Master of Science thesis defences start with an online public talk that all are welcome to attend.

Recent and upcoming thesis defences are shared below, along with times and dates of any upcoming public talks or events.

Upcoming Public Talks:

August 26 @ 1 p.m. in Barclay B021

Ryan Wahl, MSc candidate, presents...

"Does hypoxia elicit a whole-animal ketogenic response in three evolutionarily distinct fish?"

(detailed description is forthcoming)


Using multi-proxy measures of lake sediments to identify environmental changes in protected watersheds of British Columbia, Canada ~ Alexandra Di Lonardo, MSc (2022)

Abstract: Paleolimnology uses lake sediments to recognize environmental trends through time. This is useful in watersheds with a knowledge gap of historical environmental conditions or missing perspectives of ecosystem response to a period of change. Cameron Lake sediments were used to identify historical trends of Didymosphenia geminata valves in a mat-prone watershed. The core represented approximately 600 years of sediment accumulation and findings demonstrated that D. geminata was a historical member of the diatom community. Though in low abundance in older sediment, valve concentrations increased in the early 1900s and peaked at ~1990s, coinciding with observations of mats in the watershed. Geochemical proxy measures were then analyzed to explore if watershed disturbance was a driver of environmental conditions favouring D. geminata mat formation. No clear geochemical trends were identified, thus watershed disturbance was not associated with recent D. geminata mats. Cultus Lake has experienced urbanization in and around the watershed, resulting in cultural eutrophication. Over the past century, water quality metrics suggested a decline in hypolimnetic oxygen, however there is a lack of temporal knowledge on the biological responses to eutrophication. Cultus Lake sediments were analyzed for temporal trends in benthic invertebrate assemblages. Chironomid assemblages shifted from oligotrophic, high oxygen favoring taxa to an assemblage indicative of eutrophic and low oxygen conditions. This shift began in the 1920s, coinciding with the agricultural activities in the area. A more recent assemblage shift in the 1970s indicated that the assemblage is now dominated by generalist taxa. Findings suggest the benthic environment of Cultus Lake has less oxygen availability, and this temporal information can be used in future lake management and recovery plans for species of concern at Cultus Lake.

Supervisor: Dr. Joshua Kurek, Associate Professor ~ ECAB Lab @ MtA

Legacy Contaminants in Brook Trout from Remote New Brunswick Lakes ~ Meghan Fraser, MSc (2022)

Abstract: DDT and mercury are legacy contaminants that are persistent in the environment for decades or longer. They may impact food webs through bioaccumulation, biomagnification, and chronic toxic effects in exposed biota. DDT was applied aerially on large scales to the conifer forests in north-central New Brunswick between 1952 and 1968 for pest control in the forestry sector. I sampled seven lakes in the summers of 2020 and 2021 to investigate the impact of historical DDTs on the present day aquatic environment. I sampled brook trout, aquatic invertebrates, zooplankton, and lake surface sediments. I found DDTs were up to ~14 times higher in brook trout muscle tissues from lakes where DDTs were applied to the watershed compared to reference lakes. DDTs in brook trout exceeded CCME guidelines by up to ~22 times. Mercury is a common contaminant of concern and delivered to lakes by atmospheric transport. Most mercury originates from anthropogenic activities, including burning fossil fuels, and mining or smelting metals rather than natural geogenic sources. I sampled brook trout from seven New Brunswick lakes in 2020, and found mercury levels comparable to similar studies in eastern North America. Mercury in brook trout exceeded CCME guidelines for methylmercury by up to ~12 times. Using DDT and mercury measures, we can further our understanding of legacy contaminants in New Brunswick lake environments.

Supervisor: Dr. Joshua Kurek, Associate Professor ~ ECAB Lab @ MtA


"Brook trout and DDT: a connection between aquatic food-webs and legacy contaminants", Meghan Fraser, Joshua Kurek, Karen Kidd, Christopher Edge. The Atlantic Society of Fish and Wildlife Biologists 58th AGM and Conference, PEI. Presented October 2021.

