France

Energy metabolism (encompassing energy assimilation, conversion and utilization) plays a central role in all life processes and serves as a link between the organismal physiology, behavior, and ecology. Metabolic rates define the physiological and life-history performance of an organism and have direct implications for Darwinian fitness. Anthropogenic and natural stressors affect energy balance because the stress-induced disruption of homeostasis must be corrected to ensure the organism&#39;s survival. Pollutants can negatively affect different aspects of energy metabolism of an organism interfering with energy assimilation and conversion or increasing energy costs for basal maintenance. This can diminish the energy fluxes available for other fitness functions and negatively affect the organism’s growth, reproduction and ability to deal with additional stressors or diseases. In this talk, I will discuss the role of bioenergetics in toxicity of legacy and emerging pollutants (including trace metals, nanoparticles and pharmaceuticals) and the pollutant interactions with other abiotic stressors such as temperature, salinity or oxygen deficiency. I will address the mechanisms underlying the pollutant-induced bioenergetics disturbances and discuss the use of bioenergetics-based approaches in linking the molecular and cellular stress responses to the whole-organism fitness in coastal environments exposed to multiple stressors.

SEB Annual Conference 2022

Bioenergetic aspects of pollutant toxicity and their role in determining the tolerance limits to multiple stressors in aquatic organisms

Energy metabolism (encompassing energy assimilation, conversion and utilization) plays a central role in all life processes and serves as a link between the organismal physiology, behavior, and ecology. Metabolic rates define the physiological and life-history performance of an organism and have direct implications for Darwinian fitness. Anthropogenic and natural stressors affect energy balance because the stress-induced disruption of homeostasis must be corrected to ensure the organism's survival. Pollutants can negatively affect different aspects of energy metabolism of an organism interfering with energy assimilation and conversion or increasing energy costs for basal maintenance. This can diminish the energy fluxes available for other fitness functions and negatively affect the organism’s growth, reproduction and ability to deal with additional stressors or diseases. In this talk, I will discuss the role of bioenergetics in toxicity of legacy and emerging pollutants (including trace metals, nanoparticles and pharmaceuticals) and the pollutant interactions with other abiotic stressors such as temperature, salinity or oxygen deficiency. I will address the mechanisms underlying the pollutant-induced bioenergetics disturbances and discuss the use of bioenergetics-based approaches in linking the molecular and cellular stress responses to the whole-organism fitness in coastal environments exposed to multiple stressors.

technical paper

Discover the art of creating extraordinary science at SEB’s Annual Conference at Le Corum Conference Center     in Montpellier, France from 5 to  8 July 2022.

SEB’s Annual Conference is celebrated for creating the perfect composition of research, new discoveries and collaborative connections. Be creative and innovative by exchanging ideas and knowledge with masters of biology from all over the world.

2022 will find over 1500 experimental biologists from across the globe converging on the third-largest French city near the Mediterranean coast and the fastest-growing city in the country over the past 25 years.
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2022 will find over 1500 experimental biologists from across the globe converging on the third-largest French city near the Mediterranean coast and the fastest-growing city in the country over the past 25 years - Montpellier, France

We study the potential of a recent invader, the Asian brush-clawed crab (Hemigrapsus takanoi), to expand its distribution range further into the Baltic Sea. H. takanoi has been documented in the southwestern Baltic Sea since 2014. The ability to persist and further expand into the Baltic Sea will depend on their potential to sustain all stages of their complex life cycle, including pelagic larvae, under the Baltic Sea’s conditions. Range limits may be established by the tolerance to low salinity, which in addition may be affected by temperature. A key question is whether local populations at the distribution limit (within the Baltic) are adapting to low salinities and hence promote further expansion. We quantified the combined effects of salinity (10-32 PSU) and temperature (15-24°C) on four populations of H. takanoi (two from the Baltic and two from the North Sea). Our results show substantial differences in larval performance between the populations from the Baltic and North Sea. Larvae from the North Sea populations show higher survival and faster development compared with those from the Baltic Sea. No evidence of elevated tolerance towards low salinity were found in the larvae from the Baltic Sea. In addition, larvae from the population located at the range limit (Neustadt) show very low survival. We did not find evidence of adaptation to low salinity by any of the local populations of H. takanoi we studied. Thus, in order to the population to persist, larvae must either migrate to waters of increased salinity, and then return to the habitat of origin; or such populations are sustained by source-sink dynamics. 


