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Abstract: It has been established that taurine, an important osmolyte in the cellular deswelling process, is critical for brook char (Salvelinus fontinalis) to achieve maximum cardiac function when faced with physiological and environmental stressors. This study aimed to better understand whole animal physiology when fish are taurine deficient, as well as determine blood pressure and intrinsic heart rate through intravascular cannulation. Various tissues were used to investigate the enzymatic activity of cysteine dioxygenase (CDO), a key enzyme in the production of intracellular taurine, based on the assumption that fish might be able to upregulate taurine production if taurine deficient. Lastly, we attempted to create a novel investigative method to determine taurine excretion via bile acids in fish plasma. We generated a taurine-deficient brook char model using a feed enriched with 5% β-alanine to inhibit cellular taurine uptake. Fish behaviour was found to not significantly differ, although it is suspected this may be due to tank isolation and lack of social interaction. No differences in metabolic demands were observed, and cortisol levels indicated the fish were not stressed. In control fish, intrinsic heart rate (IHR) was found to be less than taurine deficient fish, although this was not significantly different. Control fish exhibited an unexpected downward trend in IHR compared to TD who exhibited the typical upwards trend in IHR. Liver was found to produce the most cysteine sulfinic acid and cysteic acid, while CDO in heart tissue had the highest enzymatic rate. However, control heart CDO was significantly more active than taurine deficient heart CDO. The most abundant bile acid was taurocholic acid, with the other bile acids being under the limit of detection. An unexplored role of taurine conjugates acting as the primary molecule in enterohepatic circulation was seen as well. Overall, taurine appears to play a key role in supporting respiration, however, brook char do not seem to be able to upregulate CDO, indicating that as the nutritional landscape changes with climate change, wild fish could become taurine deficient and experience higher rates of cardiac failure.

Supervisor: Dr. Tyson MacCormack, Professor ~

Abstract: Hypoxia is a growing concern, with events becoming more prevalent, severe, and frequent. Organisms must adapt or face mortality, employing strategies such as avoiding hypoxic zones, decreasing metabolic requirements, or switching mitochondrial substrates. Teleost fish, the most recent evolutionary fish taxa, oxidize glucose and lipids under normoxia. However, these substrates can become limiting or damaging under hypoxia due to ROS. Ketone bodies offer an alternative substrate. In mammals, ketones are beneficial, but little is known about ketosis in fish. Elasmobranchs, appearing ~400 million years ago, preferentially oxidize ketone bodies and evolved through hypoxia. Acipenseriformes, appearing ~200 million years ago, also oxidize ketone bodies, and teleosts are assumed to lack this ability.

Since Zammit and Newsholme (1979), interest in ketone bodies in fish, other than elasmobranchs, has diminished. We hypothesize that ketosis evolved in elasmobranchs to mitigate hypoxic consequences. We further hypothesized that species from these taxa would exhibit a beneficial whole-animal ketogenic response to hypoxia. To test this, we subjected an elasmobranch, an acipenseriform, and a teleost to acute and chronic hypoxia. Species decreased their metabolic rate in response to hypoxia in a lab setting, which seemed sufficient to avoid hypoxic consequences but is not ideal in nature.

Though we did not observe a ketogenic response in these species, we gained valuable insights into the hypoxic response of evolutionarily distinct fish. This study was among the first to compare mitochondrial metabolism between ketone bodies and pyruvate and to demonstrate that teleost fish can oxidize ketones as a meaningful respiratory substrate.

Supervisor: Dr. Andrea Morash, Associate Professor

Abstract: Each year, shorebirds use staging sites in Atlantic Canada during their fall migration to southern wintering grounds. As shorebird populations of many species are in decline throughout their range, research on habitat availability and use is necessary to inform conservation action. This research had two main objectives. First, I studied late-season migrants to determine if there is a relationship between migratory distance, timing and staging strategy. Second, I examined whether we could use in situ sampling and remote sensing to predict shorebird abundance. To address the first objective, I used the Motus Wildlife Tracking System network to track movements of Semipalmated Sandpipers (SESA) (Calidris pusilla) and three late-season migrants: White-rumped Sandpipers (WRSA) (Calidris fuscicollis), Sanderling (SAND) (Calidris alba), and Dunlin (DUNL) (Calidris alpina) in Atlantic Canada to determine length of stay, regional daily movements, and departure conditions. I coupled this with an analysis of plasma triglycerides and stable isotopes of carbon and nitrogen in blood plasma to determine short-term metabolic state and dietary niches respectively. I found that WRSA, the longest distance migrants, had a shorter length of stay, frequent regional movement, higher relative fuel loads, and plasma triglycerides, and were less selective of optimal weather conditions upon departure. Conversely, DUNL, which migrate the shortest distance, had longer stopover duration, reduced movement, lower relative fuel loads and were selective of optimal wind conditions. DUNL, WRSA and SESA had overlapping dietary niches, whereas the diet of SAND consisted of more terrestrial based prey. For the second objective, I conducted invertebrate and sediment sampling coupled with shorebird surveys at 10 sites along the Northumberland Strait. Additionally, I used Sentinel-2 satellite imagery to extract surface reflectance values at each site. Together these data were used to investigate relationships between shorebird abundance and both habitat and spectral properties. I found correlations between shorebird abundance and habitat characteristics, surface reflectance and habitat characteristics, and rough relationships between shorebird abundance and reflectance in the near infrared (NIR) and visible Sentinel-2 satellite bands regions. These relationships were then used to create maps to visualize habitat suitability across the sites. Our research fills a knowledge gap of three understudied species in the region as well as contributing to characterization of intertidal habitats in Atlantic Canada for staging shorebirds.