Influence of Diel Thermal Variability on Growth, Development, Swimming Performance and Stress Response in Salmonid Fishes ~ Sean Andrew, MSc (2022)


Abstract: Accurately understanding the biological effects of temperature is important for effective species conservation, especially in this era of climate warming. Traditionally, temperature effects on fishes have been understood using fish held at stable temperatures. In many natural freshwater fish habitats, however, temperature cycles daily. Diel thermal cycles can be as wide as 5-9oC in key salmonid habitats like the Miramichi River in New Brunswick. To date, little is known about the biological effects of these diel thermal cycles on fishes.

In my thesis, I investigated the growth, development, and swimming performance of Atlantic salmon (Salmo salar) under 16-21 and 19-24oC diel thermal cycles (representing cool and warm sites in the summer at the Miramichi). Additionally, I examined the stress response and post-angling survival of brook trout (Salvelinus fontinalis) after exposure to diel cycles with different daily thermal maximums (24, 26, or 27oC). I found that Atlantic salmon grew at similar rates at 16-21 and 19-24oC as parr, but smolts grew slower at 19-24oC especially for those from the relatively cooler Restigouche river compared to those from Miramichi. Atlantic salmon swimming efficiency was insensitive to acute warming or acclimation thermal cycle while sustainable swimming capacity stayed >90% (of the maximum) at the warmest test temperature (24oC) for both acclimation groups.

Overall, Atlantic salmon appeared more resilient to warm temperatures than thought based on stable temperature experiments. Brook trout increased metabolic rate above resting levels after 26 or 27oC exposure which also increased some reflex impairments predicting greater post-angling mortality. Tmax may thus be an important factor to consider in closing/opening recreational fisheries which have considered some river temperature parameters.

Supervisors: Dr. Andrea Morash, Assistant Professor (Mount Allison) and Dr. Suzie Currie, Professor and Dean of Science (Acadia)


“Effects of Daily Tmax on Metabolic Rate and Indicators of Survival Post-Chase for Brook Trout”. Canadian Society of Zoologists conference. Presented May 2022.

“Efficiency and Limits of Sustainable Swimming in Atlantic salmon (Salmo salar) under Warm Summer Environments with Diel Thermal Variability”. Canadian Society of Zoologists conference. Presented May 2021.

Prevalence of the Zoonotic Diseases Leptospirosis and Borreliosis in the Maritimes of Canada ~ Samantha Bishop, MSc (2022) 

Abstract: Centered on a One Health approach; focusing on environment, animal, and human health; the aim of this study was to investigate the prevalence of the globally important infectious diseases Leptospirosis and Borreliosis.  The risk of contracting leptospirosis in Canada has been increasing over the last 30 years, with New Brunswick reporting an increase in infected dogs with leptospirosis, and an increased risk in contracting Lyme borreliosis due to expanding tick populations.

To determine the prevalence of these spirochetes in the province, multiple methodologies and areas of interest were examined. Leptospira borgpetersenii was sequence confirmed in 2.7% of wildlife and 3.6% of ticks (Dermacentor variabilis, Ixodes cookei, and Ixodes scapularis).  Dog serum was tested for the presence of antibodies against Leptospira spp., in which 19.3% were positive. Borrelia bissettiae was also sequence confirmed in one meadow vole (Microtus pennsylvanicus) and one deer mouse (Peromyscus maniculatus).

Understanding the risk of infection by Borrelia spp. of our local wildlife species becomes directly relevant to human health, as it can cause Lyme disease in humans. In its disseminated form, it can affect organs such as the heart, causing what is known as Lyme carditis, a rare but potentially fatal outcome when diagnoses are missed.

This study presents a case of fatal severe heart disease following suspected untreated Lyme carditis of a 17-year-old female from Nova Scotia, Canada. Together, these results elucidate a widespread rate of infection in the wildlife species, sentinel species, and tick species of New Brunswick.

