Posts Tagged 'molecular biology'

DNA damage and oxidative stress responses of mussels Mytilus galloprovincialis to paralytic shellfish toxins under warming and acidification conditions – elucidation on the organ-specificity

Commonly affected by changes in climate and environmental conditions, coastal areas are very dynamic environments where shellfish play an important ecological role. In this study, the oxidative stress and genotoxic responses of mussels (Mytilus galloprovincialis) exposed to paralytic shellfish toxin (PST) – producing dinoflagellates Gymnodinium catenatum were evaluated under i) current conditions (CC: 19 °C; pH 8.0), ii) warming (W: 24 °C; pH 8.0), iii) acidification (A:19 °C; pH 7.6) and iv) combined effect of warming and acidification (WA: 24 °C; pH 7.6). Mussels were fed with G. catenatum for 5 days, and to a non-toxic diet during the following 10 days. A battery of oxidative stress biomarkers and comet assay was performed at the peak of toxin accumulation and at the end of the post-exposure phase. Under CC, gills and hepatopancreas displayed different responses/vulnerabilities and mechanisms to cope with PST. While gills presented a tendency for lipid peroxidation (LPO) and genetic damage (expressed by the Genetic Damage Indicator – GDI), hepatopancreas seems to better cope with the toxins, as no LPO was observed. However, the mechanisms involved in hepatopancreas protection were not enough to maintain DNA integrity. The absence of LPO, and the antioxidant system low responsiveness, suggests DNA damage was not oxidative. When exposed to toxic algae under W, toxin-modulated antioxidant responses were observed in both gills and hepatopancreas. Simultaneous exposure to the stressors highlighted gills susceptibility with a synergistic interaction increasing DNA damage. Exposure to toxic algae under A led to genotoxicity potentiation in both organs. The combined effect of WA did not cause relevant interactions in gills antioxidant responses, but stressors interactions impacted LPO and GDI. Antioxidant responses and LPO pointed out to be modulated by the environmental conditions in hepatopancreas, while GDI results support the dominance of toxin-triggered process. Overall, these results reveal that simultaneous exposure to warming, acidification and PSTs impairs mussel DNA integrity, compromising the genetic information due to the synergetic effects. Finally, this study highlights the increasing ecological risk of harmful algal blooms to Mytilus galloprovinciallis populations.

Continue reading ‘DNA damage and oxidative stress responses of mussels Mytilus galloprovincialis to paralytic shellfish toxins under warming and acidification conditions – elucidation on the organ-specificity’

DNA methylation changes in response to ocean acidification at the time of larval metamorphosis in the edible oyster, Crassostrea hongkongensis

Highlights

  • Low pH stress resulted in hyper- and hypo-methylated genes in the pediveliger larvae of the Hong Kong oyster
  • Differentially methylated loci were concentrated in the exon region within the gene bodies
  • High capability of oyster larvae to acclimate and adapt to low pH condition within single generation despite poor habitat selection for attachment
  • Differential methylation is associated to higher metamorphosis success rate and poor larval substratum selection under low pH stress.

Abstract

Unprecedented rate of increased CO2 level in the ocean and the subsequent changes in carbonate system including decreased pH, known as ocean acidification (OA), is predicted to disrupt not only the calcification process but also several other physiological and developmental processes in a variety of marine organisms, including edible oysters. Nonetheless, not all species are vulnerable to those OA threats, e.g. some species may be able to cope with OA stress using environmentally induced modifications on gene and protein expressions. For example, external environmental stressors including OA can influence the addition and removal of methyl groups through epigenetic modification (e.g. DNA methylation) process to turn gene expression “on or off” as part of a rapid adaptive mechanism to cope with OA. In this study, we tested the above hypothesis through testing the effect of OA, using decreased pH 7.4 as proxy, on DNA methylation pattern of an endemic and a commercially important estuary oyster species, Crassostrea hongkongensis at the time of larval habitat selection and metamorphosis. Larval growth rate did not differ between control pH 8.1 and treatment pH 7.4. The metamorphosis rate of the pediveliger larvae was higher at pH 7.4 than those in control pH 8.1, however over one-third of the larvae raised at pH 7.4 failed to attach on optimal substrate as defined by biofilm presence. During larval development, a total of 130 genes were differentially methylated across the two treatments. The differential methylation in the larval genes may have partially accounted for the higher metamorphosis success rate under decreased pH 7.4 but with poor substratum selection ability. Differentially methylated loci were concentrated in the exon regions and appear to be associated with cytoskeletal and signal transduction, oxidative stress, metabolic processes, and larval metamorphosis, which implies the high potential of C. hongkongensis larvae to acclimate and adapt through non-genetic ways to OA threats within a single generation.