Living at the frontier - salinity and temperature during larval development determine the potential for invasion of the Baltic Sea

Evolution as a contemporary process that can affect changes from one generation to the next has only recently been considered in toxicology. While rapid evolution has recently been linked with the increase of invasive capacity of Invasive Alien Species (IAS), it is still not taken into consideration for Invasive Species Predictive Schemes and risk assessments. 
The Louisiana crayfish, Procambarus clarkii, has a strong adaptive capacity to a variety of aquatic environments, including highly contaminated water bodies, and different salinities. Here, we studied three invasive populations of P. clarkii that inhabit water bodies at different salinities and pollution levels in the South of France. Our results showed that physiological and molecular responses are population-specific when they are exposed to pollutants and salinity shock. Our results suggest that in P. clarkii, the capacity to inhabit polluted environments and the capacity to inhabit water bodies with different salinity levels are not related. While the capacity to face pollutants seems to share a common ancestor in these three populations, the capacity of dealing with salinity change seems to be a more recently acquired trial.

Physiological and molecular responses of P. clarkii to different levels of pollutants and salinity exposure: an Interpopulation study.

Nonpollinating fig wasps (Hymenoptera: Chalcidoidea) are the most remarkable exploiters of the Ficus (Moraceae) and pollinating fig wasp (Hymenoptera: Agaonidae) mutualism. Both pollinating and nonpollinating fig wasps lay their eggs inside the inflorescences of the fig trees (Ficus), where their larvae grow. The nonpollinating fig wasps (NPFWs) negatively impact the pollinator population and fig seed production because, for each NPFW hatch in a fig, a pollinator or a seed has been terminated. Moreover, NPFWs can kill all the pollinating males in a fig and doom all the wasps in a single fig, as pollinating males dig the exit hole out of a fig. Up to now, only experimental studies based on the absence/presence of NPFWs have been done. To better quantify the impact of NPFWs, we conducted bagging experiments using a controlled number of fig wasps. Pollinating wasps were introduced in bags containing receptive figs and different numbers of NPFWs (from none to five). For this experiment, we used the pollinating wasp, Ceratosolen wui, and the NPFW species, Philotrypesis taida living on the fig tree Ficus benguetensis in Northern Taiwan. We found that higher numbers of NPFWs increased the fig abortion rate before maturation and decreased the number of emerging wasps and the proportion of pollinators. In conclusion, we suggest that selective abortion in the early stage of fig development is a density-dependent defense mechanism against NPFWs.

Fig abortion as a defense mechanism for Ficus trees and pollinating fig wasps

The cellular adaptive response is a defense network that allows cells to survive and proliferate in the presence of stressful factors. These stressors, which include hypoxia, radiation, thermal shock, and heavy metals, damage cells by increasing oxidative stress via increased generation of reactive oxygen species (ROS). The exposure to mild stress (e.g. thermal shock of 40°C) for an extended period can activate the cellular adaptive response and protect the cell against subsequent exposures to lethal stress doses (e.g. lethal thermal shock of 42°C). However, the mechanisms by which this response is activated are still poorly understood. Nrf2, a transcription factor found as a cytosolic heterodimer with Keap1, is activated in response to oxidative stress and translocates to the nucleus where it binds to the antioxidant response element and initiates a host of antioxidant defenses. The role of Nrf2 in the cellular adaptive response is of the utmost importance. Our studies seek to understand 1) ROS generation in response to mild heat stress, 2) how these increased ROS modulate activation of the cellular adaptive response, and 3) the role of Nrf2 in the modulation of ROS generation and activation of the cellular adaptive response. Our results in HeLa cells show that increased ROS at 40°C originate from both mitochondria and NADPH oxidase. Modulation of Nrf2 activity via overexpressor and knockdown cell lines significantly impacts ROS generation during mild heat stress. Elucidating the role of ROS in the establishment of the cellular adaptive response paves the way to new potential therapeutic treatments.