Supervisor: Dr. Vett Lloyd, Professor ~ Lloyd Tick Lab

Presentations/News: “Incidence, location, wildlife reservoir species and biogeographical modeling of leptospirosis in the Canadian Maritimes”, Canadian Public Health Association's Infectious Disease & Climate Change webinar series. Presented and recorded on May 26, 2021.
Recording can be found here: YouTube recording of presentation

Exploring methods of direct detection of Borrelia in dogs and horses ~ Jessica Thomas Ebbett, MSc (2021)

Abstract: Borrelia, the causative agent of Lyme disease, is a complex spirochete with extensive abilities to evade the immune system of infected mammals. It is transmitted to hosts by ticks of the Ixodes spp. which typically acquire the bacteria during their first (larval) or second (nymphal) blood meal on infected reservoir species.

In dogs and horses, many cases of Lyme disease are asymptomatic and those that are symptomatic causes a wide array of non-specific symptoms, which can be mistakenly attributed to other diseases and whose range can be broadened even further when coinfection with other tick-borne illnesses occurs. Lyme disease can cause polyarthritis, fever, anorexia, neurological signs, and long-term sequelae such as Lyme nephropathy in dogs and neuroborreliosis in horses. Current diagnostic methods rely solely upon serology for detection; however, serology depends upon the ability of the host to produce antibodies against Borrelia, which does not always occur, for a variety of reasons. Additionally, serological diagnostic methods are unable to readily distinguish between a current and previously resolved infection or reinfection.

The aim of this study was to investigate methods of direct detection of Borrelia; such methods would provide unequivocal diagnosis and enable veterinarians and clinicians to institute early treatment which is associated with a much higher rate of cure. Periodontal swabs of dogs and horses and urine samples of dogs were cultured and samples processed for further evaluation by Dieterle staining, immunohistology (immunostaining), fluorescence in-situ hybridization (FISH), and nested polymerase chain reaction (nPCR). Slides were evaluated for the presence of spirochetes and the round body (RB) form. Sensitivity and specificity were calculated for each method of direct detection against the clinical reference standard of enzyme-linked immunosorbent assay (ELISA).

Sensitivity and specificity using ELISA as the reference standard for Dieterle stained canine samples was 100% and 90%, respectively; for immunostained canine samples, 41% and 90%, respectively; and for FISH samples, 38% and 100%, respectively. When compared with ELISA as the reference standard, sensitivity and specificity for Dieterle stained equine samples was 60% and 33%, respectively; for immunostained equine samples, 10% and 100%, respectively; and for FISH samples, 0% and 100%, respectively. None of the cultures generated sequence-confirmed amplicons by nPCR.

While none of the methods of direct detection can be used in isolation to replace the current standard of ELISA, each possessed its own advantages and, used in conjunction with ELISA might have the potential to aid in a more accurate diagnosis, thereby enabling prompt treatment for the patient by veterinarians.

Supervisor: Dr. Vett Lloyd, Professor ~ Lloyd Tick Lab

The impact of stress on glutamate synapses in the rat dorsomedial hypothaloamus nucleus ~ Tenea Welsh, MSc (2021)

Abstract: Prenatal stress can predispose offspring to adverse health conditions, such as obesity, and alter brain development and function in the offspring. Until now, few studies have examined the potential neurological basis between prenatal stress and offspring obesity. The dorsomedial hypothalamus (DMH) is a key brain region involved in appetite regulation and the stress response, and may be a neurological link between prenatal stress and increased metabolic risk in offspring.

To investigate this link, Sprague-Dawley rats were exposed to a chronic variable stress paradigm in the third week of gestation. This stress paradigm was adapted from a previous study that produced rodent offspring who were obese and exhibited adverse metabolic conditions. We proposed that our stress paradigm would modulate neuronal activity and synaptic transmission in the DMH. Using patch clamp electrophysiology, we obtained whole-cell recordings from DMH neurons from male and female rat offspring, age postnatal day 21-38. We investigated changes in neuronal excitability, basal GABA and glutamate synaptic transmission, and synaptic plasticity, the latter was achieved by assessing evoked current amplitude following high frequency stimulation (HFS).