Continue reading ‘DNA methylation changes in response to ocean acidification at the time of larval metamorphosis in the edible oyster, Crassostrea hongkongensis’

Effects of ocean acidification and microplastics on microflora community composition in the digestive tract of the thick shell mussel Mytilus coruscus through 16s RNA gene sequencing

Ocean acidification and microplastic pollution is a global environmental threat, this research evaluated the effects of ocean acidification and microplastics on mussel digestive tract microbial community. The 16S rRNA gene was sequenced to characterize the flora. Species diversity in the samples was assessed by clustering valid tags on 97% similarity. Bacteroidetes, Firmicutes and Proteobacteria were the three most abundant genera in the four groups, with Bacteroidetes showing the highest diversity. However, no differences in flora structure were evident under various treatments. Phylogenetic relationship analysis revealed Bacteroidetes and Firmicutes had the highest OTU diversity. The weighted UniFrac distance, principal coordinate analysis (PCoA), unweighted pair group method with arithmetic mean (UPGMA) cluster tree and analysis of molecular variance (AMOVA) evaluation results for all samples also showed that changes in pH and microplastics concentration did not significantly affect the microbial community structure in the mussel digestive tract. The results presented the no significant effects of ocean acidification and microplastics intake on mussel intestinal diversity.

Continue reading ‘Effects of ocean acidification and microplastics on microflora community composition in the digestive tract of the thick shell mussel Mytilus coruscus through 16s RNA gene sequencing’

Elevated CO2 affects kelp nutrient quality: a case study of Saccharina japonica from CO2 enriched coastal mesocosm systems

Kelps provide critical services for coastal food chains and ecosystem, and they are important food source for some segments of human population. Despite their ecological importance, little is known about long‐term impacts of elevated CO2 (eCO2) on nutrient metabolites in kelps and the underlying regulation mechanisms. In this study, the kelp Saccharina japonica was cultured in CO2 enriched coastal mesocosm systems for up to 3 months. We found that though eCO2 significantly increased the growth rate, carbon concentrations and C/N ratio of S. japonica, it had no effect on total nitrogen and protein contents at the end of cultivation period. Meanwhile it decreased the lipid, magnesium, sodium, calcium contents and changed the amino acid and fatty acid composition. Combining the genome‐wide transcriptomic and metabolic evidence, we obtained a systems‐level understanding of metabolic response of S. japonica to eCO2. The unique ornithine‐urea cycle (OUC) and aspartate‐argininosuccinate shunt (AAS), coupled with TCA cycle balanced the carbon and nitrogen metabolism under eCO2 by providing carbon skeleton for amino acid synthesis and reduced power for nitrogen assimilation. This research provides a major advance in the understanding of kelp nutrient metabolic mechanism in the context of global climate change, and such CO2‐induced shifts in nutritional value may induce changes in the structure and stability of marine trophic webs and affect the quality of human nutrition resources.

Continue reading ‘Elevated CO2 affects kelp nutrient quality: a case study of Saccharina japonica from CO2 enriched coastal mesocosm systems’

Intracellular pH regulation: characterization and functional investigation of H+ transporters in Stylophora pistillata

Background: Reef-building corals regularly experience changes in intra and extracellular H+ concentration ([H+]) due to physiological and environmental processes. Stringent control of [H+] is required for the maintenance of homeostatic acid-base balance in coral cells and is achieved through the regulation of intracellular pH (pHi). This task is especially challenging for reef-building corals that share an endosymbiotic relationship with photosynthetic dinoflagellates (family Symbiodinaceae), which exert a significant effect on the pHi of coral cells. Despite their importance, the pH regulatory proteins involved in the homeostatic acid-base balance have been scarcely investigated in corals. Here, we reported the full characterisation in terms of genomic structure, domain topology and phylogeny of three majors H+ transporter families implicated in pHi regulation; we investigated their tissue-specific expression and we assessed the effect of seawater acidification on their level of expression.

Results: We identified members of the Na+/Hexchanger (SLC9), vacuolar-type electrogenic H+-ATP hydrolases (V-ATPase) and voltage-gated proton channels (HvCN) families in the genome and transcriptome of S. pistillata. In addition, we identified a novel member of the HvCN gene family in the cnidarian subclass Hexacorallia, which has never been described in any species to date. We also reported key residues that participate to the H+ transporters substrate specificity, protein function and regulation. Lastly, we demonstrated that some of these have different tissue expression patterns and are mostly unaffected by exposure to seawater acidification.

