figure S5. Composition of the bacterial and eukaryotic communities before (T0) and after exposure (day six) to PVC leachate and zinc. Boxplots indicate the average Shannon diversity for the (a) bacterial and (b) eukaryotic communities for each of the treatments. Different lower-case letters within the panels indicate a significance difference (p < 0.01, FDR corrected, Additional file 2: Table S7) from the control in the Shannon diversity. Non-metric multidimensional scaling (nMDS) plots are based on a Bray-Curtis dissimilarity matrix of the rarefied (c) bacterial and (d) eukaryotic community composition for each treatment bottle with axes indicating the percentage of explanation for the first two components. Stacked bar plots show the shift of (e) bacterial classes that contribute to > 1% of the total relative abundance per samples and the shift of (f) eukaryotic phyla that contribute to > 1% of the total relative abundance across treatments. The communities experienced changes in the relative abundance of some bacterial groups during the course of the experiment (from T0 to SW on day six in Fig. S5), likely due to bottle effects; however, these changes were less pronounced than the treatment effects. Figure S6. Bacterial community composition across the different treatments. Stacked bar plots show the bacterial Amplicon Sequence Variants (ASVs) that contribute to > 1% of the total relative abundance for seawater replicates at T0 and each treatment sample replicate at day 6. Figure S7. Eukaryotic community composition across the different treatments. Stacked bar plots show the eukaryotic Amplicon Sequence Variants (ASVs) that contribute to > 1% of the total relative abundance for seawater replicates at T0 and each treatment sample replicate at day 6. Figure S8. Average doubling times (h) for the isolated bacterial MAGs aggregated at the family level. Doubling times were calculated based on codon frequencies of multiple, highly expressed ribosomal genes for each MAG following the R package gRodon.