Results suggested that prenatal stress decreased neuronal excitability in males, but not females, by increasing the after-hyperpolarization amplitude. Prenatal stress reduced spontaneous GABA signaling only in males, and reduced spontaneous glutamate signaling in both males and females. As for synaptic plasticity at GABA synapses, prenatal stress enhanced GABA signaling in males and reduced GABA signaling in females following HFS. At glutamate synapses, both males and females exhibited enhanced signaling following HFS. Our findings show that prenatal stress alters neuronal activity in the DMH in a sex-dependant manner, and may have potentially revealed a neurological link between prenatal stress and the development of adverse health conditions.

Supervisor: Dr. Karen Crosby, Assistant Professor ~ Neurophysiology

Dynamics of Intertidal Biofilm in Relation to Semipalmated Sandpiper (Caldris pusilla) Migratory Stopover and Assessments of Benthic Invertebrate and Biofilm Nutritional Content in the Upper Bay of Fundy, Canada ~ Matthew Mogle, MSc (2021)

Abstract: The upper Bay of Fundy is a critical stopover site for Semipalmated Sandpipers (Calidris pusilla) during their post-breeding southward migration. Abundant nutritious prey is essential for these sandpipers to build fat stores needed to complete their journey to South America. Microphytobenthic biofilm is the base of the intertidal mudflat food web and serves as the major source of energy and nutrition for the mudflat biotic community. Therefore, the standing crop and nutritional quality of MPB biofilm plays a critical role in supporting a prey base for Semipalmated Sandpipers.

Previous studies report that the standing crop and the fatty acid composition of MPB biofilm shows pronounced spatial differences. To further investigate variation in MPB biofilm, we assessed spatiotemporal trends in MPB biofilm primary production, standing crop and nutritional quality (lipid, protein, and carbohydrate content) before, during, and after sandpipers pass through the Bay of Fundy. Additionally, we compared MPB biofilm caloric content and nutritional quality to invertebrate prey types: polychaetes and Corophium volutator.

Results suggested that the nutritional quality of MPB biofilm is highly variable. Notably, MPB biofilm lipid content was at least 50% lower in 2020 than in 2019. This was likely related to the lower MPB biofilm standing crop in 2020, potentially driven by hot, dry weather conditions, which negatively impacts diatom growth. Impacts of climate change on MPB biofilms will have implications for the food webs dependent on MPB biofilm as a major source of chemical energy input. Prey types differed significantly in nutritional composition and caloric content, with invertebrates having more proteins and lipids and biofilm being more carbohydrate-rich. This work improves our understanding of variation in MPB biofilm nutritional quality and standing crop as well as the relative nutritional quality of common Semipalmated Sandpiper prey items.

Supervisors: Dr. Diana Hamilton, Professor ~ research website ~ and Dr. Myriam Barbeau

Matt is currently working in Maine as the research director at Shaw Institute, an environmental and public health NGO in Maine.  Matt has two papers in preparation for publication, and has given an invited presentation on biofilm and birds at a recent Environment and Climate Change Canada symposium.

Movement, Habitat Use and Metabolic Condition of Semipalmated Sandpiper (Calidris pusilla) during migratory stopover and non-breeding periods ~ Rebeca Linhart, MSc (2021)

Abstract:  Semipalmated Sandpipers (Calidris pusilla) are Arctic-breeding shorebirds that use stopover sites throughout Canada during their annual fall migration to non-breeding areas in South America. Population declines have been recorded throughout the range, especially from the Eastern breeding population which stops in Atlantic Canada and spends in non-breeding period in Eastern South America. This has prompted studies of habitat use to determine sources of decline and necessary conservation action.

The Bay of Fundy is internationally recognized as important for sandpipers on stopover, but it’s use by juvenile sandpipers is less understood. Comparatively little attention has been given to secondary sites throughout the region. Furthermore, movement and habitat use on the non-breeding grounds is largely unstudied.