Conclusions: In this study, we provide the first characterization of the Htransporters genes that contribute to homeostatic acid-base balance in coral cells. This work will enrich knowledge about basic aspects of coral biology, bearing important implications for our understanding of how corals regulate their intracellular environment.

Continue reading ‘Intracellular pH regulation: characterization and functional investigation of H+ transporters in Stylophora pistillata’

Acidification decreases microbial community diversity in the Salish Sea, a region with naturally high pCO2

Most literature exploring the biological effects of ocean acidification (OA) has focused on macroscopic organisms and far less is known about how marine microbial communities will respond. Studies of OA and microbial community composition and diversity have examined communities from a limited number of ocean regions where the ambient pH is near or above the global average. At San Juan Island (Salish Sea), a region that experiences naturally low pH (average = 7.8), the picoplankton (cell diameter is 0.2–2μm) community was predicted to show no response to experimental acidification in a three-week mesocosm experiment. Filtered seawater mesocosms were maintained via semicontinuous culturing. Three control mesocosms were maintained at pH 8.05 and three acidified mesocosms were maintained at pH 7.60. Total bacteria was quantified daily with a flow cytometer. Microbial communities were sampled every two days via filtration followed by DNA extraction, 16S rRNA amplification, and MiSeq sequencing. There was no significant difference in total bacteria between pH treatments throughout the experiment. Acidification significantly reduced Shannon’s diversity over time. During the final week of the experiment, acidification resulted in a significant decrease in Shannon’s diversity, Faith’s phylogenetic distance, and Pielous’s Evenness. ANCOM results revealed four bacterial ASVs (amplicon sequence variants), in families Flavobaceriaceae and Hyphomonadaceae that significantly decreased in relative frequency under acidification and two bacterial ASVs, in families Flavobacteriaceae and Alteromonadaceae, that significantly increased under acidification. This is the first OA study on the microbial community of the Salish Sea, a nutrient rich, low pH region, and the first of its kind to report a decrease in both picoplankton richness and evenness with acidification. These findings demonstrate that marine microbial communities that naturally experience acidic conditions are still sensitive to acidification.

Continue reading ‘Acidification decreases microbial community diversity in the Salish Sea, a region with naturally high pCO2’

Impact of ocean warming and acidification on symbiosis establishment and gene expression profiles in recruits of reef coral Acropora intermedia

The onset of symbiosis and the early development of most broadcast spawning corals play pivotal roles in recruitment success, yet these critical early stages are threatened by multiple stressors. However, molecular mechanisms governing these critical processes under ocean warming and acidification are still poorly understood. The present study investigated the interactive impact of elevated temperature (∼28.0°C and ∼30.5°C) and partial pressure of carbon dioxide (pCO2) (∼600 and ∼1,200 μatm) on early development and the gene expression patterns in juvenile Acropora intermedia over 33 days. The results showed that coral survival was >89% and was unaffected by high temperature, pCO2, or the combined treatment. Notably, high temperature completely arrested successful symbiosis establishment and the budding process, whereas acidification had a negligible effect. Moreover, there was a positive exponential relationship between symbiosis establishment and budding rates (y = 0.0004e6.43xR = 0.72, P < 0.0001), which indicated the importance of symbiosis in fueling asexual budding. Compared with corals at the control temperature (28°C), those under elevated temperature preferentially harbored Durusdinium spp., despite unsuccessful symbiosis establishment. In addition, compared to the control, 351 and 153 differentially expressed genes were detected in the symbiont and coral host in response to experimental conditions, respectively. In coral host, some genes involved in nutrient transportation and tissue fluorescence were affected by high temperature. In the symbionts, a suite of genes related to cell growth, ribosomal proteins, photosynthesis, and energy production was downregulated under high temperatures, which may have severely hampered successful cell proliferation of the endosymbionts and explains the failure of symbiosis establishment. Therefore, our results suggest that the responses of symbionts to future ocean conditions could play a vital role in shaping successful symbiosis in juvenile coral.