Supervisor: Dr. Diana Hamilton, Professor ~

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 ~

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 ~

Presentation:

"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.

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 5-9^oC 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 19-24^oC 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 27^oC). I found that Atlantic salmon grew at similar rates at 16-21 and 19-24^oC as parr, but smolts grew slower at 19-24^oC 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 (24^oC) 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 27^oC exposure which also increased some reflex impairments predicting greater post-angling mortality. T_max may thus be an important factor to consider in closing/opening recreational fisheries which have considered some river temperature parameters.

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

Presentations:

“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.

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 ~

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: 

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 ~

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

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 ~ ~ and Dr. Myriam Barbeau

Publications/News:
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.

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 ~

Publications/News:

Linhart, RC, DJ Hamilton, J Paquet, O Monteiro, G Ramires, and J Mobley. 2022. . 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.

Abstract: Exercise is an integral part of human existence with great benefits including social wellness, mental health, and the well-being of many organs of the body. Recent reports show that lactoylation of the amino acid phenylalanine (Phe) produces the exerkine N-lactoyl-phenylalanine (Lac-Phe), which increases during exercise in rodents and humans and serves as an appetite suppressant, protecting against obesity. Extracellular Lac-Phe levels positively correlate with lactate production and high Phe in PKU (Phenylketonuria) and are also of interest in diabetes, cancer, and cardiac disease. However, nothing is known about the cellular target of Lac-Phe bioactivity. This study hypothesizes that Lac-Phe might be signaling through the abundant GPCRs to produce reported effects. To test this, we quantified the activation of 298 GPCRs in the presence of Lac-Phe treatments which produces a concentration-dependent activation of five receptor candidates (GPR3, GPR4, GPR6, GPR12, and MAS1) with fold change range of 2.424 - 3.959 fold (95% CI; 1.370 – 4.699) and half maximal effective concentration (EC50) range of 31 - 327 µM (95% CI; 16 – 624 µM), aligning with a putative paracrine mode of action. The signaling is specific to Lac-Phe, sensitive to medium conditions, and also β-arrestin biased when tested in downstream cAMP and MAPK pathways. With the growing interest in Lac-Phe and its reported links to metabolic disorders, this study presents some novel information behind the bioactivity of LacPhe as an exerkine through GPCR signaling. Our findings suggest that Lac-Phe is a promising signaling metabolite with GPCR targeting options that warrant further pharmacological characterization.

Supervisor: Dr. Jill Rourke, Assistant Professor ~

Publications/Presentations/Awards:

Cahill, H.F, Scott, B., Oni, O.P, Stapleton, G., MacCormack, T., Meli, V., Rourke, J.L. (2024) Multiparametric cytotoxicity profiling reveals cell-line and ligand-dependent toxicity for pegylated gold nanoparticles (AuNP-PEG). Canadian Journal of Chemistry 102(3): 134-143. 
 
Power, M. E., Fernandez, N. R., Oni, O. P,. A., Kalia, A. N., & Rourke, J. L. (2024). The non-nutritive sweetener sucralose increases β-arrestin signaling at the constitutively active orphan G protein-coupled receptor GPR52. (2023) Canadian Journal of Physiology and Pharmacology 102(2): 116-127.
 
Oni, O. P., McCardle I.C., Rourke, J.L., A new signalling metabolite? Characterizing N-Lactotyl-phenylalanine (Lac-Phe) activation of G protein-coupled receptors. 2023 Proceedings of Research News Brunswick Health Research Week, NB, Canada. Nov. 16 -17 2023 (Oral Presentation)

Oni, O. P., McCardle I.C., Rourke, J.L., A new signalling metabolite? Characterizing N-Lactotyl-phenylalanine (Lac-Phe) activation of G protein-coupled receptors. 22nd Annual Great Lakes G Protein-Coupled Receptor Retreat, Quebec, Canada. Nov. 2-4 2023 (Poster Presentation)

Oni, O.P., Power, M., Rourke J.L., Exploring the molecular promiscuity of L-phenylalanine (Phe) activation of G protein-coupled receptors. 2023 Maritimes Biological Chemistry Conference, Halifax, Canada August 28th -30th 2023 (Oral Presentation)

Oni, O.P., Power, M., Rourke J.L., Exploring the molecular promiscuity of L-phenylalanine (Phe) activation of G protein-coupled receptors. 2023 Annual Meeting of Canadian Society of Pharmacology and Therapeutics. June 6th -7th  2023 (Oral Presentation)

Oni, O.P., Power, M., Rourke J.L., Exploring the molecular promiscuity of L-phenylalanine (Phe) activation of G protein-coupled receptors. 65th Annual Conference of Canadian Society for Molecular Biosciences (CSMB) Ottawa Canada, May 30th – June 2nd 2023 (Poster Presentation)
 
Trainee Top 10 abstracts -- 2023 Annual Meeting of Canadian Society of Pharmacology and Therapeutics – June 2023

2023 Maritimes Biological Chemistry Conference Oral Presentation Winner (MSc Category) –  August 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 ~

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 / News:

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.

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 ~
 
Presentations/Publications/Awards:

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) . 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. , 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.

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⁻
₂) has high reactivity, short intracellular and extracellular lifetimes, and limited membrane permeability. As expected, genes encoding O⁻
₂ scavenging were ubiquitous, and did not change with radius, consistent with separate intracellular and extracellular O⁻
₂ 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 ~

Publications/News:
Naaman M Omar, Ondřej Prášil, J Scott P McCain, Douglas A Campbell. 2022.    Microorganisms 10(4), 821