Using the Motus Wildlife Tracking System I tracked sandpipers at sites within and outside the Bay of Fundy to examine differences in stopover strategy and habitat use between adults and juveniles. I also assessed metabolic condition and dietary niche of migrant sandpipers, as well as foraging behaviour and food availability between the two study regions in Atlantic Canada. Additionally, I studied the daily movements and behaviour of non-breeding sandpipers in Northeast Brazil to determine what influences movements and which habitats were important. I also assessed plasma triglyceride values and successfully tracked sandpipers on northward migration.

There were differences in diet and habitat use between adult and juvenile sandpipers on stopover, though juveniles appeared to gain weight just as efficiently as adults. Birds tagged at coastal sites displayed different stopover strategies than those tagged within the Bay of Fundy, with some sandpipers exclusively using coastal sites throughout their stopover and others choosing to move into the bay. Sandpipers at the Bancos dos Cajuais in Brazil appeared to use daylight and tidal height as movement indicators and made use of highly degraded areas, and some sandpipers may be fueling for northward migration at the site.

My results highlight the need for broader habitat conservation measures throughout the range of sandpipers, including lesser-recognized secondary habitats that are being used successfully by birds across their range.

Supervisor: Dr. Diana Hamilton, Professor ~ research website


Linhart, RC, DJ Hamilton, J Paquet, O Monteiro, G Ramires, and J Mobley. 2022. Movement and habitat use of non-breeding Semipalmated Sandpipers (Calidris pusilla) at the Banco dos Cajuais in North Eastern Brazil. Conservation Science and Practice: 2022;e12683.

Recipient of the Governor General's Gold Medal, May 2022, awarded to the graduate student in the graduating class who has the highest average of all those receiving a graduate degree.


Prochlorococcus marinus: Response to light and oxygen ~ Mireille Savoie, MSc (2023)

Abstract: Prochlorococcus marinus are the most abundant photosynthetic organisms, with at least twelve clades, growing in tropical and subtropical oligotrophic oceans. Climate change models predict 10° poleward shifts in phytoplankter ranges, bringing Prochlorococcus marinus into wider variations in photoperiod and spectral regimes. In parallel some Prochlorococcus marinus strains are found in low oxygen zones, which are also expanding with climate change. Using growth determinations under matrices of oxygen concentrations [O2], light levels, spectral wavebands and photoperiods, followed by Generalized Additive Modelling, we analyzed growth responses of 3 representative clades of Prochlorococcus marinus. We found that a near-surface, clade High Light I Prochlorococcus marinus MED4, grows fastest under higher light and longer photoperiods, but is excluded from growth under both 4 h photoperiod, and low [O2] regimes. A deep-water, clade Low Light III Prochlorococcus marinus SS120, grows fastest under low light and longer photoperiods, but can utilize higher light levels and shorter photoperiods when grown under 25 µM of O2. A deep-water, clade Low Light IV Prochlorococcus marinus MIT9313, is excluded from growth under high light combined with full surface [O2], but can exploit higher light levels and longer photoperiods when grown under 2.5 µM and 25 µM of O2. Through this analysis, we defined the interactions between oxygen, light level, spectral colour and photoperiod that help define the complex current and potential future niches of representative strains of Prochlorococcus marinus.

Further investigation of the influence of light quality (spectral waveband) and quantity (light level) on Prochlorococcus marinus growth was achieved by converting the quantity of treatment light levels, the photosynthetically available radiation, to the quantity of light each of our studied clades actually absorbed, the photosynthetically usable radiation. The pigment composition of photosynthetic organisms determines which spectral wavebands are absorbed, thereby consolidating the influence of spectral wavebands. We demonstrate that by collapsing the influence of photoperiod, by expressing the growth response in terms of cumulative diel photosynthetically usable radiation, Prochlorococcus marinus MIT9313 and SS120 showed full growth inhibition across photoperiods and spectral wavebands for cumulative diel photosynthetically usable radiation greater than 1.0 x 106 µmol photons m-2 d-1, when treated with 250 µM of O2. In contrast, Prochlorococcus marinus MED4 exhibited growth saturation at 1.0 x 106 µmol photons m-2 d-1. Expressing growth response in terms of cumulative diel photosynthetically usable radiation simplifies the complex matrix of our treatment conditions, allowing for better insight into possible physiological processes that may be driving the observed growth responses.