Oxidative stress induced by mild heat shock at 40°C activates a cell survival response modulated by Nrf2

We demonstrate that one-pot consolidated bioprocessing using deep eutectic solvents can improve the extraction of fermentable sugars from the green seaweed, Ulva linza. Ulva biomass was first pretreated with either sulfuric acid, the deep eutectic solvent choline chloride-oxalic acid, or the ionic liquid 1-ethyl-3-methylimidazolium bromide. After pretreatment, we separated solubilised sugars from residual solids. The residual solids were saccharified using green solvent-stable glycosidases that were isolated from a newly identified strain of the ascomycetous fungus, Penicillium oxalicum. The factors affecting this saccharification were quantified from the response surfaces of a Box-Behnken design. Finally, the sugars extracted from Ulva biomass were fermented into bioethanol using a dual yeast culture. We obtained higher bioethanol yields from Ulva biomass with consolidated processing in deep eutectic solvents, compared to lower yields from Ulva biomass with other solvents or two-stage processing.

One-pot processing of Ulva seaweed biomass with deep eutectic solvent-optimized fermentation

The evolution of lignification in vascular plants conferred improved structural support, defence, and water transport, improving the success of plants on land. Despite lignification being a land plant specific expansion, lignin-like compounds have been identified in the cell walls of intertidal seaweeds. Here, I aim to characterise the function and structure of the ‘phycolignin’ fraction of the chlorophyte seaweed Ulva compressa. UV excitation of Ulva cell wall autofluorescence using confocal microscopy induced a blue-green emission profile comparable to that of lignin, which was significantly elevated under hyposaline stress (1.7X fold change to control, ***) and significantly reduced under hypersaline stress (0.5X fold change, ***), indicating a possible osmoprotective role. Cell walls were then isolated and fractionated into pectin, hemicellulose, and ⍺-cellulose to identify this fluorophore, with plant biomass also fractionated as a ‘lignin positive’ control. Several biochemical tests were performed to identify which polysaccharides lignin-like structures were associated with, followed by ATR-FTIR and NMR. ‘Phycolignin’ in Ulva appeared to be associated with cellulose and hemicellulose, with potential aromatic groups identified by ATR-FTIR and 1H NMR (solution-state). Positive identification of lignin within plant extracts showed that Ulva ‘phycolignin’ displayed fundamental structural differences to true lignin. However, the lack of available reference spectra for FTIR of chlorophyte phenolics, and the general insolubility of the Ulva cell wall in conventional NMR solvents limited data interpretation. Better structural characterisation of ‘phycolignin’ in Ulva will increase our understanding on how multicellularity, the metabolome, and stress responses evolved and diverge within the green lineage.

Characterisation of 'phycolignin' in the cell wall of chlorophyte seaweeds

Mitochondria possess a genome, a vestige of their bacterial ancestor. Over the course of evolution, most of the genes of the ancestor have been lost or transferred to the nucleus. In humans, the mtDNA is limited to 37 genes, with little room for evolutionary novelties. This is radically different from bacterial genomes, which are much larger, and in which we can find genes inside other genes. These sequences are called alternatives open reading frames or altORFs, and they have key functions. By ignoring altORFS, have we underestimated the coding potential of the mitogenome? We found a downstream alternative ATG initiation codon in the +3 reading frame of the human mitochondrial nd4 gene. This newly characterized mitochondrial altORF encodes a 99-amino acids long polypeptide termed MTALTND4 with a completely different amino acid sequence from ND4. MTALTND4 is localized in mitochondria and is also found in the plasma, and it impacts mitochondrial physiology. These findings indicate that mitochondrial genes in humans (and other species) have gone unnoticed. This calls into question the evolution of the mitochondrial genome as well as the selection pressures exerted on the mitochondria and the mechanisms allowing the translation of these alternative proteins. We anticipate that more studies on the alternative mitochondrial proteome will expedite the discovery of new mitochondrial genes with key biological roles.