Continue reading ‘Impact of ocean warming and acidification on symbiosis establishment and gene expression profiles in recruits of reef coral Acropora intermedia’

Lack of oxidative damage on temperate juvenile catsharks after a long-term ocean acidification exposure

Ocean acidification is a consequence of chemical changes driven mainly by a continuous uptake of carbon dioxide, resulting in pH decrease. This phenomenon represents an additional threat to marine life, with expected effects ranging from changes in behavioral responses and calcification rates to the potential promotion of oxidative stress. To unravel the impacts of ocean acidification on the antioxidant system of sharks, we performed a long-term exposure (9 months, since early embryogenesis) to high CO2 conditions (pCO2 ~ 900 μatm) on a temperate shark (Scyliorhinus canicula). The following biomarkers were measured: enzymatic antioxidant defense (superoxide dismutase, catalase and glutathione peroxidase), protein repair and removal (heat shock proteins and ubiquitin), and oxidative damage on lipids (malondialdehyde) and DNA (8-hydroxy-2′-deoxyguanosine). Changes in the antioxidant enzyme defense were restricted to an increase in catalase activity in the muscle, an enzyme that plays a major role in oxidative stress mitigation. On the other hand, no evidence of oxidative damage was found, indicating that the observed increase in catalase activity may be enough to neutralize the effects of potentially higher reactive oxygen species. These results further indicate that these sharks’ antioxidant system can successfully cope with the levels of carbon dioxide projected for the end of the century. Nonetheless, the interaction between ocean acidification and the rise in temperature expected to occur in a near future may disturb their antioxidant capacity, requiring further investigation.

Continue reading ‘Lack of oxidative damage on temperate juvenile catsharks after a long-term ocean acidification exposure’

A new “business as usual” climate scenario and the stress response of the Caribbean coral Montastraea cavernosa

The climate change related decline of shallow (<30 m) coral reef ecosystems has been driven by the mortality of scleractinian corals caused primarily by the phenomenon known as “coral bleaching.” But despite pervasive phase shifts and macroalgal dominance on many coral reefs, some coral species have persisted. One of those species is Montastraea cavernosa which has been categorized as resilient to a range of biotic and abiotic stressors. In order to understand the mechanism(s) of resistance in this coral, we present the results of a thermal stress and ocean acidification (OA) experiment on M. cavernosa, both its brown and orange color morphs, representing conditions predicted by the Representative Concentration Pathway (RCP) 6.0 scenario in the year 2100. We assessed the community response of the prokaryotic microbiome, the photophysiological response of the endosymbiotic Symbiodiniaceae and the molecular responses of critical pathways in the host by quantifying transcript abundances of genes encoding fluorescent proteins, heat shock proteins, antioxidant enzymes and regulators of apoptosis. After a 12 d acclimatization experiment, no visible bleaching was observed in any treatment, and the excitation pressure on photosystem II of the symbiotic Symbiodiniaceae showed no effects of the independent or interactive effects of thermal stress and OA, while only minor, but significant, changes in the prokaryotic microbiome were observed when exposed to RCP 6.0 predicted OA conditions. At the end of the experiment, the host heat shock protein 90 showed an increase in transcript abundance under the combined effects of thermal stress and OA compared to high temperatures alone, but these treatment groups were not significantly different from treatments under normal temperatures. While Bax, an activator of apoptosis, was significantly higher under thermal stress alone compared to control samples. Taken together, M. cavernosa, exhibits ecological stability over time and this may be based on its physiological persistence, resistance and resilience when experimentally exposed to the ecologically realistic RCP 6.0 climate model predictions.

Continue reading ‘A new “business as usual” climate scenario and the stress response of the Caribbean coral Montastraea cavernosa’

Ocean acidification impedes gustation-mediated feeding behavior by disrupting gustatory signal transduction in the black sea bream, Acanthopagrus schlegelii

Highlights

  • Gustation-mediated feeding behavior of sea bream was significantly affected by OA.

  • Neurotransmitter levels and the expression of key genes were suppressed by OA.

  • OA hinders feeding of sea bream by obstructing gustatory signal transduction.

Abstract

Growing evidence suggests that ocean acidification (OA) may affect animal behaviors such as feeding. Although gustation plays a crucial role in evaluating the quality and palatability of food and ultimately influences whether or not teleosts consume the food, the potential impact of OA on gustation-mediated feeding behavior remains unknown. In this study, gustation mediated-feeding behavior, as indicated by the consumption rate (CR) and swallowing rate (SR) of agar pellets with or without feed upon OA exposure was investigated in black sea bream (Acanthopagrus schlegelii). Results showed that the exposure to acidified seawater led to significant reductions in the CR and SR of feed-containing agar pellets. In addition, the in vivo contents of three neurotransmitters and expression of genes from the gustatory signal transduction pathway were all significantly suppressed by the OA treatment. In general, the data obtained indicated that OA may hinder the gustation-mediated feeding behavior of A. schlegelii by disrupting gustatory signal transduction, which may aggravate the issue of food shortage for wild populations of black sea bream.

Continue reading ‘Ocean acidification impedes gustation-mediated feeding behavior by disrupting gustatory signal transduction in the black sea bream, Acanthopagrus schlegelii’


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