Supervisor: Dr. Douglas Campbell, Professor; Canada Research Chair in Phytoplankton Ecophysiology ~ Campbell Phytoplankton Physiology publications

Research Poster Presentations:

Savoie M., Genge L., Śliwińska-Wilczewska S., Berthold M., Omar N., & Campbell DA. (2023)  Are ‘low light’ Prochlorococcus ecotypes high light opportunists under low [O2]? Canadian Society of Microbiology Conference, Halifax, Nova Scotia -  Poster presentation.

Savoie M., Arthur S., Genge L., Berthold M. & Campbell DA. (2022) Prochlorococcus marinus: Growth responses to oxygen; photoperiod; light quality and level. ProSynfest2020 Conference, Cordoba, Spain - Virtual poster presentation.

Awards: Recipient of the Governor General's Gold Medal, May 2024, awarded to the graduate student in the graduating class who has the highest average of all those receiving a graduate degree.

Characterizing nutrient-activation of orphan and lipid metabolism-related G protein-coupled receptors ~ Madeline Power, MSc (2022)

Abstract: Nutrients and food additives serve as energy sources or non-nutritive flavour enhancers for organisms. Advances in nutrient-sensing mechanisms and the discovery of the reciprocal relationship between metabolism and intracellular pathways have identified some nutritive and non-nutritive food components, namely amino acids (AAs) and non-nutritive sweeteners (NNSs), as ligands for G protein-coupled receptors (GPCRs). For example, AAs act as ligands for mGluRs, multiple class C GPCRs and the class A orphans GPR142 and GPR139.

Meanwhile, NNSs of markedly different structures have been shown to activate the sweet taste receptors T1R2/T1R3. The consumption of AAs aids in managing food intake and glucose homeostasis, although the mechanisms underlying these metabolic benefits remain unclear. However, a recent study identified an intestinal trafficking mechanism of individual AAs leading to the activation of an AA-sensing GPCR, suggesting that GPCRs play a larger role in nutrient signalling than once thought. Food products containing NNSs have become increasingly popular over the past few decades to provide powerful sweetness, in part through the activation of T1R2/T1R3, without the added calories. Despite being considered metabolically inert, the consumption of NNSs has been linked to an increased risk of obesity, type 2 diabetes, and metabolic syndrome with suggested off-target signalling through GPCRs independent of T1R2/T1R3.

Ligand identification is critical in understanding GPCR function; as a result, we used a high throughput approach quantifying GPCR activation to identify novel nutrient-GPCR interactions. This approach was applied to two experimental questions 1) to what extent do AAs activate orphan and lipid metabolism-related GPCRs, and 2) do NNSs elicit off-target signalling events through interactions with GPCRs? Both projects primarily measured β-arrestin recruitment and used a panel of in vitro luciferase signalling reporters. Herein, we discovered that the AA L-phenylalanine (Phe) is a promiscuous endogenous ligand, significantly activating 148 class A GPCRs. Additionally, we found that the NNS sucralose increases the activity of the constitutively active orphan GPCR GPR52. These observations are the first to identify the widespread binding capacity of Phe through GPCRs and a GPCR other than the taste receptors as a target for sucralose. This study provides evidence of the interplay between metabolite sensing and the GPCR signalling network and may potentially inform pharmacological approaches to predict novel agonists or off-target effects.

Supervisor: Dr. Jill Rourke, Assistant Professor ~ Rourke Lab

Exploring the molecular promiscuity of L-Phenylalanine (Phe) activation of G protein-coupled receptors, 21st Great Lakes GPCR Retreat (2022), trainee poster presentation and selected for oral presentation.