The underestimated protein coding potential of the mitochondrial genome

Birds metabolically remodel their flight muscle prior to migration to meet the high energetic demands of migratory flight. The degree of plasticity mediated by changes in mitochondrial function is poorly understood but could be explained by two non-mutually exclusive hypotheses: variation in mitochondrial quantity or individual mitochondrial function. For each hypothesis, we predicted higher mitochondrial abundance and predict higher substrate oxidative capacity and reduced reactive oxygen species formation during migration, respectively. We evaluated both hypotheses using yellow-rumped warblers (Setophaga coronata) captured during their autumn migration at Long Point, Ontario, Canada. Half of the birds were sampled in the migratory phenotype and the remaining birds were transferred to a short day photoperiod (9L:15D) and sampled in a non-migratory phenotype. We measured mitochondrial abundance via citrate synthase maximal activity in the pectoralis major flight muscle. We investigated mitochondrial function via high-resolution fluororespirometry on isolated pectoralis mitochondria. We measured O2 consumption and H2O2 formation rates from oxidation of lipid and carbohydrate substrates. We also measured oxygen consumption specific to electron transport system protein complexes using complex-specific substrates and inhibitors. Citrate synthase activity and mitochondrial respiration for each substrate and complexes II, III and IV was higher in the migratory phenotype, yet H2O2 formation rates were similar between phenotypes. These data suggest that pectoralis mitochondrial abundance and oxidative capacity are elevated during migration without increasing reactive oxygen species formation. Our findings support both hypotheses and indicate that mitochondrial function mediates seasonal metabolic plasticity in the pectoralis flight muscle of migratory songbirds.

Flight muscle mitochondria are seasonally plastic in a migratory songbird

Mandibular kinetics and associated occlusal relations have been a significant focus of physiological studies of mammalian mastication. However, soft tissue deformations of the masticatory apparatus are essential to mastication. Whereas the jaw muscles, ligaments and temporomandibular joint (TMJ) articular disc are vital for jaw movements, perioral muscles and the tongue are key to bolus management and transport. We synthesize deformations of these soft tissue structures as the jaw moves during chewing and propose future avenues of research investigating soft tissue dynamics during mastication. Jaw muscles shorten 5-10% and cheek muscles over 15% during mastication, and their bulging creates pressure on adjacent bones and ligaments. Muscle contraction moves and loads the TMJ, causing the disc and capsule to elongate anteroposteriorly during jaw closing. During jaw opening, muscles lengthen, stretching aponeuroses 4-5%. Chewing side, food hardness, regional and individual differences all modify these effects. The most important soft tissue for mammalian mastication is, however, the tongue, and it undergoes the largest deformations. There are differences in how various species use the tongue during mastication, but all species examined exhibit regional complexity in the amplitude and timing relative to jaw movements. In pigs, for example, the anterior tongue lengthens as the jaw closes, reaching maximum length around minimum gape, then quickly shortens as jaw opening begins. Posterior regions lengthen during jaw closing and opening but shorten much later during opening. Synthesizing these functional roles emphasizes the significance of soft tissue mechanics in masticatory performance.

No Bones About It: Soft Tissue Dynamics during Mammalian Mastication

Jaw movements during mammalian chewing drive occlusion and food breakdown. As important as jaw movements are for chewing, soft tissues within the oral cavity are essential for handling the food bolus throughout the chewing sequence. For instance, tongue movements and deformations (1) position the food between the tooth rows, (2) help mix the bolus with saliva to initiate digestion and improve swallowability, and (3) transport the bolus to the oropharynx to initiate the swallow. Tongue movements and deformations must be coordinated with jaw movements to ensure chewing performance and efficiency as well as to avoid self-injury, and previous research shows that disruption of the sensory input from the tongue alters jaw movements during chewing in pigs. Even though jaw and tongue movements during mammalian chewing are investigated extensively, their coordination pattern(s) have received less attention. We present three different approaches to quantify the correlation between jaw movements (opening and closing, mediolateral deviation) and tongue movements (positional changes such as protraction-retraction) and deformation (length and width changes) during chewing in pigs. At the sequence level, cross-correlations are used to calculate the lag in time between tongue and jaw kinematics. Cross-correlation analyses can also be carried out at the cycle level, albeit with less statistical power. Finally, functional data analysis standardizes and resamples the data to test for jaw-tongue correlation at each time point, essentially testing bivariate correlation continuously throughout the chewing cycle. We discuss the benefits and limitations of each methodology to emphasize the impact of combining analytical tools.

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