2022 Senior Women Academic Administrators of Canada (SWAAC) Graduate Student Award of Merit. Awarded to women registered in Masters or PhD programs at any Canadian University who demonstrate outstanding academic performance and leadership.

The non-nutritive sweetener (NNS) sucralose activates an orphan G protein-coupled receptor (GPCRs), Canadian Society of Pharmacology and Therapeutics Annual Scientific Meeting (2021), trainee poster presentation. Published abstract: Power, M; Fernandez N; MacKinnon, B; Rourke J. 2021. Canadian Journal of Physiology and Pharmacology. Canadian Society of Pharmacology and Therapeutics annual conference, Canada (S10). Canadian Science Publishing, Canada.

Exploring the molecular promiscuity of L-Phenylalanine activation of G protein-coupled receptors, New Brunswick Health Research Foundation Health Research Week (2021), Master’s poster presentation

L’acide amine L-phénylalanine active les récepteurs couplés aux protéines G (RCPG) orphelins de la class A, Le 31e colloque des jeunes chercheuses et chercheurs Université de Moncton (2021), poster presentation finalist.

L-phenylalanine activates class A orphan G protein-coupled receptors, New Brunswick Health Research Foundation Health Research Week (2020), Master’s poster presentation finalist and selected for oral presentation.

Recipient of the Governor General's Gold Medal, May 2023, awarded to the graduate student in the graduating class who has the highest average of all those receiving a graduate degree.

Reactive Oxygen Species Production and Scavenging; Genomic Patterns Across Marine Phytoplankton ~ Naaman Omar, MSc (2022)

Abstract: Marine phytoplankton produce and scavenge Reactive Oxygen Species (ROS), to maintain intracellular ROS homeostasis to support cellular processes, but limit damaging reactions.  Some prokaryotic picophytoplankton have lost genes encoding the capacity to scavenge Hydrogen Peroxide (H2O2). The “Black Queen Hypothesis” postulates that prokaryotic picophytoplankton might thereby lower costs through H2O2 diffusing across the membrane of the small source cells.

We investigated genomes and transcriptomes from diverse taxonomic lineages of eukaryotic phytoplankton, ranging from 0.4 to 44 µm cell radius, to analyze the fraction of total genes dedicated to producing enzymes metabolizing three distinct ROS.

H2O2 has low reactivity, long intracellular and extracellular lifetimes and readily crosses cell membranes, and can therefore potentially leave a cell before provoking damaging intracellular reactions.  Across eukaryotic phytoplankton, the fraction of total genes dedicated to H2O2 production indeed decreases with increasing cell radius, consistent with the maintenance of ROS homeostasis in the face of slower diffusional losses of H2O2.  The fraction of total genes dedicated to H2O2 scavenging does not change with increasing cell radius, although taxonomic lineage influences the fraction of total genes dedicated to H2O2 metabolism.

Superoxide (O
) has high reactivity, short intracellular and extracellular lifetimes, and limited membrane permeability. As expected, genes encoding O
scavenging were ubiquitous, and did not change with radius, consistent with separate intracellular and extracellular O
pools separated by the cell membrane.

Nitric Oxide (•NO) has low reactivity, long intracellular and extracellular lifetimes, and readily crosses cell membranes. Neither •NO production nor scavenging genomic capacities changed with increasing cell radius, but were influenced by taxonomic lineage, consistent with the low cytotoxicity and diverse regulatory roles of •NO.

Supervisor:  Dr. Douglas Campbell, Professor; Canada Research Chair in Phytoplankton Ecophysiology ~ Campbell Phytoplankton Physiology publications

Naaman M Omar, Ondřej Prášil, J Scott P McCain, Douglas A Campbell. 2022.  Diffusional Interactions among Marine Phytoplankton and Bacterioplankton: Modelling H2O2 as a Case Study  Microorganisms 10(4), 821